U.S. patent application number 14/638631 was filed with the patent office on 2016-09-08 for hybrid membrane and adsorption-based system and process for recovering co2 from flue gas and using combustion air for adsorbent regeneration.
This patent application is currently assigned to L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des Procedes Georges Claude. The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des Procedes Georges Claude. Invention is credited to Sudhir S. Kulkarni.
Application Number | 20160256819 14/638631 |
Document ID | / |
Family ID | 56850319 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160256819 |
Kind Code |
A1 |
Kulkarni; Sudhir S. |
September 8, 2016 |
HYBRID MEMBRANE AND ADSORPTION-BASED SYSTEM AND PROCESS FOR
RECOVERING CO2 FROM FLUE GAS AND USING COMBUSTION AIR FOR ADSORBENT
REGENERATION
Abstract
CO.sub.2 may be recovered from flue gas by a hybrid system
utilizing both gas separation membranes and adsorption. Purified
flue gas is separated by the gas separation membrane into permeate
and non-permeate streams. The permeate stream is compressed,
partially condensed at a heat exchanger, and phase-separated to
produce a vent gas and high purity liquid CO.sub.2. The vent gas is
recycled to the membrane. The non-permeate is fed to a PSA unit.
The CO.sub.2 blow-down from the PSA unit is also compressed with
the permeate stream. The adsorbent in the PSA unit is regenerated
with combustion air and the CO.sub.2-containing combustion air is
fed to a combustor for combustion with fuel and an oxidant to
produce the flue gas.
Inventors: |
Kulkarni; Sudhir S.;
(Wilmington, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour I'Etude et I'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Assignee: |
L'Air Liquide, Societe Anonyme pour
I'Etude et I'Exploitation des Procedes Georges Claude
Paris
FR
|
Family ID: |
56850319 |
Appl. No.: |
14/638631 |
Filed: |
March 4, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 53/047 20130101;
Y02E 20/326 20130101; Y02C 20/40 20200801; Y02P 20/152 20151101;
F23J 2219/70 20130101; B01D 2257/504 20130101; F23J 2215/50
20130101; B01D 53/002 20130101; Y02C 10/08 20130101; Y02P 20/151
20151101; C01B 32/50 20170801; F23J 2900/15061 20130101; F23J 15/02
20130101; B01D 2258/0283 20130101; Y02C 10/10 20130101; Y02E 20/32
20130101; B01D 53/229 20130101 |
International
Class: |
B01D 53/22 20060101
B01D053/22; C01B 31/20 20060101 C01B031/20; F23J 15/02 20060101
F23J015/02; B01D 53/047 20060101 B01D053/047; B01D 53/00 20060101
B01D053/00 |
Claims
1. A method for recovering CO.sub.2 from flue gas, comprising the
steps of: removing impurities from a flue gas stream to provide a
purified flue gas stream; compressing the purified flue gas stream
at a first compressor and feeding it to a gas separation membrane
unit comprising one or more gas separation membranes to produce a
permeate stream and a non-permeate stream deficient in CO.sub.2
compared to the permeate stream; compressing the permeate stream at
a second compressor; cooling the permeate stream to produce a
partially condensed permeate stream; separating the partially
condensed permeate stream into a CO.sub.2-deficient vent gas stream
deficient in CO.sub.2 compared to partially condensed permeate
stream and high purity liquid CO.sub.2 product; feeding the
CO.sub.2-deficient vent gas stream to the gas separation membrane
unit; feeding the non-permeate stream to a PSA unit comprising one
or more adsorbent beds to produce a further CO.sub.2-depleted vent
gas stream depleted in CO.sub.2 compared to the non-permeate
stream, a CO.sub.2 blow-down stream enriched in CO.sub.2 compared
to the non-permeate stream, and a regeneration product stream, the
regeneration product stream being produced by feeding a stream of
air to the PSA unit to regenerate one of said one or more adsorbent
beds and desorb CO.sub.2 therefrom, the regeneration product stream
being air enriched with the desorbed CO.sub.2; compressing the
CO.sub.2 blow-down stream at the second compressor to combine it
with the permeate stream; and combusting the regeneration product
stream at a combustor that produces the flue gas.
2. The method of claim 1, further comprising the step of cooling
the compressed purified flue gas stream at a heat exchanger to a
temperature ranging from 5.degree. C. to -60.degree. C.
3. The method of claim 2, further comprising the step of expanding
the further CO.sub.2-depleted vent gas stream to lower a
temperature thereof, wherein the compressed purified flue gas
stream is cooled through heat exchange at the heat exchanger with
the expanded further CO.sub.2-depleted vent gas stream.
4. The method of claim 2, wherein the compressed purified flue gas
stream is cooled through heat exchange at the heat exchanger with
the CO.sub.2-deficient vent gas stream prior to feeding the
CO.sub.2-deficient gas stream to the gas separation membrane
unit.
5. The method of claim 4, wherein the CO.sub.2-deficient vent gas
stream is heat exchanged two times with the compressed purified
flue gas stream and the CO.sub.2-deficient vent gas stream is
expanded to lower a temperature thereof in between the two
times.
6. The method of claim 2, further comprising the step of vaporizing
the high purity liquid CO.sub.2 product at the heat exchanger to
produce a high purity CO.sub.2 product gas, wherein the compressed
purified flue gas stream is cooled through heat exchange at the
heat exchanger with the high purity liquid CO.sub.2 product.
7. The method of claim 2, further comprising the step of expanding
the non-permeate stream to lower a temperature thereof prior to
being fed to the PSA unit, wherein compressed purified flue gas
stream is cooled through heat exchange at the heat exchanger with
the expanded non-permeate stream.
8. The method of claim 7, wherein the non-permeate stream is heat
exchanged two times with the compressed purified flue gas stream
and the non-permeate stream is expanded in between the two
times.
9. The method of claim 1, wherein said step of separating is
performed by separating the partially condensed permeate stream in
a phase separator.
10. The method of claim 1, wherein said step of separating is
performed by: separating the partially condensed permeate stream in
a first phase separator into a first CO.sub.2-deficient vent gas
stream deficient in CO.sub.2 compared to partially condensed
permeate stream and a first high purity liquid CO.sub.2 stream;
expanding the first CO.sub.2-deficient vent gas stream for partial
condensation thereof; separating the partially condensed first
CO.sub.2-deficient vent gas stream into a second CO.sub.2-deficient
vent gas stream deficient in CO.sub.2 compared to partially
condensed permeate stream and a second high purity liquid CO.sub.2
stream; and combining the first and second high purity liquid
CO.sub.2 streams to produce the high purity liquid CO.sub.2
product.
11. The method of claim 1, wherein said step of separating is
performed by: separating the partially condensed permeate stream in
a first phase separator into a first CO.sub.2-deficient vent gas
stream deficient in CO.sub.2 compared to partially condensed
permeate stream and a first high purity liquid CO.sub.2 stream;
expanding the first CO.sub.2-deficient vent gas stream for partial
condensation thereof; separating the partially condensed first
CO.sub.2-deficient vent gas stream into a second CO.sub.2-deficient
vent gas stream deficient in CO.sub.2 compared to partially
condensed permeate stream and a second high purity liquid CO.sub.2
stream; expanding each of the first and second high purity liquid
CO.sub.2 streams at first and second Joule-Thomson expanders;
feeding the expanded high purity liquid CO.sub.2 streams to a
distillation column; withdrawing the high purity liquid CO.sub.2
product from a bottom of the distillation column; and withdrawing a
CO.sub.2-deficient vapor stream from a top of the distillation
column, wherein the CO.sub.2-deficient vent gas stream is comprised
of the second CO.sub.2-deficient vent gas stream and the
CO.sub.2-deficient vapor stream.
