U.S. patent application number 12/158523 was filed with the patent office on 2008-12-11 for method and device for recovering carbon dioxide from fumes.
This patent application is currently assigned to GAZ DE FRANCE. Invention is credited to Joelle Gitton, Samuel Saysset.
Application Number | 20080302133 12/158523 |
Document ID | / |
Family ID | 36974704 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302133 |
Kind Code |
A1 |
Saysset; Samuel ; et
al. |
December 11, 2008 |
Method and Device for Recovering Carbon Dioxide from Fumes
Abstract
The method and the system for capturing the carbon dioxide
present in flue-gas implement a) a first cooler device (110, 120)
for cooling flue-gas and comprising at least one heat exchanger
(122) for eliminating a fraction of the water present in the
flue-gas by condensation; b) a flue-gas dehydration device (130);
c) a second cooler device (140) for cooling the flue-gas and
comprising at least one heat exchanger (141, 142) for bringing the
flue-gas to a temperature that causes anti-sublimation of the
carbon dioxide present in the flue-gas; d) a heater device (141,
142) in a closed enclosure for heating the solidified carbon
dioxide to cause it to melt; and e) a device (144) for drawing off
or pumping liquid and/or gaseous carbon dioxide to a thermally
insulated tank (150). The system further comprises an expander
device (152, 153) for expanding a portion of the recovered liquid
carbon dioxide to atmospheric pressure, and for reinjecting said
portion of the carbon dioxide into the flue-gas at the second
flue-gas cooler means (140).
Inventors: |
Saysset; Samuel; (Asnieres
sur Seine, FR) ; Gitton; Joelle; (Villemomble,
FR) |
Correspondence
Address: |
WEINGARTEN, SCHURGIN, GAGNEBIN & LEBOVICI LLP
TEN POST OFFICE SQUARE
BOSTON
MA
02109
US
|
Assignee: |
GAZ DE FRANCE
Paris
FR
|
Family ID: |
36974704 |
Appl. No.: |
12/158523 |
Filed: |
December 20, 2006 |
PCT Filed: |
December 20, 2006 |
PCT NO: |
PCT/FR2006/051400 |
371 Date: |
June 20, 2008 |
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
F25J 2215/04 20130101;
F25J 2205/20 20130101; F25J 2210/70 20130101; Y02C 10/12 20130101;
F25J 2270/904 20130101; Y02C 20/40 20200801; F25J 3/067 20130101;
B01D 2256/22 20130101; F25J 2220/82 20130101; B01D 2257/504
20130101; F25J 2270/02 20130101; Y02C 10/04 20130101; C10L 3/10
20130101; B01D 53/002 20130101; F25J 2210/62 20130101; F25J 2220/80
20130101; F25J 2290/60 20130101; F25J 2205/24 20130101; F25J 3/066
20130101; F25J 2220/84 20130101 |
Class at
Publication: |
62/617 |
International
Class: |
F25J 3/00 20060101
F25J003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2005 |
FR |
0513078 |
Claims
1. A method of capturing the carbon dioxide present in flue-gas,
the method comprising the following steps: a) first cooling of the
flue-gas in order to eliminate a fraction of the water present
therein by condensation; b) dehydrating the flue-gas in order to
eliminate the residual water; c) second cooling of the flue-gas by
heat exchange so as to bring them to a temperature such that carbon
dioxide passes directly from the gaseous state to the solid state
by anti-sublimation; d) after removing the flue-gas, heating the
solidified carbon dioxide in a closed enclosure up to the triple
point where a liquid phase appears; and e) drawing off or pumping
out the liquid and/or gaseous carbon dioxide to a thermally
insulated tank; the method being characterized in that a fraction
of the recovered liquid carbon dioxide is recycled, and after
expanding to atmospheric pressure, is reinjected during the second
cooling step in continuous or intermittent manner in order to be
mixed with the flue-gas previously delivered by the dehydration
step.
2. A method according to claim 1, characterized in that the
fraction of the recovered liquid carbon dioxide that is recycled is
reinjected during the second cooling step in the form of fine solid
particles.
3. A method according to claim 1, characterized in that the
fraction of the recovered liquid carbon dioxide that is recycled is
injected during the second cooling step into the inside of a heat
exchanger.
4. A method according to claim 1, characterized in that it further
comprises a step of pre-cooling the flue-gas prior to said first
cooling step, the pre-cooling step being performed by exchanging
heat with at least one of the fluids comprising the liquid water
recovered during the first cooling step and the flue-gas
dehydration step, and the non-condensable compounds from the
flue-gas that are recovered after said second cooling step.
5. A method according to claim 1, characterized in that the first
cooling of the flue-gas, the dehydration of the flue-gas, and the
second cooling of the flue-gas make use of heat exchange with the
flue-gas via cooling loops operating by heat exchange with the
liquefied natural gas that is present in a methane terminal for
regassification, and that is used as a cold source.
6. A method according to claim 5, characterized in that the first
cooling of the flue-gas and the dehydration of the flue-gas are
performed by exchanging heat with the flue-gas via at least one
cooling loop making use of glycol-containing water.
7. A method according to claim 5, characterized in that the second
cooling of flue-gas makes use of heat exchange with the flue-gas
via at least one cooling loop making use of methane or of
nitrogen.
8. A method according to claim 7, characterized in that the second
cooling of flue-gas makes use of heat exchange with the flue-gas
via at least one additional cooling loop making use of ethylene or
ethane.
9. A method according to claim 1, characterized in that the
dehydration of flue-gas includes a step of exchanging heat with the
non-condensable compounds from the flue-gas recovered after the
second cooling step.
10. A method according to claim 1, characterized in that the step
of dehydrating the flue-gas is performed discontinuously with
alternation between a step of cooling the flue-gas to solidify
water on the walls of a heat exchanger and a step of heating the
solidified water in order to enable it to be recovered in liquid
form.
