U.S. patent application number 13/414132 was filed with the patent office on 2012-09-13 for system and process for the physical absorption of carbon dioxide from a flue gas stream.
This patent application is currently assigned to ALSTOM TECHNOLOGY LTD.. Invention is credited to Jean-Marc G. Amann, Andre Burdet, Gianfranco L. Guidati, Viktoria Von Zedtwitz-Nikulshyna.
Application Number | 20120227440 13/414132 |
Document ID | / |
Family ID | 46794271 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227440 |
Kind Code |
A1 |
Guidati; Gianfranco L. ; et
al. |
September 13, 2012 |
System And Process For The Physical Absorption of Carbon Dioxide
From a Flue Gas Stream
Abstract
Disclosed herein is a system comprising a first heat exchanger;
the first heat exchanger being operative to reduce a temperature of
a carbon dioxide rich flue gas stream to about -100 to about -60 C;
an absorber; the absorber being located downstream of the first
heat exchanger; wherein the absorber facilitates contact between
the flue gas stream and a solvent to form a carbon dioxide rich
solvent stream; the solvent being operative to selectively absorb
carbon dioxide over other gases present in the flue gas stream; and
a valve; the valve being located downstream of the absorber; the
valve being operative to reduce a pressure on the carbon dioxide
rich solvent stream to produce carbon dioxide and a lean carbon
dioxide solvent stream.
Inventors: |
Guidati; Gianfranco L.;
(Zurich, CH) ; Amann; Jean-Marc G.; (Vaxjo,
SE) ; Von Zedtwitz-Nikulshyna; Viktoria; (Zurich,
CH) ; Burdet; Andre; (Savigny, CH) |
Assignee: |
ALSTOM TECHNOLOGY LTD.
Baden
CH
|
Family ID: |
46794271 |
Appl. No.: |
13/414132 |
Filed: |
March 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61451278 |
Mar 10, 2011 |
|
|
|
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
B01D 2252/202 20130101;
B01D 2258/0283 20130101; Y02C 20/40 20200801; B01D 53/1425
20130101; Y02A 50/20 20180101; B01D 2252/2021 20130101; Y02C 10/06
20130101; Y02A 50/2342 20180101; B01D 53/1475 20130101 |
Class at
Publication: |
62/617 |
International
Class: |
F25J 3/08 20060101
F25J003/08 |
Claims
1. A system comprising: a first heat exchanger; the first heat
exchanger being operative to reduce a temperature of a carbon
dioxide rich flue gas stream to about -100 to about -60.degree. C.;
an absorber; the absorber being located downstream of the first
heat exchanger; wherein the absorber facilitates contact between
the flue gas stream and a solvent to form a carbon dioxide rich
solvent stream; the solvent being operative to selectively absorb
carbon dioxide over other gases present in the flue gas stream; and
a valve; the valve being located downstream of the absorber; the
valve being operative to reduce a pressure on the carbon dioxide
rich solvent stream to produce carbon dioxide and a lean carbon
dioxide solvent stream.
2. The system of claim 1, further comprising a flash tank; the
flash tank being operative to facilitate a separation of the carbon
dioxide from the lean carbon dioxide solvent stream.
3. The system of claim 2, where the lean carbon dioxide solvent
stream after separation from the carbon dioxide is recycled to the
absorber.
4. The system of claim 2, where the carbon dioxide after separation
from the lean carbon dioxide solvent stream is discharged to an
adiabatic compressor and to a intercooled compressor.
5. The system of claim 2, where the carbon dioxide after separation
from the lean carbon dioxide solvent stream is sequestered.
6. The system of claim 1, further comprising a first active cooling
system located downstream of the first heat exchanger; the first
active cooling system comprising a second heat exchanger and a
compressor in fluid communication with one another and where the
first active cooling system is operative to reduce the temperature
of the carbon dioxide rich flue gas stream.
