U.S. patent application number 13/920735 was filed with the patent office on 2013-10-24 for method and system for removing carbon dioxide from exhaust gas by utilizing seawater.
The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yukishige Maezawa, Kenji SANO, Toru Ushirogouchi.
Application Number | 20130276631 13/920735 |
Document ID | / |
Family ID | 42728028 |
Filed Date | 2013-10-24 |
United States Patent
Application |
20130276631 |
Kind Code |
A1 |
SANO; Kenji ; et
al. |
October 24, 2013 |
METHOD AND SYSTEM FOR REMOVING CARBON DIOXIDE FROM EXHAUST GAS BY
UTILIZING SEAWATER
Abstract
This invention relates to a method for removing carbon dioxide
in an exhaust gas utilizing seawater, and to apparatuses for
removing carbon dioxide by the method. The method includes
producing a concentrated seawater having an increased concentration
of salt by utilizing a reverse osmosis membrane method, producing
an ammonia-saturating concentrated seawater by blowing ammonia into
the concentrated seawater, contacting a non-heated exhaust gas with
the ammonia-saturating concentrated seawater such that carbon
dioxide is absorbed in the ammonia-saturating concentrated
seawater, collecting a sediment of sodium hydrogen carbonate, and
collecting ammonium chloride from a solution comprising the
ammonium chloride produced by absorption of the carbon dioxide in
the ammonium-saturating concentrated seawater.
Inventors: |
SANO; Kenji; (Tokyo, JP)
; Maezawa; Yukishige; (Hachioji-shi, JP) ;
Ushirogouchi; Toru; (Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Family ID: |
42728028 |
Appl. No.: |
13/920735 |
Filed: |
June 18, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13208805 |
Aug 12, 2011 |
8486182 |
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13920735 |
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PCT/JP10/00866 |
Feb 12, 2010 |
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13208805 |
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Current U.S.
Class: |
95/205 ;
96/236 |
Current CPC
Class: |
B01D 53/62 20130101;
Y02C 10/06 20130101; Y02C 10/04 20130101; B01D 53/1418 20130101;
B01D 2252/102 20130101; B01D 53/1475 20130101; Y02C 20/40 20200801;
B01D 2252/1035 20130101; B01D 53/1493 20130101; B01D 2251/304
20130101; B01D 2257/504 20130101 |
Class at
Publication: |
95/205 ;
96/236 |
International
Class: |
B01D 53/14 20060101
B01D053/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 11, 2009 |
JP |
2009-058752 |
Claims
1-13. (canceled)
14. A method for removing carbon dioxide in an exhaust gas
utilizing seawater, comprising: producing a concentrated seawater
having an increased concentration of salt by utilizing a reverse
osmosis membrane method at a seawater desalination plant; producing
an ammonia-saturating concentrated seawater by blowing ammonia into
the concentrated seawater so as to be saturated; contacting a
non-heated exhaust gas with the ammonia-saturating concentrated
seawater such that carbon dioxide in the non-heated exhaust gas is
absorbed in the ammonia-saturating concentrated seawater;
collecting a sediment of sodium hydrogen carbonate produced by the
absorption of the carbon dioxide in the ammonia-saturating
concentrated seawater; and collecting an ammonium chloride from a
solution comprising the ammonium chloride produced by the
absorption of the carbon dioxide in the ammonia-saturating
concentrated seawater.
15. The method as set forth in claim 14, wherein the collecting of
an ammonium chloride is performed by spraying a solution containing
the ammonium chloride produced by the absorption of the carbon
dioxide in the ammonia-saturating concentrated seawater with a
utilization of pressure of the non-heated exhaust gas while cooling
the solution by utilizing heat of evaporation of a solvent of the
solution so as to settle out.
16. The method as set forth in claim 14, wherein the collecting of
an ammonium chloride is performed by heating the solution with a
utilization of a heated exhaust gas kept at 100.degree. C. or more
so as to chemically decompose the ammonium chloride to produce
ammonia.
17. The method as set forth in claim 16, wherein the ammonia
produced by the collecting of an ammonium chloride is the ammonia
blown into the concentrated seawater to produce the
ammonia-saturating concentrated seawater.