11. A method according to claim 10, characterized in that the
solidified water is heated by exchanging heat with the flue-gas
prior to the flue-gas being cooled during the step of cooling
flue-gas with water being solidified.
12. A method according to claim 1, characterized in that the second
flue-gas cooling step for causing anti-sublimation of the carbon
dioxide, and the solidified carbon dioxide heating step are
performed discontinuously and in alternation.
13. A method according to claim 12, characterized in that the step
of heating the solidified carbon dioxide to the triple point at
which a liquid phase appears is performed by heat exchange with the
flue-gas prior to the flue-gas being cooled during the second
cooling step.
14. A method according to claim 1, characterized in that it further
includes a step of recovering sulfur oxides contained in the
flue-gas by anti-sublimation and reheating to the triple point
where a liquid phase of sulfur oxides appears.
15. A system for capturing carbon dioxide present in flue-gas, the
system comprising: a) first cooler means for cooling flue-gas and
comprising at least one heat exchanger for eliminating a fraction
of the water present in the flue-gas by condensation; b) flue-gas
dehydration means; c) second cooler means for cooling flue-gas and
comprising at least one heat exchanger for bringing the flue-gas to
a temperature that causes anti-sublimation of the carbon dioxide
present in the flue-gas; d) heater means for heating the solidified
carbon dioxide in a closed enclosure in order to cause it to melt;
and e) means for drawing off or pumping the liquid and/or gaseous
carbon dioxide to a thermally insulated tank; the system being
characterized in that it further comprises expander means for
expanding a fraction of the recovered liquid carbon dioxide to
atmospheric pressure and for reinjecting said fraction of the
carbon dioxide into the flue-gas at said second flue-gas cooler
means.
16. A system according to claim 15, characterized in that it
includes means for reinjecting said recovered fraction of the
liquid carbon dioxide in the form of fine solid particles into the
flue-gas.
17. A system according to claim 15, characterized in that the first
cooler means comprise a heat exchanger between the flue-gas and at
least one of the fluids comprising the liquid water recovered in
the first cooler means or in the flue-gas dehydration means, and
the non-condensable compounds of the flue-gas recovered at the
inlet to the second cooler means.
18. A system according to claim 15, characterized in that it
includes cooling loops using heat-transferring fluids flowing
firstly in heat exchangers present in a methane terminal for
exchanging heat with the liquefied natural gas subjected to a
regassification process, and secondly in heat exchangers placed in
at least one of the first cooler means, the dehydration means, and
the second cooler means in order to exchange heat with the
flue-gas, giving rise to capture of carbon dioxide.
19. A system according to claim 18, characterized in that it
includes at least one cooling loop using glycol-containing water as
its heat-transferring fluid and including at least one heat
exchanger disposed in the first cooler means to the dehydration
means.
20. A system according to claim 18, characterized in that it
includes at least one cooling loop using methane or nitrogen as its
heat-transferring fluid and including at least one heat exchanger
disposed in the second cooler means.
21. A system according to claim 20, characterized in that it
further includes at least one cooling loop using ethylene or ethane
as its heat-transferring fluid and including at least one heat
exchanger disposed in the second cooler means.
22. A system according to claim 15, characterized in that it
includes means for recovering non-condensable compounds from the
flue-gas at the outlet from the second cooler means, and means for
exchanging heat with at least one of the flue-gas dehydration
means.
23. A system according to claim 15, characterized in that the
flue-gas dehydration means comprise at least first and second
enclosures provided with heat exchangers and capable of receiving
flue-gas discontinuously so that each of them can act in turn to
cool flue-gas and solidify the water contained therein on the walls
of the corresponding enclosure, and to heat the solidified water in
order to enable it to be recovered in liquid form.
24. A system according to claim 15, characterized in that the
second flue-gas cooler means and said heater means comprise at
least first and second enclosures provided with heat exchangers and
capable of receiving flue-gas discontinuously in such a manner that
each of them in turn cools flue-gas with anti-sublimation of the
carbon dioxide that is deposited on the walls of the corresponding
enclosure, and heats the solidified carbon dioxide in order to
cause it to melt.
25. A system according to claim 15, characterized in that it
further comprises means for recovering sulfur oxides from said
heater means in a closed enclosure.
26. A method according to claim 2, characterized in that the
fraction of the recovered liquid carbon dioxide that is recycled is
injected during the second cooling step into the inside of a heat
exchanger; it further comprises a step of pre-cooling the flue-gas
prior to said first cooling step, the pre-cooling step being
performed by exchanging heat with at least one of the fluids
comprising the liquid water recovered during the first cooling step
and the flue-gas dehydration step, and the non-condensable
compounds from the flue-gas that are recovered after said second
cooling step; the first cooling of the flue-gas, the dehydration of
the flue-gas, and the second cooling of the flue-gas make use of
heat exchange with the flue-gas via cooling loops operating by heat
exchange with the liquefied natural gas that is present in a
methane terminal for regassification, and that is used as a cold
source; the first cooling of the flue-gas and the dehydration of
the flue-gas are performed by exchanging heat with the flue-gas via
at least one cooling loop making use of glycol-containing water;
the second cooling of flue-gas makes use of heat exchange with the
flue-gas via at least one cooling loop making use of methane or of
nitrogen; the second cooling of flue-gas makes use of heat exchange
with the flue-gas via at least one additional cooling loop making
use of ethylene or ethane; the dehydration of flue-gas includes a
step of exchanging heat with the non-condensable compounds from the
flue-gas recovered after the second cooling step; the step of
dehydrating the flue-gas is performed discontinuously with
alternation between a step of cooling the flue-gas to solidify
water on the walls of a heat exchanger and a step of heating the
solidified water in order to enable it to be recovered in liquid
form; the solidified water is heated by exchanging heat with the
flue-gas prior to the flue-gas being cooled during the step of
cooling flue-gas with water being solidified; the second flue-gas
cooling step for causing anti-sublimation of the carbon dioxide,
and the solidified carbon dioxide heating step are performed
discontinuously and in alternation; the step of heating the
solidified carbon dioxide to the triple point at which a liquid
phase appears is performed by heat exchange with the flue-gas prior
to the flue-gas being cooled during the second cooling step; and it
further includes a step of recovering sulfur oxides contained in
the flue-gas by anti-sublimation and reheating to the triple point
where a liquid phase of sulfur oxides appears.