7. The system of claim 1, further comprising a second active
cooling system located downstream of the first heat exchanger; the
second active cooling system comprising a second heat exchanger and
a compressor in fluid communication with one another and where the
second active cooling system is operative to reduce the temperature
of the lean carbon dioxide solvent stream.
8. The system of claim 2, further comprising a plurality of
throttle valves, flash tanks and adiabatic compressors to separate
the lean carbon dioxide solvent stream from the carbon dioxide.
9. The system of claim 1, wherein the solvent is an alcohol.
10. The system of claim 9, where the alcohol is ethanol, methanol,
propanol, butanol, or a combination comprising at least one of the
foregoing.
11. A method for capture of carbon dioxide from a flue gas stream,
the process comprising: receiving a carbon dioxide rich flue gas
stream from an emitter; the carbon dioxide rich flue gas stream
being at the pressure and temperature of the emitter; refrigerating
the carbon dioxide rich flue gas stream to a pressure of greater
than or equal to about 101.325 kPa and a temperature of about
0.degree. C. to about the melting point of carbon dioxide for a
given molar concentration of carbon dioxide within the carbon
dioxide rich flue gas stream; contacting the refrigerated carbon
dioxide rich flue gas stream with a lean liquid carbon dioxide
solvent stream; the lean liquid carbon dioxide solvent stream
having a higher solubility for carbon dioxide than of other gases
present in the carbon dioxide rich flue gas stream; absorbing
carbon dioxide with a liquid solvent to provide a carbon dioxide
rich solvent stream and a lean carbon dioxide flue gas stream; and
decreasing pressure of the carbon dioxide rich solvent stream to
provide the lean liquid carbon dioxide solvent stream and carbon
dioxide gas.
12. The method of claim 11, wherein the temperature to which the
carbon dioxide rich flue gas stream is refrigerated is between
about -100 to -60.degree. C.
13. The method of claim 11, wherein the refrigerating comprises
cooling the carbon dioxide rich glue gas stream using the lean
carbon dioxide flue gas stream.
14. The method of claim 11, further comprising adiabatically
compressing the carbon dioxide gas.
15. The method of claim 14, wherein the adiabatic compression is
performed using an axial compressor.
16. The method of claim 11, wherein decreasing pressure of the
carbon dioxide rich solvent stream is performed using a valve and a
flash tank.
17. The method of claim 11, wherein decreasing pressure of the
carbon dioxide rich solvent stream is performed in a series of
pressure reduction stages.
18. The method of claim 17, wherein each pressure reduction stage
includes a valve and a flash tank or a turbine and a flash
tank.
19. The method of claim 11, wherein at least one of the carbon
dioxide rich flue gas stream and the carbon dioxide lean solvent
stream is cooled by an active cooling loop.
20. The method of claim 11, wherein the carbon dioxide rich flue
gas stream is created by one of a fossil-fired power plant, a
bio-fuel fired power plant or an industrial process.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This reference claims priority to U.S. Provisional
Application No. 61/451,278 filed on Mar. 10, 2011, the entire
contents of which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] This disclosure relates to a system and to a process for the
physical absorption of carbon dioxide from a flue gas stream. In
particular, this disclosure relates to a method and system for the
physical absorption of carbon dioxide (CO.sub.2) from a process gas
stream using a solvent.
BACKGROUND
[0003] In the combustion of a fuel (e.g., coal, oil, peat, waste,
biofuel, natural gas, or the like) in combustion plants used for
the generation of power or for the production of materials such as
cement, steel or glass, or the like, a stream of hot flue gas (also
sometimes known as process gas) is generated. Such a hot flue gas
contains, among other components, carbon dioxide (CO.sub.2). The
negative environmental effects of releasing carbon dioxide to the
atmosphere have been widely recognized, and have resulted in the
development of processes adapted for removing carbon dioxide from
the hot flue gas using a liquid solvent to absorb the carbon
dioxide from the gas.
[0004] While such processes are believed to be effective, there
remains a need to reduce the power utilized to operate the system
(so called `parasitic power`), and to reduce the expense and
environmental impact of the solvent caused by solvent loss.