12. A system for recovering CO.sub.2 from flue gas, comprising: a
combustor adapted and configured to combust fuel, oxidant, and
supplemental oxidant to produce a flue gas stream; a purification
unit in fluid communication with the combustor that is adapted and
configured to purify the flue gas stream and produce a purified
flue gas stream; a first compressor in fluid communication with the
purification unit that is adapted and configured to compress the
purified flue gas stream; a gas separation membrane unit in fluid
communication with the first compressor that comprising one or more
gas separation membranes adapted and configured to receive a feed
gas stream from the first compressor and separate the feed gas
stream into a permeate gas stream and a non-permeate gas stream
that is deficient in CO.sub.2 compared to the permeate gas stream;
a second compressor in fluid communication with the gas separation
membrane unit that is adapted and configured to receive and
compress the permeate gas stream to produce a compressed permeate
gas stream; at least one heat exchanger, at least one of the at
least one heat exchanger being in heat transfer relation with the
compressed permeate gas stream and being adapted and configured to
cool the compressed permeate gas stream to produce a partially
condensed permeate stream, at least one of the at least one heat
exchanger being in heat transfer relation with the feed gas stream;
a PSA unit comprising one or more adsorbent beds in fluid
communication with the gas separation membrane unit that is adapted
and configured to receive the non-permeate gas stream and an air
stream and produce a CO.sub.2 blow-down gas stream enriched in
CO.sub.2 compared to the non-permeate gas stream, a further
CO.sub.2-depleted vent gas stream, and a regeneration product
stream, the one or more adsorbent beds being adapted and configured
to adsorb CO.sub.2 from the non-permeate stream, the regeneration
product stream comprising air and CO.sub.2 desorbed from the one or
more adsorbent beds by the air stream, the combustor being further
adapted and configured to receive the regeneration product stream
from the PSA unit, the second compressor being further adapted and
configured to compress the CO.sub.2 blow-down stream along with the
permeate stream; and a phase separation unit in fluid communication
with the second compressor that is adapted and configured to
receive the partially condensed permeate stream from the heat
exchanger and separate the partially condensed permeate stream into
a CO.sub.2-deficient vent gas stream deficient in CO.sub.2 compared
to partially condensed permeate stream and a high purity liquid
CO.sub.2 stream, wherein the feed gas is a combination of the
compressed purified flue gas and the CO.sub.2-deficient vent gas
stream.
13. The system of claim 12, further comprising an expander adapted
and configured to expand the further CO.sub.2-depleted vent gas
stream to lower a temperature of the further CO.sub.2-depleted vent
gas stream, wherein at least one of the at least one heat exchanger
is in heat transfer relation between, on one hand, the further
CO.sub.2-depleted vent gas stream, and on the other hand, either
the feed gas stream or the compressed permeate stream.
14. The system of claim 12, wherein at least one of the at least
one heat exchanger is in heat transfer relation between the feed
gas stream and the CO.sub.2-deficient vent gas stream.
15. The system of claim 12, wherein at least one of the at least
one heat exchanger is in heat transfer relation between the high
purity liquid CO.sub.2 product and the feed gas stream and is
further adapted and configured to vaporize the high purity liquid
CO.sub.2 product to produce a high purity CO.sub.2 gas product.
16. The system of claim 12, further comprising an expander that is
adapted and configured to expand the non-permeate stream to lower a
temperature thereof, wherein at least one of the at least one heat
exchanger is in heat transfer relation between the expanded
non-permeate stream and the feed gas stream.
17. The system of claim 12, wherein the phase separation unit
comprises one phase separator vessel.
18. The system of claim 12, wherein: the phase separation unit
comprises first and second phase separator vessels and a
Joule-Thomson expander; the first phase separator vessel is in
fluid communication with the second compressor and is adapted and
configured to receive the partially condensed permeate stream for
phase separation into a first CO.sub.2-deficient vent gas stream
and a first liquid CO.sub.2 stream; the Joule-Thomson expander is
in fluid communication between the first and second phase separator
vessels and is adapted and configured to expand the first
CO.sub.2-deficient vent gas stream for partial condensation
thereof; the second phase separator vessel is in fluid
communication with the Joule-Thomson valve and is adapted and
configured to receive the partially condensed first
CO.sub.2-deficient vent gas stream for separation into a second
CO.sub.2-deficient vent gas stream and a second liquid CO.sub.2
stream; the high purity liquid CO.sub.2 product is comprised of the
first and second high purity liquid CO.sub.2 streams; and the first
compressor is in fluid communication with the second phase
separator vessel to receive the second CO.sub.2-deficient vent gas
stream as the CO.sub.2-deficient vent gas stream.
19. The system of claim 12, wherein: the phase separation unit
comprising first and second phase separator vessels, first, second,
and third Joule-Thomson valves, and a distillation column; the
first phase separator vessel is in fluid communication with the
second compressor and is adapted and configured to receive the
partially condensed permeate stream for phase separation into a
first CO.sub.2-deficient vent gas stream and a first liquid
CO.sub.2 stream; the first Joule-Thomson expander is in fluid
communication between the first and second phase separator vessels
and is adapted and configured to expand the first
CO.sub.2-deficient vent gas stream for partial condensation
thereof; the second phase separator vessel is in fluid
communication with the first Joule-Thomson valve and is adapted and
configured to receive the partially condensed first
CO.sub.2-deficient vent gas stream for separation into a second
CO.sub.2-deficient vent gas stream and a second liquid CO.sub.2
stream; the second and third Joule-Thomson valves are in fluid
communication between the first and second phase separator vessel,
respectively, and the distillation column; the second and third
Joule-Thomas valves are adapted and configured to expand the first
and second liquid CO.sub.2 streams; the distillation column is
adapted and configured to receive the expanded first and second
liquid CO.sub.2 streams and produce a high purity liquid CO.sub.2
stream and a CO.sub.2-deficient vapor stream; the high purity
liquid CO.sub.2 product is comprised of the high purity liquid
CO.sub.2 stream; and first compressor is in fluid communication
with the second phase separator vessel to receive the second
CO.sub.2-deficient vent gas stream and the distillation column to
receive the CO.sub.2-deficient vapor stream.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] None.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a process and apparatus for
the separation of gaseous mixture containing carbon dioxide as main
component. It relates in particular to processes and apparatus for
purifying carbon dioxide, for example coming from combustion of a
carbon containing fuel, such as takes place in an air-fired or
oxycombustion fossil fuel or biomass power plant.