27. A system according to claim 16, characterized in that the first
cooler means comprise a heat exchanger between the flue-gas and at
least one of the fluids comprising the liquid water recovered in
the first cooler means or in the flue-gas dehydration means, and
the non-condensable compounds of the flue-gas recovered at the
inlet to the second cooler means; it includes cooling loops using
heat-transferring fluids flowing firstly in heat exchangers present
in a methane terminal for exchanging heat with the liquefied
natural gas subjected to a regassification process, and secondly in
heat exchangers placed in at least one of the first cooler means,
the dehydration means, and the second cooler means in order to
exchange heat with the flue-gas, giving rise to capture of carbon
dioxide; it includes at least one cooling loop using
glycol-containing water as its heat-transferring fluid and
including at least one heat exchanger disposed in the first cooler
means to the dehydration means; it includes at least one cooling
loop using methane or nitrogen as its heat-transferring fluid and
including at least one heat exchanger disposed in the second cooler
means; it further includes at least one cooling loop using ethylene
or ethane as its heat-transferring fluid and including at least one
heat exchanger disposed in the second cooler means; it includes
means for recovering non-condensable compounds from the flue-gas at
the outlet from the second cooler means, and means for exchanging
heat with at least one of the flue-gas dehydration means; the
flue-gas dehydration means comprise at least first and second
enclosures provided with heat exchangers and capable of receiving
flue-gas discontinuously so that each of them can act in turn to
cool flue-gas and solidify the water contained therein on the walls
of the corresponding enclosure, and to heat the solidified water in
order to enable it to be recovered in liquid form; the second
flue-gas cooler means and said heater means comprise at least first
and second enclosures provided with heat exchangers and capable of
receiving flue-gas discontinuously in such a manner that each of
them in turn cools flue-gas with anti-sublimation of the carbon
dioxide that is deposited on the walls of the corresponding
enclosure, and heats the solidified carbon dioxide in order to
cause it to melt; and it further comprises means for recovering
sulfur oxides from said heater means in a closed enclosure.
Description
[0001] The present invention relates to a method and a system for
capturing the carbon dioxide (CO.sub.2) contained in flue-gas or in
other gaseous effluent coming from industrial installations.
[0002] Capturing carbon dioxide and storing it geologically
presents an opportunity for reducing the emission of
greenhouse-effect gases, in addition to efforts at improving energy
efficiency and inciting the use of non-fossil resources.
[0003] At present, the cost of capturing CO.sub.2 constitutes about
three-quarters of the total cost of the system for geologically
sequestering CO.sub.2, including capturing, transporting, and
storing CO.sub.2.
[0004] Furthermore, energy consumption represents about 50% of the
cost of capture.
[0005] In particular, amongst the technologies that can be
envisaged for capturing CO.sub.2, low-temperature or "cryogenic"
distillation suffers from the drawback of consuming a large amount
of energy in order to achieve low temperatures.
[0006] There thus exists a need to rationalize the operation of
CO.sub.2 capture in order to improve the effectiveness of that
operation and reduce its cost.
[0007] The term "anti-sublimation" is used below to designate the
physical phenomenon of solid condensation whereby a gas changes
state and passes directly into the solid phase without liquefaction
taking place, i.e. without passing via the liquid state.
Anti-sublimation thus constitutes the physical phenomenon that is
the inverse of sublimation which designates a body passing directly
from the solid state to the gaseous state without passing via the
liquid state.
[0008] Various methods and systems for capturing CO.sub.2 by
liquefaction or anti-sublimation have already been proposed.
[0009] When carbon dioxide is at a partial pressure of more than
5.18 bar, it is possible to obtain direct liquefaction of CO.sub.2
by cooling flue-gas. That type of method nevertheless presents the
drawback of requiring effluents to be available under pressure or
flue-gas to be compressed.
[0010] When CO.sub.2 is available at a partial pressure of less
than 5.18 bar, as is true of combustion gas, cooling the flue-gas
will lead to anti-sublimation of CO.sub.2. The solid carbon dioxide
can then be handled in solid form, e.g. after being separated in a
cyclone, or it can be sublimed prior to being subsequently
liquefied downstream, or else it can be melted directly merely by
being heated.
[0011] Document EP 1 355 716 B1 and patent application WO
2004/080558 disclose a method of extracting CO.sub.2 from flue-gas
by cooling and solidifying CO.sub.2 at atmospheric pressure by
extracting heat by means of fractioned distillation.
[0012] Nevertheless, in some circumstances, in particular for
flue-gas coming from a gas turbine or a gas boiler, the CO.sub.2
content of the flue-gas can be quite low, e.g. about 1% to 5%,
which implies a starting temperature for anti-sublimation at
atmospheric pressure that can be of the order of -110.degree. C. to
-120.degree. C.
[0013] Furthermore, this CO.sub.2 content in flue-gas decreases
with increasing target capture ratio.
[0014] When forming a solid from a gaseous phase it is also
observed that anti-sublimation is delayed at low temperature and at
low partial pressure, in particular with CO.sub.2. This phenomenon
gives rise to anti-sublimation of the compound at a temperature
lower than the temperature specified by thermodynamics.