SUMMARY
[0005] Disclosed herein is a system comprising a first heat
exchanger; the first heat exchanger being operative to reduce a
temperature of a carbon dioxide rich flue gas stream to about -100
to about -60.degree. C.; an absorber; the absorber being located
downstream of the first heat exchanger; wherein the absorber
facilitates contact between the flue gas stream and a solvent to
form a carbon dioxide rich solvent stream; the solvent being
operative to selectively absorb carbon dioxide over other gases
present in the flue gas stream; and a valve; the valve being
located downstream of the absorber; the valve being operative to
reduce a pressure on the carbon dioxide rich solvent stream to
produce carbon dioxide and a lean carbon dioxide solvent
stream.
[0006] Disclosed herein is a method for capture of carbon dioxide
from a flue gas stream, the process comprising receiving a carbon
dioxide rich flue gas stream from an emitter; the carbon dioxide
rich flue gas stream being at the pressure and temperature of the
emitter; refrigerating the carbon dioxide rich flue gas stream to a
pressure of greater than or equal to about 101.325 kPa and a
temperature of about 0.degree. C. to about the melting point of
carbon dioxide for a given molar concentration of carbon dioxide
within the carbon dioxide rich flue gas stream; contacting the
refrigerated carbon dioxide rich flue gas stream with a lean liquid
carbon dioxide solvent stream; the lean liquid carbon dioxide
solvent stream having a higher solubility for carbon dioxide than
of other gases present in the carbon dioxide rich flue gas stream;
absorbing carbon dioxide with a liquid solvent to provide a carbon
dioxide rich solvent stream and a lean carbon dioxide flue gas
stream; and decreasing pressure of the carbon dioxide rich solvent
stream to provide the lean liquid carbon dioxide solvent stream and
carbon dioxide gas.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 depicts an exemplary system for capturing carbon
dioxide from a flue gas stream; and
[0008] FIG. 2 schematically depicts an exemplary multi-stage
desorption system that may be used in the system of FIG. 1.
DETAILED DESCRIPTION
[0009] Disclosed herein is a system and a method for treating a
solvent stream that contains carbon dioxide that is extracted from
a flue gas stream generated in a power plant. The system
advantageously comprises an absorber tower in fluid communication
with a flash tank, and a valve or a turbine. In the absorber tower
(hereinafter "absorber"), carbon dioxide is selectively absorbed
from a carbon dioxide rich flue gas stream into a solvent in an
absorber, while in the flash tank, the absorbed carbon dioxide is
released from the solvent and then discharged into a pipeline from
which it is then sequestered or used for other processes.
[0010] In one embodiment, the method for capture of the carbon
dioxide from a flue gas comprises refrigerating a carbon dioxide
rich flue gas (RFG) stream at a pressure of greater than or equal
to about 101.325 kPa and a temperature of about 0.degree. C. to
about the melting point of carbon dioxide for the given molar
concentration of carbon dioxide within the carbon dioxide rich flue
gas stream. The carbon dioxide rich flue gas stream emanating from
the emitter has a pressure greater than or equal to about
atmospheric pressure and a temperature of about 40 to about
60.degree. C. In one embodiment, the pressure of the refrigerated
carbon dioxide rich flue gas stream can be up to about 1000
kPa.
[0011] The method further comprises contacting the refrigerated
carbon dioxide rich flue stream with a lean carbon dioxide solvent
having a higher solubility for the carbon oxide (in the flue gas
stream) than for nitrogen and oxygen at the carbon dioxide rich
flue gas stream temperature. The contact between the carbon dioxide
rich flue gas stream and the solvent results in the extraction of
carbon dioxide from the carbon dioxide rich flue gas stream to
produce a lean carbon dioxide flue gas stream and a carbon dioxide
rich solvent stream. By decreasing the pressure of the carbon
dioxide rich solvent stream, the carbon dioxide is desorbed along
with the production of a lean carbon dioxide solvent stream. The
desorbed carbon dioxide is separately sequestered.