18. The method as set forth in claim 15, further comprising:
cooling moisture vapor produced by the spraying of the solution to
collect the moisture vapor as fresh water.
19. An apparatus for removing carbon dioxide by the method of claim
15, the apparatus comprising: a carbon dioxide absorbing tank
configured to reserve the ammonia-saturated seawater produced by
the blowing of ammonia into the concentrated seawater; a reservoir
configured to reserve the solution comprising sodium hydrogen
carbonate and ammonium chloride which are produced by the
absorption of the carbon dioxide; a first settling tank configured
to spray the solution by utilizing the pressure of the exhaust gas
and to cool the solution by utilizing heat of evaporation of the
solvent of the solution so as to settle out the sodium hydrogen
carbonate; and a second settling tank configured to spray the
solution by utilizing the pressure of the exhaust gas and to cool
the solution by utilizing the heat of evaporation of the solvent of
the solution so as to settle out the ammonium chloride.
20. An apparatus for removing carbon dioxide by the method of claim
16, the apparatus comprising: a carbon dioxide absorbing tank
configured to reserve the ammonia-saturated seawater produced by
the blowing of ammonia into the concentrated seawater; a reservoir
configured to reserve the solution comprising sodium hydrogen
carbonate and ammonium chloride which are produced by the
absorption of the carbon dioxide; an exhaust gas heating tank
configured to heat the solution with a heated exhaust gas kept at
100.degree. C. or more so as to chemically decompose the ammonium
chloride to produce ammonia; and a settling tank configured to
spray the solution by utilizing the pressure of the exhaust gas and
to cool the solution by utilizing the heat of evaporation of the
solvent of the solution so as to settle out the ammonium
chloride.
21. The system as set forth in claim 19, further comprising: a
cooling tank configured to cool moisture vapor produced by the
spraying of the solution in at least one of the first settling tank
and the second settling tank; and a second reservoir for reserving
the cooled moisture vapor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
13/208,805 filed on Aug. 12, 2011, which is a continuation of prior
International Application No. PCT/JP2010/000866, filed on Feb. 12,
2010 which is based upon and claims the benefit of priority from
Japanese Patent Application No. 2009-058752, filed on Mar. 11,
2009; the entire contents of all of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a method
and system for removing carbon dioxide from exhaust gas by
utilizing seawater.
BACKGROUND
[0003] Since thermal power plants and garbage incineration plants
have low restriction (lenient regulations) for installation site,
the thermal power plants and the garbage incineration plants are
constructed at many locations all over the world. Moreover, since a
large amount of carbon dioxide is exhausted from these plants, the
emission reduction of the carbon dioxide calls for urgent attention
in view of the recent interest to global warming issue and the
background of tightening of regulation for the global warming.
[0004] In order to reduce the amount of emission of the carbon
dioxide, the high efficiency of the plants is attempted while a
method and system for absorbing the carbon dioxide exhausted. For
example, it is taught in a conventional technique that calcium
hydroxide (Ca(OH).sub.2) and ammonia (NH.sub.3) are reacted one
another to produce ammonium hydroxide (NH.sub.4OH), which is
introduced with seawater into a predetermined treatment equipment
so that the exhaust gas containing the carbon dioxide is contacted
with the thus obtained solution containing the ammonium hydroxide
and the seawater and thus the carbon dioxide is absorbed in the
solution.
[0005] In this method, however, the calcium hydroxide is made
through the hydrolysis of calcium oxide (CaO) and the calcium oxide
is made through the thermolysis of calcium carbonate (CaCO.sub.3).
In the thermolysis of calcium carbonate, carbon dioxide is also
produced with the calcium oxide at equimolar concentration. In the
aforementioned method, therefore, when the ammonium hydroxide as
the raw material to be used for the absorption of the carbon
dioxide is produced, the carbon dioxide is also produced at
equimolar concentration so that even though the carbon dioxide in
the exhausted gas is absorbed with the ammonium hydroxide,
additional carbon dioxide is produced again at the same amount as
absorbed carbon dioxide. As a result, the problem of the reduction
of the emission amount of the carbon dioxide cannot be
realized.