[0004] 2. Related Art
[0005] Various techniques based on solvent, sorbents, and membranes
have been proposed for CO.sub.2 capture from power plants or
industrial sources. Some techniques utilize a medium (e.g., amines)
for capturing CO.sub.2 through chemical affinity. However, the
energy needed for regenerating the medium (having chemical affinity
for CO.sub.2) is significantly high. Other solvents and adsorbents
capture CO.sub.2 through physical affinity. While the energy
necessary for regenerating such solvents and adsorbents is
relatively lower than that the media having chemical affinity for
CO.sub.2, they typically have a relatively lower capacity for
CO.sub.2 resulting in higher equipment capital costs On the other
hand, membranes use a combination of physical affinity and
diffusivity. The driving force for transport through membranes is
the difference between CO.sub.2 partial pressure across the
membrane (i.e., the feed partial pressure minus the permeate
partial pressure).
[0006] Regardless of the technique employed to recover CO.sub.2,
high CO.sub.2 recoveries from feed gases is desirable for a variety
of reasons. For example, the U.S. Department of Energy (DOE) has
set a target recovery for recovering CO.sub.2 from power plants. As
another example, high CO.sub.2 recoveries allow more CO.sub.2
product gas to be sold or used in order to recover the costs
associated with the pre-treatment of the flue gas necessary for
recovery. However, in the case of CO.sub.2 recovery utilizing
membrane separation, as more and more CO.sub.2 is sought to be
recovered, the driving force across the membrane decreases and
approaches a pinch point beyond which additional recovery comes at
the expense of high compression energy costs or high membrane
surface areas. Thus, for some levels of CO.sub.2 recovery, this
problem has the potential to increase capital and operating
expenses to unsatisfactory levels.
[0007] Each of U.S. Pat. No. 8,617,292, U.S. Pat. No. 8,663,364,
and U.S. Pat. No. 8,734,569 discloses that operation of membranes
at relatively cold temperatures is highly effective for CO.sub.2
capture. Cold temperature operation leads to high membrane
selectivity with negligible membrane permeance loss or even
possibly an enhancement in membrane permeance. While operation of
cold membranes is quite efficient, higher and higher CO.sub.2
recoveries may be desired without concomitant unsatisfactorily high
increases in capital and operating expenses.
[0008] Membranes are known to be efficient for bulk separation of
gases when the driving force is high. They have been used in
combination with other, subsequent, gas separation techniques in
order to achieve an overall CO.sub.2 recovery. Such hybrid systems
are known where a membrane performs a bulk CO.sub.2 separation from
natural gas followed by amine treatment of the lower concentration
membrane residue stream. Hybrid combinations of solvent (e.g.
piperazine) and membrane have also been studied for CO.sub.2
capture from flue gas.
[0009] One particular two unit separation process is disclosed by
U.S. Pat. No. 8,728,201 including a membrane utilizing a vacuum on
a permeate side that is followed with an absorption (solvent) to
remove CO.sub.2 from the membrane residue. There is little
integration between the two unit operations.
[0010] One particular U.S. Department of Energy funded project uses
a costly and cumbersome plate and frame membrane system to operate
with an air sweep at low pressures. In this approach, the membrane
is placed in series--after the solvent unit or in parallel with the
solvent unit (Freeman, et al. "Bench-Scale Development of a Hybrid
Membrane-Absorption CO.sub.2 Capture Process (DE-FE0013118)", Dec.
20, 2013 Kickoff Meeting).
[0011] Hybrid processes combining adsorption and membranes are also
known. For example, U.S. Pat. No. 8,591,769 and U.S. Pat. No.
6,183,628 discuss membrane treatment of PSA vent gas to recover
H.sub.2. However, if this technique was applied to flue gas, such a
scheme would require use of a less optimum adsorbent that is
exposed to many impurities Co-adsorption of moisture and other acid
gas components in flue gas prevents optimum adsorption of
CO.sub.2.
[0012] WO14009449 A1 proposes to combine membrane and adsorption
processes for moisture removal.
[0013] Membranes can be swept with a sweep gas in order to overcome
the above-described membrane driving force pinch problem. U.S. Pat.
No. 8,734,569 discloses that this can be done by diverting a small
fraction of gas (that is derived from the low CO.sub.2
concentration residue) to sweep the permeate side of a membrane
module. For a low sweep rate, the permeate CO.sub.2 concentration
decreases marginally but the membrane area can be decreased
significantly. However for high sweep rates, permeate CO.sub.2
concentrations can decrease significantly.
[0014] Another sweep concept, particularly applicable to CO.sub.2
capture from flue gas, utilizes a two step membrane process
(Merkel, et al., "Power plant post-combustion carbon dioxide
capture: An opportunity for membranes", Journal of Membrane Science
359 (2010) 126-139). The 1.sup.st permeate at relatively high
CO.sub.2 purity is sent for further CO.sub.2 purification. The
2.sup.nd membrane is swept with an air stream to achieve high
CO.sub.2 recovery. The air stream is then sent to the boiler island
where the recovered CO.sub.2 dilutes the overall stream, imposing a
small energy penalty for combustion.
SUMMARY OF THE INVENTION
[0015] There is a need for membrane-based CO.sub.2 recovery
processes that do not require unsatisfactorily high capital and
operating expenses.
[0016] There is also a need for increased integration of hybrid
membrane gas separation schemes for recovery of CO.sub.2,
especially from flue gas.
[0017] There is a yet another need for a hybrid membrane gas
separation scheme for recovery of CO.sub.2, especially from flue
gas, that does not require the use of less than optimal adsorbents
and/or adsorbents which must be contacted with too many
impurities.
[0018] There is yet another need for a sweep gas-based membrane
separation scheme for recovery of CO.sub.2, especially from flue
gas, that that does not result in an unsatisfactory decrease in the
permeate CO.sub.2 concentration.
[0019] There is disclosed a method for recovering CO.sub.2 from
flue gas that comprises the following steps. Impurities are removed
from a flue gas stream to provide a purified flue gas stream. The
purified flue gas stream is compressed at a first compressor and
fed to a gas separation membrane unit comprising one or more gas
separation membranes to produce a permeate stream and a
non-permeate stream deficient in CO.sub.2 compared to the permeate
stream. The permeate stream is compressed at a second compressor.
The permeate stream is cooled to produce a partially condensed
permeate stream. The partially condensed permeate stream is
separated into a CO.sub.2-deficient vent gas stream deficient in
CO.sub.2 compared to partially condensed permeate stream and high
purity liquid CO.sub.2 product. The CO.sub.2-deficient vent gas
stream is recycled to the gas separation membrane unit. The
non-permeate stream is fed to a PSA unit comprising one or more
adsorbent beds to produce a further CO.sub.2-depleted vent gas
stream depleted in CO.sub.2 compared to the non-permeate stream, a
CO.sub.2 blow-down stream enriched in CO.sub.2 compared to the
non-permeate stream, and a regeneration product stream. The
CO.sub.2 blow-down stream is compressed at the second compressor
along with the permeate stream. The regeneration product stream is
combusted at a combustor that produces the flue gas. The
regeneration product stream is produced by feeding a stream of air
to the PSA unit to regenerate one of said one or more adsorbent
beds and desorb CO.sub.2 therefrom. The regeneration product stream
is air enriched with the desorbed CO.sub.2.