[0015] Because of this phenomenon, in order to anti-sublime
CO.sub.2, it is therefore necessary either to cool the compound
below its thermodynamic anti-sublimation temperature, which amounts
to having an even lower operating temperature in the heat
exchanger, or else to increase the heat exchange surface area,
thereby increasing the amount of contact between the compound and
cold surfaces. Both of those two conditions increase the cost of
the method.
[0016] The present invention seeks to remedy the above-mentioned
drawbacks and to enable CO.sub.2 to be captured in a manner that is
effective, but at reduced cost, and with installations that are
simplified, and with efficiency that is potentially improved.
[0017] According to the invention, these objects are achieved by a
method of capturing the carbon dioxide present in flue-gas, the
method comprising the following steps:
[0018] a) first cooling of the flue-gas in order to eliminate a
fraction of the water present therein by condensation;
[0019] b) dehydrating the flue-gas in order to eliminate the
residual water;
[0020] c) second cooling of the flue-gas by heat exchange so as to
bring it to a temperature such that carbon dioxide passes directly
from the gaseous state to the solid state by anti-sublimation;
[0021] d) after removing the flue-gas, heating the solidified
carbon dioxide in a closed enclosure up to the triple point where a
liquid phase appears; and
[0022] e) drawing off or pumping out the liquid and/or gaseous
carbon dioxide to a thermally insulated tank;
[0023] the method being characterized in that a fraction of the
recovered liquid carbon dioxide is recycled, and after expanding to
atmospheric pressure, is reinjected during the second cooling step
in continuous or intermittent manner in order to be mixed with the
flue-gas previously delivered by the dehydration step.
[0024] In order to combat the delay in anti-sublimation, it is
possible to encourage the kinetics of the anti-sublimation process
by injecting CO.sub.2 crystals that perform a seeding function for
solid formation. Such fine solid particles constitute nucleation
centers on which gaseous CO.sub.2 solidifies. The reinjection can
take place within the heat exchanger, starting from the point where
the temperature of the flue-gas is close to the theoretical
anti-sublimation temperature.
[0025] The recovered fraction of the liquid carbon dioxide that is
recycled is thus reinjected during the second cooling step,
preferably in the form of fine solid particles, and also preferably
into the inside of a heat exchanger.
[0026] In a particular implementation, the method further comprises
a step of pre-cooling the flue-gas prior to said first cooling
step, the pre-cooling step being performed by exchanging heat with
at least one of the fluids comprising the liquid water recovered
during the first cooling step and the flue-gas dehydration step,
and the non-condensable compounds from the flue-gas that are
recovered after said second cooling step.
[0027] In a particular advantageous implementation, the first
cooling of the flue-gas, the dehydration of the flue-gas, and the
second cooling of the flue-gas make use of heat exchange with the
flue-gas via cooling loops operating by heat exchange with the
liquefied natural gas (LNG) that is present in a methane terminal
for regassification, and that is used as a cold source.
[0028] According to a particular characteristic, the first cooling
of the flue-gas and the dehydration of the flue-gas are performed
by exchanging heat with the flue-gas via at least one cooling loop
making use of glycol-containing water.
[0029] According to another particular characteristic, the second
cooling of flue-gas makes use of heat exchange with the flue-gas
via at least one cooling loop making use of methane or of
nitrogen.
[0030] Under such circumstances, according to yet another
particular characteristic, the second cooling of flue-gas makes use
of heat exchange with the flue-gas via at least one additional
cooling loop making use of ethylene or ethane.
[0031] When LNG is available at a methane terminal for regassifying
natural gas, making use of the LNG as a cold source is particularly
advantageous since the low temperature of the LNG is thus used
advantageously for purposes of industrial and energy optimization,
with the flue-gas from which the CO.sub.2 is to be extracted then
constituting the hot source for intermediate-fluid heat exchangers
that enable the LNG that is stored in liquid form at -161.degree.
C. and at a pressure of 80 bar to be regassified.
[0032] When an industrial installation that gives off CO.sub.2,
such as a fossil fuel fired power station is located close to a
methane terminal in which LNG is regassified, it is therefore
entirely appropriate to make use of the LNG as a cold source in the
operation of capturing CO.sub.2 from the combustion gas or from
gaseous effluents, by anti-sublimation at approximately atmospheric
pressure, followed by melting at a pressure of a few bar, which can
be obtained merely by heating the solid CO.sub.2.
[0033] The invention is applicable to any flue-gas from power
stations and other thermal installations (steel works, cement
works, . . . ) that make use of a variety of fossil fuels (natural
gas, coal, oil, . . . ) and that contain various concentrations of
CO.sub.2, even concentrations that are low and less than 1%.
[0034] Furthermore, by using various cooling loops involving
different fluids and producing staged cooling of the flue-gas, it
is possible to reduce very significantly the dimensions of the
pipes in the final cryogenic loop that involves very low
temperatures (e.g. using nitrogen), even if the distance between
the methane terminal and the CO.sub.2 capture installation is
several hundreds of meters or several kilometers.
[0035] The method of the invention may present various other
advantageous characteristics depending in different particular
implementations:
[0036] Flue-gas dehydration includes a step of exchanging heat with
the non-condensable compounds of the flue-gas recovered after the
second cooling step.
[0037] The flue-gas dehydration step is performed discontinuously,
alternating between a step of cooling the flue-gas to solidify
water on the walls of a heat exchanger, and a step of heating the
solidified water in order to enable it to be recovered in liquid
form.
[0038] The solidified water is heated by exchanging heat with
flue-gas, prior to gas being cooled during the step of cooling
flue-gas with solidification of water.
[0039] The second flue-gas cooling step for giving rise to
anti-sublimation of carbon dioxide, and the step of heating the
solidified carbon dioxide are performed discontinuously and in
alternation.