[0012] This system has a number of advantages because the solvent
selectively absorbs carbon dioxide from the flue gas, while not
interacting with other flue gas constituents such as nitric oxides
(NO.sub.x), sulfur oxides (SO.sub.x), and the like. The other flue
gas constituents such as NO.sub.x and SO.sub.x may be removed
upstream of the system if desired. This means that the stream of
carbon dioxide obtained after the separation from the solvent can
be advantageously used for other chemical purposes (other than
sequestration) if desired.
[0013] The FIG. 1 depicts a system 100 for removing carbon dioxide
from a carbon dioxide rich flue gas stream. The system comprises a
first heat exchanger 102 in fluid communication with a first active
cooling loop 200, an absorption-desorption loop 300 and a second
active cooling loop 400. The absorption-desorption loop comprises
an absorber 302, a valve 304, a flash tank 306, absorber 302, valve
304, a pump 314 and a compressor 308. The first heat exchanger 102
lies downstream of a flue gas emitter 110 at which the flue gas
stream (from which carbon dioxide is to be removed) is generated.
The flue gas stream may pass through other devices such as
scrubbers (not shown) where other contaminants such as oxygen,
nitrogen and particulate matter can be removed prior to entering
the first heat exchanger 102.
[0014] The first heat exchanger 102 lies upstream of the first
active cooling loop 200, the absorption-desorption loop 300 and the
second active cooling loop 400. The first heat exchanger 102 can
comprise any type of heat exchanger or sequence of heat exchangers
and serves to cool down the flue gas stream emanating from the flue
gas stream emitter 110 to a temperature proximate to the melting
point of carbon dioxide. With reference now to the exemplary
embodiment depicted in the FIG. 1, the carbon dioxide rich flue gas
stream 101 emanating from flue gas stream emitter 110 is cooled in
the first heat exchanger 102 by a counter current flow of a cooled
lean carbon dioxide flue gas stream 107 that emanates from the
absorber 302. The carbon dioxide rich flue gas stream 101 generally
contains about 3 to about 30 molar percent (mol %) carbon dioxide
based on the total weight of the carbon dioxide rich flue gas
stream 101. The lean carbon dioxide flue gas stream 107 generally
contains about 0 to about 10 mol % carbon dioxide based on the
total weight of the lean carbon dioxide flue gas stream 107. In one
embodiment, the first heat exchanger 102 reduces the temperature of
the flue gas stream from a temperature of about 40 to about
100.degree. C. to a temperature of about -60.degree. to about
-100.degree. C.
[0015] In one embodiment, the first heat exchanger 102 reduces the
temperature of the flue gas stream to a temperature slightly above
the melting temperature of carbon dioxide. In an exemplary
embodiment, it is desirable to reduce the temperature of the flue
gas stream to a temperature of -78 to -60.degree. C. In an
exemplary embodiment, for a molar carbon dioxide concentration of
14% in the flue gas stream, it is desirable for the carbon dioxide
rich flue gas temperature after emanating from the first heat
exchanger 102 to be about -100 to -60.degree. C.
[0016] The first heat exchanger 102 may not be a single unit but
may instead optionally comprise a collection of elements with the
purpose of cooling down the flue gas stream to the temperature
above the melting point of carbon dioxide. For example, the first
heat exchanger 102 may comprise one or more heat exchangers; direct
contact cooling (DCC) towers including the capability of (i)
removing SO.sub.x from the carbon dioxide rich flue gas (RFG)
stream using a pH-control system and of (ii) sub-zero cooling using
a brine solution; active cooling loops, auxiliary systems such as
fluid pumps, fans, and the like; and the capability to dry the
carbon dioxide rich flue gas through water removal in the DCC and
heat exchangers.