[0020] There is disclosed a system for recovering CO.sub.2 from
flue gas, comprising: a combustor adapted and configured to combust
fuel, oxidant, and supplemental oxidant to produce a flue gas
stream; a purification unit in fluid communication with the
combustor that is adapted and configured to purify the flue gas
stream and produce a purified flue gas stream; a first compressor
in fluid communication with the purification unit that is adapted
and configured to compress the purified flue gas stream; a gas
separation membrane unit in fluid communication with the first
compressor that comprising one or more gas separation membranes
adapted and configured to receive a feed gas stream from the first
compressor and separate the feed gas stream into a permeate gas
stream and a non-permeate gas stream that is deficient in CO.sub.2
compared to the permeate gas stream; a second compressor in fluid
communication with the gas separation membrane unit that is adapted
and configured to receive and compress the permeate gas stream to
produce a compressed permeate gas stream; at least one heat
exchanger, at least one of the at least one heat exchanger being in
heat transfer relation with the compressed permeate gas stream and
being adapted and configured to partially condense the compressed
permeate gas stream to produce a partially condensed permeate
stream, at least one of the at least one heat exchanger being in
heat transfer relation with the feed gas stream; a PSA unit
comprising one or more adsorbent beds in fluid communication with
the gas separation membrane unit that is adapted and configured to
receive the non-permeate gas stream and an air stream and produce a
CO.sub.2 blow-down gas stream is enriched in CO.sub.2 compared to
the non-permeate gas stream, a further CO.sub.2-depleted vent gas
stream, and a regeneration product stream, the one or more
adsorbent beds being adapted and configured to adsorb CO.sub.2 from
the non-permeate stream, the regeneration product stream comprising
air and CO.sub.2 desorbed from the one or more adsorbent beds by
the air stream, the second compressor being further adapted and
configured to compress the CO.sub.2 blow-down stream from the PSA
unit along with the permeate stream, the combustor being further
adapted and configured to receive the regeneration product stream
from the PSA unit; and a phase separation unit in fluid
communication with the second compressor that is adapted and
configured to receive the partially condensed permeate stream from
the heat exchanger and separate the partially condensed permeate
stream into a CO.sub.2-deficient vent gas stream deficient in
CO.sub.2 compared to partially condensed permeate stream and a high
purity liquid CO.sub.2 stream, wherein the first compressor is
further adapted and configured to compress the CO.sub.2-deficient
vent gas stream along with the compressed purified flue gas.
[0021] The method and/or system may include one or more of the
following aspects:
[0022] the compressed purified flue gas stream is cooled at a heat
exchanger to a temperature ranging from 20.degree. C. to
-60.degree. C.
[0023] the further CO.sub.2-depleted vent gas stream is expanded to
lower a temperature thereof, wherein the compressed purified flue
gas stream is cooled through heat exchange at the heat exchanger
with the expanded further CO.sub.2-depleted vent gas stream.
[0024] the compressed purified flue gas stream is cooled through
heat exchange at the heat exchanger with the CO.sub.2-deficient
vent gas stream prior to feeding the CO.sub.2-deficient gas stream
to the gas separation membrane unit.
[0025] the CO.sub.2-deficient vent gas stream is heat exchanged two
times with the compressed purified flue gas stream and the
CO.sub.2-deficient vent gas stream is expanded to lower a
temperature thereof in between the two times.
[0026] the high purity liquid CO.sub.2 product is vaporized at the
heat exchanger to produce a high purity CO.sub.2 product gas,
wherein the compressed purified flue gas stream is cooled through
heat exchange at the heat exchanger with the high purity liquid
CO.sub.2 product.
[0027] the non-permeate stream is expanded to lower a temperature
thereof prior to being fed to the PSA unit, wherein compressed
purified flue gas stream is cooled through heat exchange at the
heat exchanger with the expanded non-permeate stream.
[0028] the non-permeate stream is heat exchanged two times with the
compressed purified flue gas stream and the non-permeate stream is
expanded in between the two times.
[0029] said step of separating is performed by separating the
partially condensed permeate stream in a phase separator.
[0030] step of separating is performed by: separating the partially
condensed permeate stream in a first phase separator into a first
CO.sub.2-deficient vent gas stream deficient in CO.sub.2 compared
to partially condensed permeate stream and a first high purity
liquid CO.sub.2 stream; expanding the first CO.sub.2-deficient vent
gas stream for partial condensation thereof; separating the
partially condensed first CO.sub.2-deficient vent gas stream into a
second CO.sub.2-deficient vent gas stream deficient in CO.sub.2
compared to partially condensed permeate stream and a second high
purity liquid CO.sub.2 stream; and combining the first and second
high purity liquid CO.sub.2 streams to produce the high purity
liquid CO.sub.2 product.
[0031] said step of separating is performed by: separating the
partially condensed permeate stream in a first phase separator into
a first CO.sub.2-deficient vent gas stream deficient in CO.sub.2
compared to partially condensed permeate stream and a first high
purity liquid CO.sub.2 stream; expanding the first
CO.sub.2-deficient vent gas stream for partial condensation
thereof; separating the partially condensed first
CO.sub.2-deficient vent gas stream into a second CO.sub.2-deficient
vent gas stream deficient in CO.sub.2 compared to partially
condensed permeate stream and a second high purity liquid CO.sub.2
stream; expanding each of the first and second high purity liquid
CO.sub.2 streams at first and second Joule-Thomson expanders;
feeding the expanded high purity liquid CO.sub.2 streams to a
distillation column; withdrawing the high purity liquid CO.sub.2
product from a bottom of the distillation column; and withdrawing a
CO.sub.2-deficient vapor stream from a top of the distillation
column, wherein the CO.sub.2-deficient vent gas stream is comprised
of the second CO.sub.2-deficient vent gas stream and the
CO.sub.2-deficient vapor stream.
[0032] an expander is adapted and configured to expand the further
CO.sub.2-depleted vent gas stream to lower a temperature of the
further CO.sub.2-depleted vent gas stream, wherein at least one of
the at least one heat exchanger is in heat transfer relation
between, on one hand, the further CO.sub.2-depleted vent gas
stream, and on the other hand, either the feed gas stream or the
compressed permeate stream.
[0033] at least one of the at least one heat exchanger is in heat
transfer relation between the feed gas stream and the
CO.sub.2-deficient vent gas stream.
[0034] at least one of the at least one heat exchanger is in heat
transfer relation between the high purity liquid CO.sub.2 product
and the feed gas stream and is further adapted and configured to
vaporize the high purity liquid CO.sub.2 product to produce a high
purity CO.sub.2 gas product.
[0035] an expander is adapted and configured to expand the
non-permeate stream to lower a temperature thereof, wherein at
least one of the at least one heat exchanger is in heat transfer
relation between the expanded non-permeate stream and the feed gas
stream.
[0036] the phase separation unit comprises one phase separator
vessel.
[0037] the phase separation unit comprises first and second phase
separator vessels and a Joule-Thomson expander; the first phase
separator vessel is in fluid communication with the second
compressor and is adapted and configured to receive the partially
condensed permeate stream for phase separation into a first
CO.sub.2-deficient vent gas stream and a first liquid CO.sub.2
stream; the Joule-Thomson expander is in fluid communication
between the first and second phase separator vessels and is adapted
and configured to expand the first CO.sub.2-deficient vent gas
stream for partial condensation thereof; the second phase separator
vessel is in fluid communication with the Joule-Thomson valve and
is adapted and configured to receive the partially condensed first
CO.sub.2-deficient vent gas stream for separation into a second
CO.sub.2-deficient vent gas stream and a second liquid CO.sub.2
stream; the high purity liquid CO.sub.2 product is comprised of the
first and second high purity liquid CO.sub.2 streams; and the first
compressor is in fluid communication with the second phase
separator vessel to receive the second CO.sub.2-deficient vent gas
stream as the CO.sub.2-deficient vent gas stream.