[0006] Moreover, a plurality of by-products are produced at the
absorption of the carbon dioxide, but the conventional technique
does not teach the treatment for the by-products. Therefore, the
aforementioned conventional technique cannot be applied for the
absorption of the carbon dioxide exhausted from the practical
plants.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to a first embodiment.
[0008] FIG. 2 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to a second embodiment.
[0009] FIG. 3 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to a third embodiment.
[0010] FIG. 4 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to a fourth embodiment.
DETAILED DESCRIPTION
[0011] According to one embodiment, a method for removing carbon
dioxide in an exhaust gas utilizing seawater includes: blowing
ammonia into seawater to produce ammonia-saturated seawater;
contacting an exhaust gas under a state of non-heat with the
ammonia-saturated seawater so that carbon dioxide in the exhaust
gas is absorbed in the ammonia-saturated seawater; and splaying a
solution containing sodium hydrogen carbonate and ammonium chloride
which are produced through absorption of the carbon dioxide by the
ammonia-saturated seawater utilizing pressure of the exhaust gas
while cooling the solution utilizing heat of evaporation of a
solvent of the solution so as to settle out and recover the sodium
hydrogen carbonate and the ammonium chloride.
First Embodiment
[0012] FIG. 1 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to this embodiment.
[0013] As is apparent from FIG. 1, the carbon dioxide-removing
system 10 in this embodiment includes the carbon dioxide absorbing
tank 11, the first reservoir 12, the first settling tank 13 and the
second settling tank 14 which are subsequently provided from the
upstream of the removing system 10. The carbon dioxide absorbing
tank 11 is a tank for absorbing carbon dioxide in exhaust gas as
will be described hereinafter, and the first reservoir 12 is a tank
for reserving a solution of sodium hydrogen carbonate and a
solution of ammonium chloride which are produced as the result of
the absorption of the carbon dioxide at the carbon dioxide
absorbing tank 11. The first settling tank 13 and the second
settling tank 14 are tanks for settling the sodium hydrogen
carbonate and the ammonium chloride out from the solution and then
collecting the sodium hydrogen carbonate and the ammonium
chloride.
[0014] Then, the second reservoir 15 for reserving a dilute
ammonium chloride aqueous solution which is obtained from the
ammonium chloride solution by removing the ammonium chloride is
provided in the downstream of the second settling tank 14, and a
cooling tank 16 for cooling and collecting moisture vapor produced
and a third reservoir 17 for reserving fresh water which is
obtained by cooling the produced moisture vapor are provided in
parallel with the second reservoir 15.
[0015] The removal of carbon dioxide using the carbon dioxide
removing system shown in FIG. 1 is conducted below.
[0016] First of all, seawater is supplied and charged into the
carbon dioxide absorbing tank 11 via a pipe 21 while ammonia is
supplied into the carbon dioxide absorbing tank 11 from an ammonia
supplying tank 18 via a pipe 23 so that the ammonia is saturated in
the seawater to produce ammonia-saturated seawater. Then, a
non-heated exhaust gas is introduced into the carbon dioxide
absorbing tank 11 via a pipe 22 so as to be contacted with the
ammonia-saturated seawater.
[0017] In this case, the carbon dioxide contained in the exhaust
gas is chemically reacted with the ammonia-saturated seawater in
accordance with the reaction formula (1) as indicated below and
thus absorbed into the ammonia-saturated seawater. The reaction
formula (1) is the same as one of the reaction formulas related to
the production of sodium carbonate using ammonia soda process.
Here, the "non-heated exhaust gas" means an exhaust gas not
positively heated for a specific purpose and thus an exhaust gas
kept at room temperature (about 20.degree. C.), for example.
NaCl+H.sub.2O+NH.sub.3+CO.sub.2.fwdarw.NaHCO.sub.3+NH.sub.4Cl
(1)
[0018] As apparent from the reaction formula (1), when the carbon
dioxide is absorbed in the carbon dioxide absorbing tank 11, the
sodium hydrogen carbonate (baking soda) and the ammonium chloride
are produced as by-products accompanied with the absorption of the
carbon dioxide. Therefore, the step of recovering the sodium
hydrogen carbonate (baking soda) and the ammonium chloride is
required as the subsequent step.