[0017] As noted above, the first heat exchanger 102 can be one of a
variety of heat exchangers. Examples of suitable heat exchangers
are a shell and tube heat exchanger, plate heat exchanger,
regenerative heat exchanger, adiabatic wheel heat exchanger, plate
fin heat exchanger, pillow plate heat exchanger, dynamic scraped
surface heat exchanger or a phase-change heat exchanger. One or
more of these heat exchangers may be used if desired. An exemplary
first heat exchanger 102 is a plate-fin heat exchanger.
[0018] After being cooled down in the first heat exchanger 102, the
carbon dioxide rich flue gas stream 103 is discharged to the first
active cooling loop 200. The first active cooling loop 200 is
optional. The first active cooling loop 200 is used only to further
cool down the carbon dioxide rich flue gas stream 103 when it does
not reach the low temperatures desired in the first heat exchanger
102. In one embodiment, the first active cooling loop 200 is used
when the mass flow of the lean carbon dioxide flue gas stream 107
is substantially less than the mass flow of the carbon dioxide rich
flue gas stream 101 and therefore cannot reduce the temperature of
the rich flue gas stream 103 to the desired value of -60 to
-100.degree. C. The representation of the active cooling system
200, as a single refrigeration loop, is symbolic and in reality may
be achieved using a standard low temperature, multi-stage cooling
cascade. For example, the first active cooling loop 200 may include
a heat exchanger 202 for exchanging heat from the carbon dioxide
rich flue gas stream to a refrigerant 210, a compressor 204 for
circulating the refrigerant 210 within the first active cooling
loop 200, a heat exchanger 206 for removing heat from the
refrigerant 210, and a throttle valve 208. Exemplary refrigerants
210 that can be used in the first active cooling loop 200 are
non-halogenated hydrocarbons such as methane, propane, propene,
iso-butane, or the like, ammonia, sulfur dioxide, or the like, or a
combination comprising at least one of the foregoing refrigerants.
While chlorofluorocarbons may also be used as refrigerants, it is
desirable to use environment-neutral refrigerants in the active
cooling loops 200 and 400 respectively.
[0019] The carbon dioxide rich flue gas stream 105 emanating from
the first active cooling loop 200 is then discharged to the
absorption-desorption loop 300. The absorption-desorption loop 300
comprises an absorber 302, a valve 304, a flash tank 306, an
adiabatic compressor 308, a heat exchanger 310 and an intercooled
compressor 312. The valve 304, the flash tank 306, the adiabatic
compressor 308, the heat exchanger 310 and the intercooled
compressor 312 each lie successively downstream of the absorber 302
and are in fluid communication with one another.
[0020] With regard now to the absorber 302 in the FIG. 1, the
carbon dioxide rich flue gas stream 105 enters from the bottom. The
carbon dioxide rich flue gas stream 105 flows up from the bottom of
the absorber and exits the absorber 302 from the top as the lean
carbon dioxide flue gas stream 107. In the absorber 302, the carbon
dioxide rich flue gas stream 105 contacts a solvent that
selectively absorbs carbon dioxide from the carbon dioxide rich
flue gas stream 105. The solvent can be any solvent that
selectively absorbs carbon dioxide from the flue gas stream 105 in
preference to other contaminants in the flue gas stream such as
nitrogen, oxygen, nitrogen oxides, sulfur oxides, particulate
matter, and the like. It is desirable for the solvent to have a low
melting point and a low vapor pressure at the operating (sub-zero)
temperatures. It is also desirable for the solvent to display a
minimal viscosity at operating (sub-zero) temperatures.
[0021] Suitable solvents for use in absorbing the carbon dioxide in
the absorber are alcohols. The alcohols can be monohydric,
polyhydric, aliphatic, alicyclic alcohols, or the like, or a
combination comprising at least one of the foregoing alcohols.