[0038] the phase separation unit comprises first and second phase
separator vessels, first, second, and third Joule-Thomson valves,
and a distillation column; the first phase separator vessel is in
fluid communication with the second compressor and is adapted and
configured to receive the partially condensed permeate stream for
phase separation into a first CO.sub.2-deficient vent gas stream
and a first liquid CO.sub.2 stream; the first Joule-Thomson
expander is in fluid communication between the first and second
phase separator vessels and is adapted and configured to expand the
first CO.sub.2-deficient vent gas stream for partial condensation
thereof; the second phase separator vessel is in fluid
communication with the first Joule-Thomson valve and is adapted and
configured to receive the partially condensed first
CO.sub.2-deficient vent gas stream for separation into a second
CO.sub.2-deficient vent gas stream and a second liquid CO.sub.2
stream; the second and third Joule-Thomson valves are in fluid
communication between the first and second phase separator vessel,
respectively, and the distillation column; the second and third
Joule-Thomas valves are adapted and configured to expand the first
and second liquid CO.sub.2 streams; the distillation column is
adapted and configured to receive the expanded first and second
liquid CO.sub.2 streams and produce a high purity liquid CO.sub.2
stream and a CO.sub.2-deficient vapor stream; the high purity
liquid CO.sub.2 product is comprised of the high purity liquid
CO.sub.2 stream; and first compressor is in fluid communication
with the second phase separator vessel to receive the second
CO.sub.2-deficient vent gas stream and the distillation column to
receive the CO.sub.2-deficient vapor stream.
[0039] the flue gas contains 3-90% vol CO.sub.2.
[0040] a non-CO.sub.2 balance of the flue gas is predominantly
N.sub.2.
[0041] the flue gas is obtained from an air-fired coal combustion
plant and contains 8-16% vol CO.sub.2.
[0042] the flue gas is obtained from an air-fired natural gas
combustion plant and contains 3-10% vol CO.sub.2.
[0043] the flue gas is obtained from an oxycoal combustion plant
combusting coal with pure oxygen or synthetic air and contains
60-90% vol CO.sub.2.
[0044] the flue gas is obtained from a steam methane reformer and
contains 15-90% vol CO.sub.2.
[0045] the flue gas is obtained from a blast furnace and contains
20-90% CO.sub.2.
[0046] the flue gas comprises 4-30% vol CO.sub.2.
BRIEF DESCRIPTIONS OF THE DRAWINGS
[0047] FIG. 1 is a schematic of the inventive method and
system.
[0048] FIG. 2 is a schematic of an embodiment of the inventive
method and system.
[0049] FIG. 3 is a schematic of another embodiment of the inventive
method and system.
[0050] FIG. 4 is a schematic of a two-phase separator alternative
to the single phase separator of FIG. 2 or FIG. 3.
[0051] FIG. 5 is a schematic of a two-phase separator plus
distillation column alternative to the single phase separator of
FIG. 2 or FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0052] Disclosed is a method and system of recovering CO.sub.2 from
flue gas to provide purified CO.sub.2. The method combines the
benefits of the gas separation techniques of membranes and
adsorption, but integrates the two to maximize efficiencies. For
example, a recovery of greater than approximately 90% of the
CO.sub.2 from the flue gas of an existing air-fired coal power
plant may be possible with a less than approximately 35% increase
in the plant's cost of electricity.
[0053] The flue gas may be obtained or derived from suitable
combustion processes such as steam methane reforming (SMR), blast
furnaces, and air-fired or oxygen-enhanced combustion of fossil
fuels (such as in power plants). In the case of oxygen-enhanced
fossil fuel combustion processes, the combustion may be full
oxycombustion or partial oxycombustion. In full oxycombustion, the
primary and secondary oxidants (and tertiary and quaternary
oxidants, if present) may be pure oxygen or synthetic air
comprising oxygen and recycled flue gas. In partial oxycombustion,
one or more of the oxidants may be air and one or more of the
remaining oxidants may be oxygen or synthetic air (a mixture of
oxygen and recycled flue gas), or alternatively, one or more of the
oxidants may be oxygen-enriched air. Pure oxygen means that the
oxidant has a concentration typically found in conventional
industrial oxygen production processes such as in cryogenic air
separation units. The oxygen concentration of synthetic air may
range from a concentration at, or above that, of oxygen in air to a
concentration less than pure oxygen.
[0054] The flue gas contains 3-90% vol CO.sub.2. Other components
that may be contained within the flue gas include but are not
limited to other combustion byproducts, such as water, methane,
nitrogen, oxygen, argon, carbon monoxide, oxides of sulfur, and
oxides of nitrogen. Typically, the non-CO.sub.2 balance of the flue
gas is predominantly N.sub.2. Flue gas obtained from an air-fired
coal combustion plant typically contains 8-16% vol CO.sub.2, while
flue gas obtained from an air-fired natural gas combustion plant
typically contains 3-10% vol CO.sub.2. Flue gas obtained from an
oxycoal combustion plant (i.e., coal combusted with pure oxygen or
synthetic air) typically contains 60-90% vol CO.sub.2 with a
balance of water, nitrogen, oxygen, argon, carbon monoxide, oxides
of sulfur, and oxides of nitrogen. Flue gas obtained from a steam
methane reformer typically contains 15-90% vol CO.sub.2 with a
balance of water, methane, nitrogen, oxygen, argon, carbon
monoxide, oxides of sulfur, and oxides of nitrogen. Flue gas
obtained from a blast furnace typically contains 20-90% CO.sub.2
with a balance of water, hydrogen, nitrogen, oxygen, argon, carbon
monoxide, oxides of sulfur, and oxides of nitrogen. Typically, the
flue gas comprises 4-30% vol CO.sub.2.
[0055] As best illustrated in FIG. 1, a fuel stream 51, one or more
oxidant streams 52 and a supplemental oxidant stream 66 are
combusted at a combustor 1, thereby producing a raw flue gas stream
53. While the type of fuel in fuel stream 51 and the type of
combustor 1 are not limited, typically the fuel is natural gas or
coal and the combustor 1 is a boiler. One or more streams of the
one or more oxidant streams 52 may be air, oxygen-enriched air,
and/or industrially pure oxygen. The supplemental oxidant stream 66
is described below. It or they may be fed as primary air with or
without secondary air, tertiary air, and quaternary air. One of
ordinary skill in the field of combustion will recognize that the
terms "primary air", "secondary air", "tertiary air", and
"quaternary air" are not meant as being limited to air, but rather
encompass oxygen-enriched air and industrially pure oxygen as
well.
[0056] Raw stream 53 is fed to a purification unit 2 for removal of
impurities. Suitable treatment methods include but are not limited
to those disclosed in WO 2009010690, WO 2009095581, and U.S.
Published Patent Application Nos. US 2009013717, US2009013868, and
US2009013871, the treatment methods of which are incorporated
herein by reference in their entireties. The moisture content of
the raw stream 53 should be reduced to a low level for a variety of
reasons. First, it is desirable to avoid competition for the
adsorbent (in the downstream PSA unit 7) by moisture and CO.sub.2.