[0019] In this embodiment, the solution containing the sodium
hydrogen carbonate and the ammonium chloride is once reserved in
the first reservoir 12 via a pipe 24 and then transferred into the
first settling tank 12 via a pipe 25 using the pressure of the
exhaust gas to be introduced into the first settling tank 13 from
the carbon dioxide absorbing tank 11 via a pipe 26.
[0020] Here, since the exhaust gas is used via the carbon dioxide
absorbing tank 11, the exhaust gas is cooled with the
ammonia-saturated seawater in the carbon dioxide absorbing tank 11
before the introduction of the exhaust gas into the carbon dioxide
absorbing tank 11 even though the exhaust gas is kept at a high
temperature.
[0021] The solubility of the ammonium chloride is higher than the
solubility of the sodium hydrogen carbonate, e.g., seven times as
high as the solubility of the sodium hydrogen carbonate at room
temperature (about 20.degree. C.). In this embodiment, therefore,
first of all, the sodium hydrogen carbonate is settled out in the
first settling tank 13 and then recovered therefrom. Concretely,
the solution containing the sodium hydrogen carbonate and the
ammonium chloride is sprayed in the first settling tank 13. In this
case, since the solvent contained in the solution is evaporated and
gasified, the solution is cooled by the heat of vaporization so
that the temperature of the solution is decreased. The solvent
mainly contains water, but may contain an additional solvent such
as non-reacted ammonia.
[0022] As a result, since the solubility of salt of the seawater in
the solution becomes equal or larger than the solubility of the
sodium hydrogen carbonate, the sodium hydrogen carbonate cannot be
dissolved anymore in the solution and thus settled out. By
recovering the thus produced sediment, therefore, the sodium
hydrogen carbonate as the by-product produced by the absorption of
the carbon dioxide can be recovered.
[0023] For example, since the content of salt of seawater is 3.5 wt
% (0.6 mol/l), if the water contained in the solution is evaporated
by means of splaying using the exhaust gas and cooled up to about
0.degree. C., the solubility of salt of seawater in the solution
can be increased almost equal to or more than the solubility of
0.77 mol/l of sodium hydrogen carbonate, so that the sodium
hydrogen carbonate can be settled out.
[0024] Then, the solution containing the residual ammonium chloride
is introduced into the second settling tank 14 from the first
settling tank 13 via a pipe 28. In this case, the solution is
splayed again in the second settling tank 14 using the pressure of
the exhaust gas. Thereby, the solubility of salt of seawater in the
solution becomes equal to or more than the solubility of the
ammonium chloride in the solution in the same manner as the sodium
hydrogen carbonate, the ammonium chloride cannot be dissolved
anymore in the solution and thus settled out. By recovering the
thus produced sediment, therefore, the ammonium chloride as the
by-product produced by the absorption of the carbon dioxide can be
recovered in the same manner as described above.
[0025] The dilute ammonium chloride aqueous solution, which is
obtained by settling the ammonium chloride out in the second
settling tank 14, is reserved in the second reservoir via a pipe
31.
[0026] Moreover, the moisture vapor produced by the splaying in the
first settling tank 13 and the second settling tank 14 is passed
through the cooling tank 16 to be made fresh water, which is
reserved in the third reservoir 17.
[0027] The exhaust gas from which the carbon dioxide is removed is
discharged from the cooling tank 16 via a pipe 32.
[0028] In this way, in this embodiment, since the carbon dioxide is
absorbed using the ammonia-saturated seawater made of seawater and
ammonia and not using a raw material to secondarily produce a large
amount of carbon dioxide, the absorption and recovery of the carbon
dioxide can be realized under the condition that additional carbon
dioxide is not produced at the same molar concentration as the
absorbed carbon dioxide. Moreover, since the sodium hydrogen
carbonate and the ammonium chloride as the by-products can be
recovered, a practical method and system can be provided for the
absorption of the carbon dioxide discharged from plants such as
thermal power plants and garbage incineration plants.