Examples of alcohols are methanol, ethanol, propanol, butanol,
pentanol, hexadecan-1-ol, ethane-1,2-diol, propane-1,2,3-triol,
butane-1,2,3,4-tetraol, pentane-1,2,3,4,5-pentol,
hexane-1,2,3,4,5,6-hexyl, heptane-1,2,3,4,5,6,7-heptol,
prop-2-ene-1-ol, 3,7-dimethylocta-2,6-dien-1-ol, prop-2-in-1-ol,
cyclohexane-1,2,3,4,5,6-hexol,
(2-propyl)-5-methyl-cyclohexane-1-ol, or the like, or a combination
comprising at least one of the foregoing alcohols. Exemplary
alcohols are methanol, ethanol, propanol, butanol, pentanol, or a
combination comprising at least one of the foregoing exemplary
alcohols.
[0022] As noted above, the carbon dioxide rich flue gas stream 105
enters the absorber tower 302 from the bottom, flows upwards during
which it contacts the solvent and leaves the absorber 302 at the
top. The solvent enters the absorber 302 from the top as a lean
carbon dioxide solvent stream 309 and leaves the absorber 302 from
the bottom as a carbon dioxide rich solvent stream 301.
[0023] The pressure within the absorber is maintained at
proximately atmospheric pressure during the contact between the
solvent and the carbon dioxide rich glue gas stream 105. During the
contact between the solvent and the carbon dioxide rich flue gas
stream 105 in the absorber 302, carbon dioxide and heat from the
flue gas stream is absorbed by the solvent. Carbon dioxide from the
flue gas stream 105 is absorbed by the solvent via physical
absorption. The heat of absorption, is mainly extracted by the
solvent that warms up during the process of absorption. The lean
carbon dioxide flue gas stream 107, which leaves the absorber 302
at the top is used to pre-cool the incoming carbon dioxide rich
glue gas stream 101 in the aforementioned first heat exchanger
102.
[0024] The carbon dioxide rich solvent stream 301 is collected at
the bottom of the absorber tower 2 and is passed to the desorption
portion of the absorption-desorption loop 300. The desorption
portion of the absorption-desorption loop 300 comprises a valve
304, the flash tank 306, a pump 314 and an adiabatic compressor
308.
[0025] The valve 304 is effective to the pressure of the carbon
dioxide rich solvent stream 301 to a level at which the carbon
dioxide extracted from the carbon dioxide rich flue gas stream 105
can be desorbed from the solvent and returns into gas phase within
the flash tank 306. The solvent enters the absorber 302 from the
top and leaves the absorber 302 from the bottom as a carbon dioxide
rich solvent stream 301. The valve 304 can be replaced with a
turbine to effect the same decrease in pressure which causes the
absorbed carbon dioxide to being desorbed from the solvent. The
turbine can be used when it is desirable to improve the cooling
effect of the expansion and produce power.
[0026] The reduced pressure is about 5 to about 500 times lower
(for a 90% carbon dioxide capture rate) than the original partial
pressure of the carbon dioxide in the carbon dioxide rich flue gas
stream 105. As noted above, the pressure in the absorber 302 is
around atmospheric pressure. The pressure of the carbon dioxide
rich solvent stream after the valve is therefore about 1/5.sup.th
atmosphere to about 1/500.sup.th atmosphere. In an exemplary
embodiment, for the aforementioned molar concentration of 14%
carbon dioxide in the flue gas stream 101 and 1 bar exhaust gas
pressure the pressure after the valve 304 would be about 0.010 bar.
Depending on the operating conditions, this pressure may also be
lower or higher.
[0027] The carbon dioxide lean solvent stream 303 and the carbon
dioxide released from the solvent is collected in the flash tank
306. The lean solvent, which is in liquid form is extracted from
the flash tank by a lean solvent pump 314 and discharged back to
the top of the absorber 302. The lean solvent pump 314 increases
the pressure of the solvent to the level that is desired at the top
of the absorber 314. The pressure at the top of the absorber 302 is
about 1 atmosphere or greater. In an exemplary embodiment, the
pressure of the solvent at the top of the absorber 302 is about 1
atmosphere.