[0040] The step of heating the solidified carbon dioxide up to the
triple point where a liquid phase appears can be performed by
exchanging heat with the flue-gas prior to cooling it during the
second flue-gas cooling step.
[0041] The method further includes a step of recovering sulfur
oxides contained in the flue-gas by anti-sublimation and by heating
up to the triple point where a sulfur oxide liquid phase
appears.
[0042] The invention also provides a system for capturing carbon
dioxide present in flue-gas, the system comprising:
[0043] a) first cooler means for cooling flue-gas and comprising at
least one heat exchanger for eliminating a fraction of the water
present in the flue-gas by condensation;
[0044] b) flue-gas dehydration means;
[0045] c) second cooler means for cooling flue-gas and comprising
at least one heat exchanger for bringing the flue-gas to a
temperature that causes anti-sublimation of the carbon dioxide
present in the flue-gas;
[0046] d) heater means for heating the solidified carbon dioxide in
a closed enclosure in order to cause it to melt; and
[0047] e) means for drawing off or pumping the liquid and/or
gaseous carbon dioxide to a thermally insulated tank;
[0048] the system being characterized in that it further comprises
expander means for expanding a fraction of the recovered liquid
carbon dioxide to atmospheric pressure and for reinjecting said
fraction of the carbon dioxide into the flue-gas at said second
flue-gas cooler means. The system preferably further includes means
for reinjecting said recovered fraction of the liquid carbon
dioxide in the form of fine solid particles into the flue-gas.
[0049] In a particular embodiment, the first cooler means comprise
a heat exchanger between the flue-gas and at least one of the
fluids comprising the liquid water recovered in the first cooler
means or in the flue-gas dehydration means, and the non-condensable
compounds of the flue-gas recovered at the inlet to the second
cooler means.
[0050] In an advantageous application, the system of the invention
includes cooling loops using heat-transferring fluids flowing
firstly in heat exchangers present in a methane terminal for
exchanging heat with the liquefied natural gas subjected to a
regassification process, and secondly in heat exchangers placed in
at least one of the first cooler means, the dehydration means, and
the second cooler means in order to exchange heat with the
flue-gas, giving rise to capture of carbon dioxide.
[0051] According to a particular characteristic, the system
includes at least one cooling loop using glycol-containing water as
its heat-transferring fluid and including at least one heat
exchanger disposed in the first cooler means to the dehydration
means.
[0052] According to another particular characteristic, the system
includes at least one cooling loop using methane or nitrogen as its
heat-transferring fluid and including at least one heat exchanger
disposed in the second cooler means.
[0053] Under such circumstances, in a particular embodiment, the
system may further comprise at least one cooling loop using
ethylene or ethane as its heat-transferring fluid and including at
least one heat exchanger disposed in the second cooler means.
[0054] The system may comprise means for recovering non-condensable
compounds from the flue-gas at the outlet from the second cooler
means, and means for exchanging heat with at least one of the
flue-gas dehydration means.
[0055] In a particular embodiment, the flue-gas dehydration means
comprise at least first and second enclosures provided with heat
exchangers and capable of receiving flue-gas discontinuously so
that each of them can act in turn to cool flue-gas and solidify the
water contained therein on the walls of the corresponding
enclosure, and to heat the solidified water in order to enable it
to be recovered in liquid form.
[0056] According to another particular aspect of the invention, the
second flue-gas cooler means and said heater means comprise at
least first and second enclosures provided with heat exchangers and
capable of receiving flue-gas discontinuously in such a manner that
each of them in turn cools flue-gas with anti-sublimation of the
carbon dioxide that is deposited on the walls of the corresponding
enclosure, and heats the solidified carbon dioxide in order to
cause it to melt.
[0057] The system may also include means for recovering sulfur
oxides in the heater means in a closed enclosure.
[0058] Other characteristics and advantages of the invention from
the following description of particular embodiments, given with
reference to the accompanying drawings, in which:
[0059] FIG. 1 is a diagrammatic overall view of a system for
capturing CO.sub.2 by anti-sublimation in accordance with the
invention;
[0060] FIG. 2 is a detail view showing the principle of a unit for
dehydration by solidification/melting and suitable for
incorporation in the system of FIG. 1;
[0061] FIG. 3 is a diagrammatic view comparing the sizes of
cryogenic loops when using a single loop and when using two
loops;
[0062] FIG. 4 is a graph plotting gas-liquid equilibrium curves for
various compounds as a function of temperature and pressure;
and
[0063] FIG. 5 is a CO.sub.2 pressure-temperature diagram showing
how CO.sub.2 varies during a capture method of the invention.
[0064] An embodiment of the present invention is described with
reference to FIG. 1.
[0065] Nevertheless, reference is made initially to FIG. 5 which
shows the thermodynamic phenomenon that is used, namely
anti-sublimation of CO.sub.2 followed by compression/melting
obtained merely by heating solid CO.sub.2.
[0066] As mentioned above, this phenomenon is applicable to the
flue-gases from fuel-burning installations and power stations that
make use of a variety of fossil fuels (natural gas, coal, oil, . .
. ), the flue-gases containing varying concentrations of CO.sub.2
that may lie in the range less than 1% to concentrations of several
tens of percent.
[0067] Table 1 gives examples of typical compositions for gas
turbine flue-gases.
TABLE-US-00001 TABLE 1 Gas turbine flue-gas composition N.sub.2
H.sub.2O O.sub.2 CO.sub.2 Low molar composition, wet (%) 76 6 14 4
Low molar composition, dry (%) 81 -- 15 4
[0068] As can be seen, after water has been eliminated, the
flue-gas contains about 4% CO.sub.2 (at a partial pressure of 0.04
bar).
[0069] The flue-gas can then be cooled in a heat exchanger until
CO.sub.2 condenses as from -110.degree. C. (see horizontal dashed
line in FIG. 5).