In the case of sub-ambient membrane operation in gas separation
membrane unit 4, it is desirable to avoid the freezing of moisture
on cold surfaces in any heat exchanger present. Known drying
materials and adsorbent-based processes include alumina, silica, or
molecular sieves. Condensation of moisture through cooling may also
be used to lower the moisture content of raw gas stream 53. In
addition to moisture, the purification unit 2 typically removes
particulates with filters and acid gases, such as NO.sub.x and
So.sub.x, with scrubbers.
[0057] The purified flue gas stream 54 is then compressed at a
compression unit 3 to boost its pressure to about 4-20 bar. The
compression unit 3 includes one or more compressors. In between
multiple compression stages (in the case of a multi-stage
compressor), stream 54 may be cooled with water, other non-water
coolant, or a coolant gas whereby additional water may be removed
from stream 54 through condensation (i.e., knocked out). In the
case of a boiler for combustor 1, stream 54 may be cooled with
boiler feed water. In this manner, the boiler feed water may be
pre-heated prior to introduction in the boiler combustor 1 and the
efficiency of the boiler combustor 1 and compression unit 3 are
both increased. For example, when stream 54 is compressed to 16
bar, sufficient heat is generated to pre-heat boiler feed water to
approximately 147.degree. C. In a coal power plant, such
pre-heating allows more steam turbine energy to be used for
electricity generation. Suitable types of compressors include
centrifugal, screw, reciprocating, and axial compressors.
[0058] With continued reference to FIG. 1, compressed, purified
flue gas stream 55 is fed to an inlet of a gas separation membrane
unit 4. The membranes of the gas separation membrane unit 4 allow
selective permeation to form a low pressure CO.sub.2 enriched
permeate stream 57 and a CO.sub.2 depleted stream non-permeate
stream 58. The gas separation membranes of unit 4 may be operated
at ambient or sub-ambient temperature.
[0059] When the gas separation membranes of unit 4 are operated at
ambient temperature, the upstream water cooling is sufficient to
bring stream 55 to ambient temperature.
[0060] When the membrane is operated at a sub-ambient temperature,
such as 5.degree. C. to -60.degree. C., the required cold
temperature is achieved through heat exchange between stream 56 and
non-permeate stream 58 (after expansion of stream 58) and/or
between stream 56 and PSA vent gas 64 (after expansion of stream
64). This heat exchange may be accomplished with a conventional
heat exchanger, such as a plate fin, shell-in-tube, spiral wound,
or brazed aluminum plate heat exchanger, or it may be a falling
film evaporator as disclosed in EP 1008826, a heat exchanger
derived from an automobile radiator as disclosed in US 2009/211733,
or plate heat exchangers manufactured as disclosed in FR 2,930,464,
FR 2,930,465, and FR 2,930,466. The heat exchangers in the cited
patent publications are all incorporated herein by reference in
their entireties. Typically, the heat exchanger is a brazed
aluminum plate exchanger having multiple parallel cores allowing it
to cool/heat a number of streams. The temperature of stream 54
should be maintained above its water freezing point. It should be
noted that, with regard to all heating or cooling steps performed
at heat exchangers, the skilled artisan will recognize that
selection of which stream or streams are used to cool another
stream or streams at a particular heat exchanger is well within the
knowledge of a chemical engineer in the field of industrial
gases.
[0061] The permeate stream 57 is fed to a suction inlet of a
compression unit 5 where the combined stream is compressed to about
16-30 bar. The compression unit 5 contains one or more compressors
selected from centrifugal, screw, reciprocating, and axial
compressors. The compression unit 5 also typically uses boiler feed
water for cooling of stream 57 so that further water may be knocked
out (or optionally, to avoid flooding of a water removal adsorbent)
and the boiler feed water may be preheated.
[0062] With continued reference to FIG. 1, the compressed stream
60, typically containing >60% vol CO.sub.2) is then fed to a
liquefaction unit 6 to produce high purity (<95% vol) liquid
CO.sub.2 and a vent gas stream 62. The high purity liquid CO.sub.2
is re-gasified to produce gaseous CO.sub.2 product 59. The cold
temperature required for liquefaction of the CO.sub.2 is
substantially generated through heat exchange with stream 58 (after
expansion) and/or stream 64 (after expansion). The cold temperature
required for liquefaction may optionally also be generated through
heat exchange with a portion of the high purity liquid CO.sub.2 so
as to cool compressed stream 60 and vaporize the high purity liquid
CO.sub.2. The liquefaction unit 6 may also include a pump to boost
the pressure of high purity liquid CO.sub.2 prior to
re-gasification to produce the CO.sub.2 product 61.
[0063] The CO.sub.2-depleted vent gas 62, containing about 20-40%
vol CO.sub.2, is also fed to the gas separation membrane unit 4.
Depending upon the pressure of the CO.sub.2-depleted vent gas 62,
it can first be expanded to the pressure of stream 55 as
necessary.
[0064] The non-permeate stream 58, containing about 4-15% vol
CO.sub.2, is fed to pressure swing adsorption (PSA) unit 7. The PSA
unit 7 contains a plurality of adsorbent columns. At PSA unit 7,
CO.sub.2 from stream 58 is selectively adsorbed so that a further
CO.sub.2 depleted vent gas 64 is produced that contains anywhere
from 10 ppm vol to 4% vol of CO.sub.2. The CO.sub.2 depleted vent
gas 64 is expanded at a turbo-expander 8 to recover useful energy
and vented to atmosphere as stream 65.
[0065] The adsorbed CO.sub.2 is partially recovered as a CO.sub.2
blow-down stream 69. The CO.sub.2 concentration of the CO.sub.2
blow-down stream 69 is equal to or higher than that of stream 58
and is fed to the suction inlet of compressor 5. In the event that
the CO.sub.2 concentration for the CO.sub.2 blow-down stream 69 is
lower than that of stream 58, as shown by the dotted line, it may
instead be fed to the suction inlet of compressor 3.
[0066] With continued reference to FIG. 1, the adsorbent in PSA
unit 7 is regenerated by an air stream 63, thereby producing a vent
stream 66 that contains air and substantially the remaining
desorbed CO.sub.2. The air and desorbed CO.sub.2-containing stream
66 is fed to combustor 1 as the entirety of, or as a portion of,
the primary, secondary, tertiary (if present), and/or quaternary
(if present) oxidant that is fed to the combustor. Stream 66 may be
mixed with a portion of oxidant from one or more of streams 52 or
may be fed to combustor 1 separately from streams 52. A wide
variety of oxidant injection schemes are known in the field of
combustion (especially combustion performed with recycled flue gas)
and their details need not be recited herein. Some degree of
moisture may remain adsorbed on adsorbent in PSA unit 7 after
CO.sub.2 desorption. In order to more effectively desorb that
moisture, a portion of the air of stream 63 may either be dried
(e.g. with zeolite 3A) or pre-heated upstream of PSA unit 7.
[0067] As shown in FIG. 2, one embodiment includes sub-ambient
membrane separation and expansion of a non-permeate stream
downstream of PSA separation.
[0068] Fuel 51 with one or more oxidant streams 52 and supplemental
oxidant stream 66 are combusted in combustor 1 which is a boiler.