[0028] The carbon dioxide gas desorbed from the solvent is drawn
from the flash tank 306 by an adiabatic compressor 308. The
adiabatic compressor 308 increases the pressure of the carbon gas
from about 0.010 bar to a level where the temperature of the gas is
above the temperature of available cooling water. Depending on the
specific conditions (flash tank 4 pressure, rich solvent
temperature) the exhaust pressure of the adiabatic carbon dioxide
compressor 308 may be up to about 1 bar, specifically about 0.001
to about 1 bar. In order to minimize the work needed to compress
the carbon dioxide to the pipeline pressure of about 100 bar, the
carbon dioxide gas leaving the adiabatic carbon dioxide compressor
308 may be cooled using cooling water in a heat exchanger 310.
Downstream of the heat exchanger 310, the pressure of the carbon
dioxide gas is raised in several steps in an intercooled compressor
312 to a desired pipeline pressure, where the carbon dioxide gas
may be transported for use or sequestration. In one embodiment,
this compression of the carbon dioxide gas may be similar to that
used in post-combustion carbon dioxide capture processes based on
chemical absorption and oxy-fuel processes.
[0029] In one embodiment, the desorption portion of the
absorption-desorption loop 300 may comprise a plurality of valves,
flash tanks and adiabatic carbon dioxide compressors with pressure
in each succeeding flash tank being less than the pressure of the
preceding flash tank. In other words, a flash tank that lies
downstream of a preceding flash tank has a lower pressure than that
of the preceding flash tank.
[0030] With reference now to the FIG. 2, a multistage desorption
system 500 comprises a first valve 502 in fluid communication with
a first flash tank 504, a second valve 506, a second flash tank
508, a third valve 510, a third flash tank 512, a first adiabatic
compressor 514, a second adiabatic compressor 516 and a third
adiabatic compressor 518. The adiabatic compressors 514, 516 and
518 are in mechanical communication with a motor. A first stage
desorption system comprises the first valve 502, a first flash tank
504 and the first adiabatic compressor 514 is in fluid
communication with a second stage desorption system comprising the
second valve 506, the second flash tank 508 and the second
adiabatic compressor 516 and a third desorption system comprising
the third valve 510, the third flash tank 512 and the third
adiabatic compressor 518. The pressure P1 of the carbon dioxide in
the first stage desorption system after the first valve 502 is
higher than the pressure P2 of the carbon dioxide in the second
stage desorption system after the second valve 506, which is in
turn greater than the pressure P3 of the carbon dioxide in the
third stage desorption system after the third valve 510. The carbon
dioxide released by the multistage desorption system 500 is
pressurized (as detailed above) in the intercooled compressor 312.
The carbon dioxide may also be cooled using cooling water in a heat
exchanger 310 that lies upstream of the intercooled compressor
312.
[0031] This multi-stage arrangement allows the system to collect as
much carbon dioxide as possible at a pressure greater than the
aforementioned minimum pressure of about 0.010 bar. This
arrangement also reduces the power consumption and the size and
costs of the adiabatic carbon dioxide compressor. While the FIG. 2
shows a possible arrangement with three pressure level stages, it
is contemplated that the number of pressure level stages may be
greater than 3 or less than 3 but greater than or equal to 1.
[0032] With reference now to the FIG. 1, it may be seen that a
second active cooling system 400 may optionally be used on the lean
solvent as well. The second active cooling system 400 is optional
and functions in much the same manner as the first active cooling
system 200. For example, the second active cooling loop 400 may
include a second heat exchanger 402 for exchanging heat from the
lean solvent stream 307 to a refrigerant 410, a compressor 404 for
circulating the refrigerant 410 within the second active cooling
loop 400, a heat exchanger 406 for removing heat from the
refrigerant 410, and a throttle valve 408. The second active loop
400 may be used to cool down the lean carbon dioxide solvent stream
309 to temperatures where it will most selectively extract carbon
dioxide from the carbon dioxide rich flue gas stream 105.
[0033] The disclosed process is advantageous in a variety of ways.