[0070] The solid CO.sub.2 trapped in the heat exchanger can then be
heated and taken to the conditions of the CO.sub.2 triple point
where liquid CO.sub.2 can be eliminated so as to move the thermal
equilibrium in favor of producing liquid CO.sub.2 (see top
dashed-line curve in FIG. 5).
[0071] The temperature at which the anti-sublimation process begins
depends on the CO.sub.2 content of the flue-gas. Thus, it varies
over the range -78.5.degree. C. for pure CO.sub.2 at atmospheric
pressure, to -121.9.degree. C. for effluent containing CO.sub.2 at
a partial pressure of 0.01 bar (see Table 2).
TABLE-US-00002 TABLE 2 Temperatures at which the CO.sub.2
anti-sublimation process begins as a function of the CO.sub.2
contents of flue-gas at atmospheric pressure CO.sub.2 content 100
15 10 5 2 1 0.1 Anti- -78.5 -99.3 -103.1 -109.3 -116.7 -121.9
-136.7 subli- mation temper- ature (.degree. C.) Type of Coal- Gas
boiler Gas compo- fired turbine sition plant
[0072] In accordance with the invention, a fraction of the liquid
CO.sub.2 obtained at the outlet from the method is recycled by
being expanded until fine solid particles are formed in the last
heat exchanger so as to create nucleation centers.
[0073] This recycling enables the anti-sublimation heat exchanger
to be optimized in terms of exchange area and final operating
temperature.
[0074] FIG. 1 shows an advantageous example of an embodiment of the
invention in the context of capturing flue-gas produced by an
industrial installation 10. After cooling, e.g. in a conventional
cooling tower 20, the combustion gas is available at a temperature
of about 40.degree. C. at the inlet to the CO.sub.2 capture and
processing installation 110.
[0075] In the example of FIG. 1, the industrial installation 10 is
situated close to a methane terminal 200 (e.g. at a distance of the
order of a few hundreds of meters to a few kilometers), which
terminal 200 receives LNG e.g. at a temperature of -161.degree. C.
and at a pressure of 80 bar, via a line 201. The LNG passes through
a heat exchanger 203 that exchanges heat between the LNG and
heat-transferring fluids circulating through heat exchangers 204,
205 having cooling loops 210 and 220. At the outlet 202 from the
methane terminal, the natural gas continues the regassification
process. The regassified natural gas can be used for example to
feed the industrial installation 10, such as a gas-fired power
station, via a line 206.
[0076] The invention applies to capturing CO.sub.2 from the
combustion gas, however it can also be applied to capturing
CO.sub.2 from other gaseous effluents, for example synthesis gas
obtained in a hydrogen-production context.
[0077] The invention also makes it possible, by using the same
anti-sublimation method, to capture sulfur oxides (SO.sub.x) that
might be present in the flue-gas together with the CO.sub.2.
[0078] In the FIG. 1 installation, the flue-gas acts as a hot
source for the cooling loops 210, 220, while the LNG at
-161.degree. C. acts as a cold source.
[0079] The flue-gas delivered via the line 101 is cooled in several
stages.
[0080] In a cooling device 120 comprising a heat exchanger 122,
with a cooling loop 210, e.g. glycol-containing water, the
combustion gas is cooled from 40.degree. C. to 1.degree. C. so as
to cause a fraction 123 of the water present in the gas to condense
as a liquid (liquefaction) in the enclosure 121.
[0081] The condensed water 123 is removed via a pipe 124 and may be
sent to a heat exchanger 111, for example, in order to perform
pre-cooling of the flue-gas prior to its entry into the cooling
device 120. The water heated in the heat exchanger 111 serves to
bring the flue-gas temperature to 30.degree. C., for example, and
it is then removed via a line 113 at a temperature that is close to
ambient (30.degree. C.).
[0082] The flue-gas coming from the cooling device 120 is
introduced via a line 125 into a gas dehydration device 130.
[0083] It is necessary to dehydrate the gas in order to eliminate
residual water (about 0.6% water in the gas, assuming that the
vapor pressure of water at 1.degree. C. is 6.6 millibar
(mbar)).
[0084] The residual water can solidify and might therefore block
the installation downstream, and might then be found in the
captured CO.sub.2.
[0085] The dehydration operation can also be performed by using the
LNG from the methane terminal 200 as a cold source, e.g. in a heat
exchanger 133 possibly suitable for being inserted in the same
cooling loop 210 (e.g. using glycol-containing water) as the heat
exchanger 122.
[0086] The residual water can thus be solidified, e.g. at
-30.degree. C., on the walls of at least one (131) of the two
enclosures 131, 132 that operate discontinuously in alternation
(i.e. in batch mode).
[0087] When the water has solidified on the walls of one of the
enclosures 131, the gas is switched to the inlet of the other
enclosure or of one of the other enclosures 131 so as to cause
residual water to solidify in the same manner. At the same time,
the water that has solidified on the walls of the first enclosure
131 is heated, e.g. making use of the heat in the gas by causing it
to pass through the first enclosure 131 prior to penetrating into
the second enclosure 132 where water capture is to take place.
[0088] This discontinuous operation in alternation of the
enclosures 131 and 132 is shown in greater detail in FIG. 2.
[0089] In FIG. 2, it can thus be seen that water-saturated gas at
1.degree. C. arriving via the line 125 penetrates initially into
the enclosure 132 (in which the heat exchangers 133 and 134 are
deactivated) for the purpose of melting the water that has
solidified on the walls of that enclosure, with the liquid water
being removed via a tube 136. The gas is then conveyed via a pipe
126 to the capture enclosure 131 within which the heat exchangers
133 and 134 are activated so as to cool the gas and capture the
residual water which solidifies on the walls of the enclosure 131.