[0029] In the practical absorption of 1 g (0.023 mol) of carbon
dioxide, the equimolar ammonia is required. In this case, the
euimolar ammonia corresponds to 0.39 g of ammonia. The amount of
carbon dioxide produced in the production of 1 g of ammonia is 0.36
g according to the primary unit of data of easy-LCA (produced by
Toshiba Corp. at 2000) so that in the case of the production of
0.39 g of ammonia, 0.14 g of carbon dioxide is produced. Supposed
that carbon dioxide produced in another process is not considered,
the minimum amount of the thus produced carbon dioxide can be
estimated as 1.14 g and if 1 g of the estimated amount of the
produced carbon dioxide is absorbed and immobilized at a yield of
100%, the ratio of immobilization of the produced carbon dioxide
becomes 87.9% . Since the ratio of immobilization of the produced
carbon dioxide is not changed at a large scale, the ratio of
recover (ratio of immobilization) of the produced carbon dioxide
becomes about 88% in this embodiment.
[0030] Since the sodium hydrogen carbonate can be used as baking
soda and the ammonium chloride can be used as fertilizer, the
reaction products produced in the absorption of the carbon dioxide
can be reused not as substances harmful for human being but as
resources. In this embodiment, moreover, the seawater can be
partially made fresh water in the absorption of the carbon dioxide
as described above.
[0031] It is apparent, therefore, that the method and system for
removing the carbon dioxide in this embodiment are excellent so as
not to cause environmental destruction and the like.
[0032] In this embodiment, the exhaust gas discharged from the
cooling tank 16 may be circulated in the system shown in FIG. 1 and
treated repeatedly depending on the concentration of the carbon
dioxide of the exhaust gas. When the splaying is conducted in the
first settling tank 13 and the second settling tank 14, moreover,
another exhaust gas kept at high temperature may be introduced into
the first settling tank 13 and the second settling tank 14 via
another route so as to promote the evaporation of the solvent, that
is, the water or the like.
Second Embodiment
[0033] FIG. 2 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to this embodiment.
[0034] As is apparent from FIG. 2, the carbon dioxide-removing
system 40 in this embodiment includes a seawater-concentrating tank
41, a first reservoir 42, a carbon dioxide absorbing tank 43 and a
settling tank 44 which are subsequently provided from the upstream
of the removing system 40. As described below, the seawater
concentrating tank 41 is a tank for increasing the concentration of
salt of seawater at the carbon dioxide absorbing tank 43 so that
the absorption of carbon dioxide and the settling of sodium
hydrogen carbonate as a reaction product can be conducted
simultaneously, and the first reservoir 42 is a tank for reserving
the seawater concentrated at the seawater concentrating tank
41.
[0035] Moreover, the carbon dioxide absorbing tank 43 is a tank for
conducting the absorption of carbon dioxide and the settling of
sodium hydrogen carbonate as a reaction product simultaneously as
described above, and the settling tank 44 is a tank for settling
and recovering ammonium chloride as a reaction product.
[0036] Then, a second reservoir 45 for reserving a dilute ammonium
chloride aqueous solution which is obtained from a solution
containing the ammonium chloride by removing the ammonium chloride
is provided in the downstream of the settling tank 44. Moreover, a
cooling tank 46 for cooling the moisture vapor obtained from the
seawater through concentration and then converting the moisture
vapor into fresh water and a third reservoir 47 for reserving the
fresh water are provided in the downstream of the seawater
concentrating tank 41.
[0037] The removal of carbon dioxide using the carbon dioxide
removing system 40 shown in FIG. 2 is conducted below.
[0038] First of all, seawater is supplied and charged into the
seawater concentrating tank 11 via a pipe 51 while an exhaust gas
kept at 100.degree. C. or more is supplied into the seawater
concentrating tank 11 via a pipe 52. As the high temperature
exhaust gas can be used an exhaust gas discharged from a thermal
power plant or a garbage incineration plant as it is. In this case,
in the seawater concentrating tank 41, the moisture of the seawater
is evaporated by the exhaust gas so as to increase the
concentration of salt of the seawater within a range of 3.5 wt %
(0.6 mol/l) to 25 wt % (4.3 mol/l), for example. Here, since the
saturated concentration of salt is 30 wt % or less, it is difficult
to increase the concentration of salt of the seawater beyond 30 wt
%.
[0039] The upper limited temperature of the exhaust gas is not
particularly restricted only if the exhaust gas does not affect the
system shown in FIG. 2, particularly to the seawater concentrating
tank 41. As of now, the upper limited temperature of the exhaust
gas may be set to about 200.degree. C.