The resulting flue gas stream 53 is purified in purification unit 2
for removal of impurities as described above. The purification unit
2 may optionally include a blower in order to provide adequate
suction pressure for compressor 3.
[0069] As described above, the purified flue gas stream 54 is fed
to the suction inlet of a compressor 3. As described above,
compressor 3 may include one or more compressors which also
typically includes water cooling of the compressed CO.sub.2
enriched stream that may be used to preheat boiler feed water and
for further water knock-out.
[0070] The compressed, purified flue gas stream 55 after water
cooling is dried with an adsorbent-based moisture removal unit 9
that contains one or more adsorbent beds containing adsorbents
known in the art for removal of moisture from gases.
[0071] The dried, compressed, purified flue gas stream 67 is then
cooled at a heat exchanger 10. Exchanger 10 may be a multi-stream
type heat exchanger adapted and configured to exchange heat between
a plurality of streams. Typically, the multi-stream heat exchanger
is a brazed aluminum plate exchanger having multiple parallel cores
allowing it to cool/heat the plurality of streams. Alternatively,
exchanger 10 could be a combination of several smaller heat
exchangers not necessarily exchanging heat between each of the
streams illustrated. A combination of several smaller heat
exchangers is useful for segregation of higher pressure streams
from low pressure streams.
[0072] If several smaller heat exchangers are utilized instead of a
multi-stream heat exchanger (such as illustrated in FIGS. 2-3),
each particular heat exchanger will exchange heat between less than
all of the streams illustrated. In this case, it should be noted
that, with regard to all heating or cooling steps described and/or
illustrated, the skilled artisan will recognize that selection of
which stream or streams are used to cool another stream or streams
at a particular heat exchanger is well within the knowledge of a
chemical engineer in the field of industrial gases.
[0073] With continued reference to FIG. 2, the cold, dried,
compressed, purified flue gas stream 68 is fed to a gas separation
membrane unit 4. As described above, the membranes of the gas
separation membrane unit 4 allow selective permeation to form a low
pressure CO.sub.2 enriched permeate stream 57 and a CO.sub.2
depleted stream non-permeate stream 58. The gas separation
membranes of unit 4 may be operated at ambient or sub-ambient
temperature as described above.
[0074] The CO.sub.2 enriched permeate gas 57 is re-compressed to
about 6-30 bar in compressor 5. Compressor 5 also typically
includes water cooling of stream 57 where the thus-heated water may
be used as preheated boiler feed water. The water cooling of stream
57 also allows further water knock-out, but additional
adsorbent-based drying may be included, if needed. The dried and
compressed CO.sub.2 enriched stream 60, having a concentration of
>60% vol CO.sub.2, is cooled in exchanger 10 to partially
condense the CO.sub.2.
[0075] The gaseous and liquid CO.sub.2 phases are separated in
phase separator 12. As shown in FIG. 2, phase separator 12 is a one
pot phase separation unit producing a high purity, liquid CO.sub.2
stream 68 and a cold vent stream 62. The pressure of the high
purity, liquid CO.sub.2 stream 68 is boosted to about 60-150 bar by
a cryo-pump 14 and then warmed/vaporized at exchanger 10 to form
high purity (>95% vol CO.sub.2) product gas stream 59.
[0076] The cold vent stream 62 is passed through exchanger 10 and
is optionally partially expanded in expander 15 to match the
pressure of stream 67. After heat exchange and optional partial
expansion, stream 62 is combined with stream 67.
[0077] The membrane residue stream 58 is warmed at exchanger 10 and
fed to a PSA unit. FIG. 2 illustrates a PSA unit with four
adsorbent bed columns 71, 72, 73, 74. However, the PSA unit is not
limited to such a configuration. Rather, it may be configured
according to any other schemes known in the field of
adsorbent-based gas separation taking into consideration capital
cost vs. capture efficiency trade-offs. For example, in FIG. 2 the
adsorbent bed columns 71, 72, 73, 74 cycle through four modes of
operation: [0078] a) CO.sub.2 adsorption mode 71, [0079] b) let
down of pressure in CO.sub.2 blow down mode 72, [0080] c)
regeneration of adsorbent by desorption with air 73, and [0081] d)
using warmed stream 58, repressurization 74.
[0082] With continued reference to FIG. 2, CO.sub.2 is selectively
adsorbed from warmed stream 58 by the adsorbent in column 71. A
further CO.sub.2 depleted (10 ppm-4%) vent gas is expanded at
expander 75 to provide a cold, expanded, CO.sub.2-depleted stream
64. The cold, expanded, CO.sub.2-depleted stream 64 is passed
through exchanger 10 to provide the necessary cold energy (i.e.,
for removal of enthalpy) to cool stream 67 for sub-ambient membrane
operation and also to partially condense stream 60. Depending on
the available pressure and flow rate of stream 64 downstream of
exchanger 10, it may be heated at heat exchanger 76 and then
further expanded at turbo-expander 8 for energy recovery and vented
as inert vent gas 65.
[0083] The pressure in column 72 is let down through venting to
produce CO.sub.2 blow-down stream 69. CO.sub.2 blow-down stream 69
has a CO.sub.2 concentration equal to or higher than that of stream
58 and is fed to the suction inlet of compressor 5. In the event
that CO.sub.2 blow-down stream 69 has a CO.sub.2 concentration
lower than that of stream 58, as shown by the dotted line, it may
instead be fed to the suction inlet of compressor 3.
[0084] Air stream 63 at close to ambient pressure flows through
column 73 to desorb CO.sub.2. Some degree of moisture may remain
adsorbed on adsorbent in column 73 after CO.sub.2 desorption. In
order to more effectively desorb that moisture, a final portion of
the air of stream 63 may either be dried (e.g., with zeolite 3A) or
pre-heated upstream of the PSA unit. The CO.sub.2-enriched air
stream 66 is fed to combustor 1 as described above.
[0085] Column 74 is pressurized with warmed stream 58. At the end
of this step, the adsorbent is in position to begin the adsorption
cycle again. Thus, in the next adsorption cycle, the columns 71,
72, 73, 74 are operated in the following modes: [0086] e) CO.sub.2
adsorption mode in column 74, [0087] f) let down of pressure in
CO.sub.2 blow down mode in column 71, [0088] g) regeneration of
adsorbent by desorption with air in column 72, and [0089] h) using
stream 58, repressurization in column 73.
[0090] The columns 71, 72, 73, 74 are subsequently operated in the
following modes: [0091] a) CO.sub.2 adsorption mode in column 73,
[0092] b) let down of pressure in CO.sub.2 blow down mode in column
74, [0093] c) regeneration of adsorbent by desorption with air in
column 71, and [0094] d) using stream 58, repressurization in
column 72.
[0095] The columns 71, 72, 73, 74 are subsequently operated in the
following modes: [0096] a) CO.sub.2 adsorption mode in column 72,
[0097] b) let down of pressure in CO.sub.2 blow down mode in column
73, [0098] c) regeneration of adsorbent by desorption with air in
column 74, and [0099] d) using stream 58, repressurization in
column 71.
[0100] Subsequently, operation of the columns 71, 72, 73, 74
returns to the first above-described cycle for the following modes:
[0101] a) CO.sub.2 adsorption mode in column 71, [0102] b) let down
of pressure in CO.sub.2 blow down mode in column 72, [0103] c)
regeneration of adsorbent by desorption with air in column 73, and
[0104] d) using stream 58, repressurization in column 74.