The gas then leaves via a pipe 135 to be taken to the CO.sub.2
capture stage. During the following alternation, the gas arriving
via the pipe 124 is switched to the path drawn in dashed lines in
FIG. 2 so as to penetrate initially into the enclosure 131, where
it causes the water to melt and be removed via the tube 136, and
from which the gas penetrates into the enclosure 132, where the
heat exchangers 133 and 134 are then activated so as to solidify
the residual water. The gas leaving the enclosure 132 is then
transferred by the pipe 135 to the following stage for CO.sub.2
capture.
[0090] In the enclosures 131, 132, it is possible to use a heat
exchanger 134 as described above, forming part of a heat exchange
cooling loop, e.g. using the LNG of a methane terminal as the cold
source. It is also possible to make use of a heat exchanger 134
having non-condensable gas (nitrogen, oxygen, . . . ) flowing
therethrough and recovered from the gas at the outlet 145 of the
CO.sub.2 capture process.
[0091] The non-condensable gas can likewise subsequently be
transferred to a heat exchanger 112 acting, like the heat exchanger
111, to pre-cool and eliminate condensed water in a stage 110
situated upstream from the cooler device 120 and the dehydration
device 130. The residual non-condensable gas (O.sub.2, N.sub.2, . .
. ) can then be rejected into the atmosphere via a line 114 at a
temperature of about 30.degree. C. (FIGS. 1 and 2).
[0092] The liquid water removed by the tubes 136 can be used, like
the water recovered by the pipe 124, for pre-cooling in the heat
exchanger 111.
[0093] The gas present in the pipe 135 at the outlet from the
dehydration stage 130 can present a temperature of about
-30.degree. C. and it penetrates into another cooler device 140
that may comprise one or more heat exchangers 143 forming part of
cooling loops such as the loop 220 using the LNG present in the
methane terminal 200 as a cold source.
[0094] The cooler device 140 comprises at least two enclosures 141,
142, each having a heat exchanger 143 forming part of the cooling
loop 220, together with means 144, 155 for drawing off or pumping
liquid and/or gaseous CO.sub.2, and possibly also sulfur
dioxide.
[0095] The enclosures 141, 142 operate in discontinuous manner in
alternation in turns (i.e. they operate in batch mode) for
capturing CO.sub.2 (and possibly SO.sub.2) by anti-sublimation and
then for causing it to melt. Operation is similar to that described
above with reference to FIG. 2 for capturing water.
[0096] Thus, after CO.sub.2 (or SO.sub.2) has been deposited on the
walls of the enclosure 141 in which the heat exchanger 143 is
active, the gas is switched to the enclosure 142. Within the
enclosure 141, the heat exchanger 143 is deactivated and energy
from the gas can be used to cause the temperature of the solid
CO.sub.2 to rise, e.g. from a temperature of -130.degree. C. to a
temperature of about -56.6.degree. C., with the CO.sub.2 having a
partial pressure of 5.18 bar, which corresponds to the triple point
where the liquid and gaseous phases appear and coexist
simultaneously (see FIG. 5). In order to shift the solid-liquid-gas
equilibrium, it suffices to withdraw or pump out the CO.sub.2 via a
pipe 144 and deliver it to a thermally lagged tank 150 from which
CO.sub.2 can be taken via a pipe 151 for being transported to a
temporary storage site, prior to being transported to and injected
into an old oil field. During the melting of CO.sub.2, e.g. in the
enclosure 141, the gas passing through the other enclosure 142
leads to CO.sub.2 being deposited by anti-sublimation in the
enclosure 142. The solidified CO.sub.2 can then be melted during
the following cycle of heating in the enclosure 142, while the
CO.sub.2 capture phenomenon takes place in the enclosure 141. The
process of capture by anti-sublimation followed by recovery merely
by melting sulfur dioxide present in the gas can be performed in a
manner entirely similar to that described above with reference to
CO.sub.2.
[0097] As mentioned above, an important characteristic of the
invention lies in the fact that a fraction of the liquid CO.sub.2
obtained on the line 144 at the outlet from the cooler device 140
and recovered in the tank 150 is recycled by a pipe 152 provided
with a valve 153 either (dashed line) to the pipe 135 feeding
dehydrated flue-gas to the inlet of the cooler device 140, or
preferably (continuous lines) directly to the enclosures 141 and
142 in order to create nucleation centers for the anti-sublimation
of CO.sub.2.
[0098] As a result, it is possible to optimize the dimensioning of
the cooling loop 220 operating with nitrogen or methane, the
dimensioning of an optional additional loop using ethylene or
ethane, and the dimensioning of the anti-sublimation heat
exchangers 142 and 141 in terms of heat exchange area or CO.sub.2
capture rate.
[0099] FIG. 4 plots gas/liquid equilibrium curves between
-200.degree. C. and -30.degree. C. for various compounds that can
be used as heat-transferring fluids in the cooling loops 210, 220.
These compounds are nitrogen, methane, ethylene, CO.sub.2, ethane,
hexofluoroethane, and propane (curves referenced 1 to 7
respectively).
[0100] By using different cooling loops 210, 220 that implement
different heat-transferring fluids and that lead to cooling in
stages, it is possible to reduce the size of the cryogenic loop
that uses nitrogen.
[0101] Thus, FIG. 3 shows relative to the size of an average
individual 50, the size of a single nitrogen cryogenic loop using a
pipe 31 for liquid nitrogen, and a pipe 32 for gaseous nitrogen
return.