[0040] Thereafter, the thus obtained concentrated seawater is
reserved in the first reservoir 42 via a pipe 53 and then
introduced into the carbon dioxide absorbing tank 43 via a pipe 54.
On the other hand, ammonia is supplied into the carbon dioxide
absorbing tank 43 from an ammonia supplying tank 48 via a pipe 57
so as to saturate the concentrated seawater therewith and thus
produce ammonia-saturating concentrated seawater. Then, the exhaust
gas cooled at the seawater concentrating tank 41 is introduced into
the carbon dioxide absorbing tank 43 and contacted with the
ammonia-saturated seawater.
[0041] In this case, the carbon dioxide contained in the exhaust
gas is chemically reacted with the ammonia-saturating concentrated
seawater according to the aforementioned reaction formula (1) and
thus absorbed through the chemical reaction indicated in the
reaction formula (1). Simultaneously, the sodium hydrogen carbonate
(baking soda) as a reaction product cannot be dissolved in the
ammonia-saturating concentrated seawater because the concentration
of salt of the ammonia-saturating concentrated seawater is already
increased to about 25 wt % (4.3 mol/l), and thus settled out under
no splaying, different from the first embodiment.
[0042] On the other hand, since the ammonium chloride as a reaction
product similar to the sodium hydrogen carbonate has a solubility
seven times as high as the solubility of the sodium hydrogen
carbonate, the ammonium chloride cannot be settled out in the
carbon dioxide absorbing tank 43.
[0043] Therefore, the solution containing the ammonium chloride is
introduced into the settling tank 44 via a pipe 58. In this case,
the solution is splayed using the pressure of the exhaust gas in
the settling tank 44. Thereby, since the solvent, that is, the
water of the solution is evaporated while the solvent is cooled by
the heat of evaporation, the solubility of salt of the seawater in
the solution becomes equal or larger than the solubility of the
ammonium chloride in the solution. As a result, since the ammonium
chloride is settled out, the ammonia chloride can be recovered by
recovering the sediment of ammonia chloride.
[0044] The dilute ammonium chloride aqueous solution, which is
obtained by settling the ammonium chloride out in the settling tank
44, is reserved in the second reservoir 45 via a pipe 59.
[0045] Moreover, the moisture vapor produced by the introduction of
the high temperature exhaust gas is passed through the cooling tank
46 to be made fresh water, which is reserved in the third reservoir
47.
[0046] The exhaust gas from which the carbon dioxide is removed is
discharged from the carbon dioxide absorbing tank 43 via a pipe
61.
[0047] In this way, in this embodiment, since the carbon dioxide is
absorbed using the ammonia-saturating concentrated seawater made of
seawater and ammonia and not using a raw material to secondarily
produce a large amount of carbon dioxide, the absorption and
recovery of the carbon dioxide can be realized under the condition
that additional carbon dioxide is not produced at the same molar
concentration as the absorbed carbon dioxide. Moreover, since the
sodium hydrogen carbonate and the ammonium chloride as the
by-products can be recovered, a practical method and system can be
provided for the absorption of the carbon dioxide discharged from
plants such as thermal power plants and garbage incineration
plants.
[0048] Other features and advantages are similar to those in first
embodiment. For example, another cooling tank for cooling the
moisture vapor produced in the settling tank 44 may be provided and
a fourth reservoir for the cooled moisture vapor (condensed fresh
water) may be provided.
Third Embodiment
[0049] FIG. 3 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to this embodiment. This embodiment is a modified
embodiment for the first embodiment related to FIG. 1. Concretely,
the system structure in this embodiment is different from the
system structure in the first embodiment in that the second
settling tank 14 in FIG. 1 is substituted with an exhaust gas
heating tank 71 and the pipe 16 to be connected with the cooling
tank 16 is substituted with a pipe 72 to be connected with the
ammonia supplying tank 18 above the exhaust gas heating tank 71.
Therefore, only these different components will be described
below.
[0050] The absorption of carbon dioxide in the carbon dioxide
absorbing tank 11 and the settling and recovering of sodium
hydrogen carbonate as a reaction product in the first settling tank
13 are conducted in the same manner as in the first embodiment.