The power consumption of the current method of system 100 is
estimated to be low compared to other carbon dioxide capture
systems that use solvents which selectively extract carbon dioxide
from flue gas streams. This is because the carbon dioxide rich flue
gas stream 105 is at about atmospheric pressure during the
absorption stage (within absorber 302) no flue gas compression is
needed, and since the solvent is regenerated via expansion by
valve(s) 304 and flash tank(s) 306, the main power consuming
element of system 100 are the carbon dioxide compressors 308 and
312. Use of a high-efficiency axial compressor as carbon dioxide
compressor 308 can thus lead to low power consumption. Such a
compressor could be based on technology used in gas turbines.
[0034] In addition, the solvent losses in the method of system 100
are expected to be very low because of the low operation
temperature (e.g., a carbon dioxide rich flue gas stream
temperature of about -100 to -60.degree. C. in the absorber 302.
Furthermore, because the system 100 may be installed with minimal
changes to an existing carbon dioxide recovery system (e.g., no
need to install compressors to increase the pressure of the rich
flue gas stream), the system 10 can be installed on an existing
power plant without a long shut-down period.
[0035] It will be understood that, although the terms "first,"
"second," "third" etc. may be used herein to describe various
elements, components, regions, layers and/or sections, these
elements, components, regions, layers and/or sections should not be
limited by these terms. These terms are only used to distinguish
one element, component, region, layer or section from another
element, component, region, layer or section. Thus, "a first
element," "component," "region," "layer" or "section" discussed
below could be termed a second element, component, region, layer or
section without departing from the teachings herein.
[0036] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting. As
used herein, the singular forms "a," "an" and "the" are intended to
include the plural forms as well, unless the context clearly
indicates otherwise. It will be further understood that the terms
"comprises" and/or "comprising," or "includes" and/or "including"
when used in this specification, specify the presence of stated
features, regions, integers, steps, operations, elements, and/or
components, but do not preclude the presence or addition of one or
more other features, regions, integers, steps, operations,
elements, components, and/or groups thereof.
[0037] Furthermore, relative terms, such as "lower" or "bottom" and
"upper" or "top," may be used herein to describe one element's
relationship to other elements as illustrated in the Figures. It
will be understood that relative terms are intended to encompass
different orientations of the device in addition to the orientation
depicted in the Figures. For example, if the device in one of the
figures is turned over, elements described as being on the "lower"
side of other elements would then be oriented on "upper" sides of
the other elements. The exemplary term "lower," can therefore,
encompasses both an orientation of "lower" and "upper," depending
on the particular orientation of the figure. Similarly, if the
device in one of the figures is turned over, elements described as
"below" or "beneath" other elements would then be oriented "above"
the other elements. The exemplary terms "below" or "beneath" can,
therefore, encompass both an orientation of above and below.
[0038] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
disclosure belongs. It will be further understood that terms, such
as those defined in commonly used dictionaries, should be
interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and the present
disclosure, and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
[0039] Exemplary embodiments are described herein with reference to
cross section illustrations that are schematic illustrations of
idealized embodiments. As such, variations from the shapes of the
illustrations as a result, for example, of manufacturing techniques
and/or tolerances, are to be expected. Thus, embodiments described
herein should not be construed as limited to the particular shapes
of regions as illustrated herein but are to include deviations in
shapes that result, for example, from manufacturing. For example, a
region illustrated or described as flat may, typically, have rough
and/or nonlinear features. Moreover, sharp angles that are
illustrated may be rounded. Thus, the regions illustrated in the
figures are schematic in nature and their shapes are not intended
to illustrate the precise shape of a region and are not intended to
limit the scope of the present claims.
[0040] The term and/or is used herein to mean both "and" as well as
"or". For example, "A and/or B" is construed to mean A, B or A and
B.
[0041] The transition term "comprising" is inclusive of the
transition terms "consisting essentially of" and "consisting of"
and can be interchanged for "comprising".
[0042] While the invention has been described with reference to
various exemplary embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications may be made
to adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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