[0102] On the assumption that the energy needed for capturing 0.600
kilowatt hours per kilogram (kWh/kg) of CO.sub.2 (which corresponds
to exhaust gas from a gas turbine with recovery of energy, water,
and non-condensables), the cooling power needed for capturing 320
(metric) tonnes (t) of CO.sub.2 per hour is 192 megawatts (MW). On
the basis of a nitrogen loop at 25 bar (-155.degree. C. on the
liquid side, and 30.degree. C. on the gas side), the flow rate of
nitrogen to be conveyed is more than one million normal cubic
meters per hour (Nm.sup.3/h), giving a pipe diameter of 0.40 meters
(m) for the pipe 31 on the liquid side assuming the speed of the
liquid is 10 meters per second (m/s), (or of 0.70 m if the speed of
the liquid is 3 m/s, for example), and a pipe diameter of 1.60 m
for the pipe 32 on the gas side (10 m/s). A nitrogen loop of such a
size can give rise to problems in operation (cryogenic fluid to be
kept cold) and in terms of investment, in particular over distances
of several kilometers.
[0103] In contrast, when use is made firstly of a cooling loop,
e.g. with glycol-containing water 210 having go-and-return pipes 41
and 42, and also a nitrogen cooling loop 220 comprising a pipe 43
on the liquid side and a pipe 44 on the gas side, the dimensions of
the various pipes, including the pipe 44 can be reduced.
[0104] As mentioned with reference to FIGS. 1 and 2, the flue-gas
are dehydrated by cooling them from 40.degree. C. to 1.degree. C.
so as to eliminate free water, and then to temperatures that are
low enough to achieve the desired water contents. In the example
described, the dehydration operation is performed by using a
glycol-containing water cooling loop 210 that enables -40.degree.
C. to be reached, depending on the glycol content (ethylene glycol,
propylene glycol).
[0105] Table 3 gives the water contents of the flue-gas and of the
captured CO.sub.2 as a function of the cooling temperature.
TABLE-US-00003 TABLE 3 Water contents of the flue-gas and of the
captured CO.sub.2 as a function of the cooling temperature and for
a capture rate of 100% Flue-gas cooling Water content of Water
content of temperature (.degree. C.) flue-gas (ppm) captured
CO.sub.2 (ppm) -30 490 1.3% -40 180 0.5% -50 60 1,650 -60 18 490
-70 5 130 -80 1 30 -90 0.1 5
[0106] With a dew point at -30.degree. C., the water content of the
flue-gas is thus 490 parts per million (ppm), i.e. about 5 grams
(g) of water per kilogram (kg) of captured CO.sub.2 (1.3%).
[0107] In order to avoid problems of corrosion and of hydrate
formation during transport and injection into storage, it is
preferable to dehydrate the flue-gas to a greater extent in order
to obtain a water content in the CO.sub.2 that is as low as 50
ppm.
[0108] For this purpose, the flue-gas can be cooled to about
-75.degree. C. by using an additional cooling loop in the gas
dehydration portion.
[0109] This additional cooling loop may be a loop using LNG as its
cold source and a heat-transferring fluid such as methane or
ethylene.
[0110] Nevertheless, and as shown in FIG. 1, this additional loop
is preferably a loop that makes use of the non-condensable gas
available at the outlet 145 from the anti-sublimation stage so as
to continue cooling the flue-gas in the heat exchanger 134 in order
to obtain a temperature of about -75.degree. C. at the outlet 135
from the dehydration device.
[0111] Table 4 gives numerical values for an example of a flue-gas
dehydration installation in a cycle that combines 800 MW of natural
gas, with a cooling power of 164 MW for performing dehydration,
shared between the heat exchanger 122 (99 MW) and the heat
exchanger 133 (65 MW). On the basis of a glycol-containing water
loop at 1 bar (-40.degree. C. cold side and 30.degree. C. hot
side), the flow rate of water that needs to be transported is about
2500 m.sup.3/h, giving a diameter of about 0.30 m for the pipes 41
and 42 in FIG. 3.
[0112] Table 4 gives the temperature, the pressure, and the flow
rate for nitrogen, oxygen, argon, CO.sub.2, and water at various
points in the installation of FIG. 1: [0113] 1: pipe 101 at the
inlet to the pre-cooler 110; [0114] 2: inlet pipe to the cooler
120; [0115] 3: inlet pipe 125 to the dehydrator 130; [0116] 4:
outlet pipe 135 from the dehydrator 130; [0117] 5: non-condensable
gas transfer pipe at the inlet to the heat exchanger 134; [0118] 6:
non-condensable gas transfer pipe at the inlet to the heat
exchanger 112; [0119] 7: non-condensable gas removal pipe at the
outlet 114 from the heat exchanger 112.
TABLE-US-00004 [0119] TABLE 4 1 2 3 4 5 6 7 Temperature (.degree.
C.) 40 24 1 -75 -90 -40 30 Pressure 1 1 1 1 1 1 1 Nitrogen (t/h)
4432 4432 4432 4432 4432 4432 4432 Oxygen (t/h) 9189 9189 9189 9189
9189 9189 9189 Argon (t/h) 75 75 75 75 75 75 75 CO.sub.2 (t/h) 320
320 320 320 0 0 0 Water (t/h) 233 233 23 2 0 0 0
[0120] The cooling power needed for cooling the flue-gas from
-75.degree. C. to -90.degree. C. and for CO.sub.2 anti-sublimation
(going from the vapor state at atmospheric pressure and -75.degree.
C., to the liquid state at the triple point) is 50 MW (comprising
21 MW for cooling the flue-gas from -75.degree. C. to -90.degree.
C., and 29 MW for CO.sub.2 anti-sublimation). On the basis of a
nitrogen loop at 25 bar (-155.degree. C. on the liquid side and
30.degree. C. on the gas side), the pipe diameter will be 0.20 m
for the pipe 43 situated on the liquid side if the flow speed of
the liquid is 10 m/s (or 0.30 m if the flow speed of the liquid is
3 m/s), and the diameter will be 0.80 m for the pipe 44 on the gas
side (10 m/s) (FIG. 3).
[0121] The dimensions of such a nitrogen cooling loop are thus
entirely acceptable for easy practical implementation.
* * * * *