[0051] Then, the solution containing the residual ammonium chloride
is introduced into the exhaust gas heating tank 71 from the first
settling tank 13 via a pipe 28. In this case, another exhaust gas
kept at 100.degree. C. or more is contacted with the exhaust gas
heating tank 71 via a pipe not shown. The exhaust gas may be
splayed directly for the exhaust gas heating tank 71, but only the
thermal energy is extracted from the exhaust gas by a heat
exchanger not shown so as to heat the exhaust gas heating tank 71.
The upper limited temperature of the exhaust gas may be set in the
same manner as in the second embodiment.
[0052] In this case, the ammonium chloride in the exhaust gas
heating tank 71 is thermally decomposed according to the reaction
formula (2) to produce ammonia. If the ammonia produced in the
exhaust gas heating tank 71 is supplied into the ammonia supplying
tank 18 via the pipe 72, therefore, the ammonia as the reaction
product to be inherently treated as a salvaged material can be
reused directly for the recovering system in this embodiment as
shown in FIG. 3. Namely, the ammonium chloride can be directly and
efficiently utilized.
NH.sub.4Cl.fwdarw.NH.sub.3+HCl (2)
[0053] The thus produced hydrochloric acid (HCl) is taken out from
the exhaust gas heating tank 71 to the outside thereof via a pipe
31.
[0054] Other features and advantages are similar to those in first
embodiment.
[0055] For example, the settling tank 44 in the second embodiment
related to FIG. 2 may be substituted with the exhaust gas heating
tank 71. In this case, the function/effect of the exhaust gas
heating tank 71 is similar to the one as described above. This
embodiment including the exhaust gas heating tank 71 may be also a
modified embodiment for the second embodiment.
Fourth Embodiment
[0056] FIG. 4 is a schematic view showing the structure of a system
for removing carbon dioxide from an exhaust gas utilizing seawater
according to this embodiment. This embodiment is a modified
embodiment for the second embodiment related to FIG. 2.
[0057] Concretely, the system structure in this embodiment is
different from the system structure in the second embodiment in
that the seawater concentrating tank 41 in FIG. 2 is substituted
with a seawater desalination plant 81 utilizing reverse osmosis
membrane method. Since no moisture is produced prior to the
absorption of carbon dioxide accompanied with the provision of the
seawater desalination plant 81, the cooling tank 16 and the third
reservoir 17 are provided in parallel with the second reservoir 45
for reserving the dilute ammonium chloride aqueous solution
produced by removing the ammonium chloride from the solution
containing the ammonium chloride as a reaction product in the same
manner as in the first embodiment, instead of the cooling tank 46
and the third reservoir 47.
[0058] The seawater desalination plant 81 utilizing the reverse
osmosis membrane method is configured such that pressure is applied
to the side of seawater of the permeation membrane of the plant 81
so as to soak fresh water out from the side opposite to the
seawater side thereof. By repeating this process, the seawater at
the seawater side of the permeation membrane is concentrated to be
converted into salt water of high concentration. In this
embodiment, therefore, the seawater at the seawater side of the
permeation membrane is taken out as concentrated seawater, which is
used instead of the concentrated seawater obtained at the seawater
concentrating tank 41 in the second embodiment. The subsequent
absorption of carbon dioxide and recovery of sodium hydrogen
carbonate and ammonium chloride are conducted in the same manner as
in the second embodiment.
[0059] Moreover, moisture vapor produced by splaying is made fresh
water and reserved using the cooling tank 16 and the third
reservoir 17 in the same manner as in the first embodiment.
[0060] Other features and advantages are similar to those in first
embodiment.
[0061] According to the third embodiment, the exhaust gas heating
tank 17 may be provided instead of the settling tank 44. In this
case, the function/effect of the exhaust gas heating tank 44 is
similar to the one as described above. Therefore, this embodiment
including the exhaust gas heating tank 71 may be also a modified
embodiment for the third embodiment.
[0062] In all of the embodiments, moreover, the moisture vapor
produced in the absorption of the carbon dioxide and the recovery
of the reaction products is cooled so as to be recovered as fresh
water. However, such a process as recovering the fresh water is not
essential in these embodiments but may be omitted.
[0063] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
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