[0105] As shown in FIG. 3, another embodiment also includes
sub-ambient membrane separation and expansion of a non-permeate
stream downstream of PSA separation. The embodiment of FIG. 3 is
the same as FIG. 2 except for the following differences.
[0106] The further CO.sub.2-depleted vent gas 74 from column 71 is
not expanded for purposes of providing the necessary cold energy
for cooling the combination of streams 62 and 67 and for partial
condensation of stream 60. Rather, stream 74 is heated at heat
exchanger 76 and then further expanded at turbo-expander 8 for
energy recovery and vented as inert vent gas 65.
[0107] Also, after passing through exchanger 10 immediately
downstream of the gas separation membrane unit 4, the non-permeate
stream 58 is expanded at expander 76. The now-cold, expanded
non-permeate stream 58 is passed through exchanger 10 in order to
provide the necessary cold energy for cooling stream 67 and for
partial condensation of stream 60, prior stream 58 being fed to
column 71. In the embodiment of FIG. 3, the adsorption of CO.sub.2
from stream 58 in column 71 takes place at a lower pressure and
temperature than in the embodiment of FIG. 2.
[0108] While the embodiments of FIGS. 2 and 3 show one phase
separator 12 for effecting separation of the partially liquefied
stream 60 into vent gas stream 62 and CO.sub.2 product 59, other
schemes and apparatuses may be used for this separation. For
example, instead of a single phase separator 12 (as in FIGS. 2 and
3), FIG. 4 includes two phase separators 12a, 12b. The embodiment
of FIG. 4 can be thought of as a variation of the embodiment of
FIG. 2 or a variation of the embodiment of FIG. 3 where all
like-numbered reference characters denote a same apparatus or
stream.
[0109] As described above, permeate stream 57 is compressed and
partially condensed by compressor 5 and exchanger 10 to produce
stream 60. Instead of being received in phase separator 12 (as in
FIGS. 2 and 3), stream 60 is received in a first phase separator 12
of two in-series phase separators 12a, 12b. The gaseous overhead
from phase separator 12a exits as stream 62a, is partially expanded
across a Joule-Thomson valve, further cooled at exchanger 10, and
partially condensed in phase separator 12b. The resulting vent gas
stream 62b from phase separator 12b is optionally further expanded
in expander 13b to provide vent gas stream 62.
[0110] The bottom CO.sub.2-rich liquids exiting phase separators
12a, 12b is combined to provide high purity liquid CO.sub.2 stream
68. The pressure of stream 68 is boosted at cryo-pump 14 and then
vaporized at exchanger to form gaseous CO.sub.2 product stream
59.
[0111] As another example of a different scheme or apparatus for
achieving separation of the partially condensed stream 60, FIG. 5
includes two phase separators 12a, 12b plus a distillation column.
The embodiment of FIG. 5 can be thought of as a variation of the
embodiment of FIG. 2 or a variation of the embodiment of FIG. 3
where all like-numbered reference characters denote a same
apparatus or stream.
[0112] As explained above, permeate stream 57 is compressed and
partially condensed by compressor 5 and exchanger 10 to produce
stream 60. Instead of being received in phase separator 12 (as in
FIGS. 2 and 3), stream 60 is received in a first phase separator 12
of two in-series phase separators 12a, 12b. The gaseous overhead
from phase separator 12a exits as stream 62a, is partially expanded
across a Joule-Thomson valve, further cooled at exchanger 10, and
partially condensed in phase separator 12b. The resulting vent gas
stream 62b from phase separator 12b is optionally further expanded
in expander 13b.
[0113] The bottom CO.sub.2-rich liquid exits phase separators 12a,
12b as streams 68a, 68b. Streams 68a, 68b are optionally expanded
at Joule-Thomson valves 18a, 18b and fed to distillation column 16.
CO.sub.2-deficient vapor exits from a top of column 16 as vapor
stream 18 and high purity liquid CO.sub.2 exits a bottom of column
16 as high purity liquid CO.sub.2 stream 68. Vapor stream 18 is
combined with vent gas stream 62b to form CO.sub.2-depleted vent
gas 62. The pressure stream 68 is boosted at cryo-pump 14 and then
vaporized at exchanger to form gaseous CO.sub.2 product stream
59.
[0114] Suitable materials for use in the gas separation membranes
include polymeric materials having a CO.sub.2 permeance is >100
GPU and a CO.sub.2/N.sub.2 selectivity >20 at the selected
operational temperature and pressure. A variety of materials
satisfying these criteria are well-known to those skilled in the
art of gas separation membranes. For sub-ambient operation of the
membranes, suitable polymeric materials exhibit a CO.sub.2
solubility at 35.degree. C. and 10 bar pressure of >0.03
[(cm.sup.3 of CO.sub.2 at STP)/(cm.sup.3 of polymeric
material)(cmHg)] and a glass transition temperature of
>210.degree. C. Particular polymeric materials meeting these
requirements are disclosed in U.S. Pat. No. 8,617,292, the contents
of which are incorporated herein by reference.
[0115] The skilled artisan in the field of gas separation will
recognize that there is a wide variety of adsorbents known as
effective for separating CO.sub.2 from CO.sub.2-containing gas
mixtures through adsorption and the details of such adsorbents need
not be replicated herein. The skilled artisan will similarly
recognize that there is a wide variety of PSA techniques known as
effective for separating gases from gas mixtures and the details of
such adsorbents need not be replicated herein. Thus, the invention
should be considered to be limited to the particular PSA technique
described above with regard to FIGS. 2 and 3
[0116] While the invention has been described in conjunction with
specific embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications, and
variations as fall within the spirit and broad scope of the
appended claims. The present invention may suitably comprise,
consist or consist essentially of the elements disclosed and may be
practiced in the absence of an element not disclosed. Furthermore,
if there is language referring to order, such as first and second,
it should be understood in an exemplary sense and not in a limiting
sense. For example, it can be recognized by those skilled in the
art that certain steps can be combined into a single step.
[0117] The singular forms "a", "an" and "the" include plural
referents, unless the context clearly dictates otherwise.
[0118] "Comprising" in a claim is an open transitional term which
means the subsequently identified claim elements are a nonexclusive
listing i.e. anything else may be additionally included and remain
within the scope of "comprising." "Comprising" is defined herein as
necessarily encompassing the more limited transitional terms
"consisting essentially of" and "consisting of"; "comprising" may
therefore be replaced by "consisting essentially of" or "consisting
of" and remain within the expressly defined scope of
"comprising".
[0119] "Providing" in a claim is defined to mean furnishing,
supplying, making available, or preparing something. The step may
be performed by any actor in the absence of express language in the
claim to the contrary.
[0120] Optional or optionally means that the subsequently described
event or circumstances may or may not occur. The description
includes instances where the event or circumstance occurs and
instances where it does not occur.
[0121] Ranges may be expressed herein as from about one particular
value, and/or to about another particular value. When such a range
is expressed, it is to be understood that another embodiment is
from the one particular value and/or to the other particular value,
along with all combinations within said range.
[0122] All references identified herein are each hereby
incorporated by reference into this application in their
entireties, as well as for the specific information for which each
is cited.
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