SYSTEM AND METHOD FOR RECOVERING
CARBON DIOXIDE IN EXHAUST GAS
TECHNICAL FIELD
[0001] The present invention relates to a system for recovering carbon dioxide being discharged from a thermal power plant, a municipal waste incineration plant, a natural gas extraction site or the like, and more particularly to a system and method for recovering carbon dioxide in an exhaust gas, which can recover carbon dioxide by an alkaline solution.
BACKGROUND ART
[0002] In these years, there is an increasing significant concern in connection with a global warming issue caused by a greenhouse effect of carbon dioxide which is a combustion product from the burning of fossil fuels. According to the Kyoto Protocol to the United Nations Framework Convention on Climate Change, Japan is required to reduce the greenhouse gas emission through the years of 2008-2012 to a level 6% below the total emission in 1990.
[0003] Under the circumstances as described above, there is disclosed in, for example, JP-A 4-346816 (KOKAI) a system for recovering carbon dioxide by using, for example, a potassium carbonate solution which is an alkali material as an liquid absorbent for carbon dioxide being discharged from thermal power stations, municipal waste incineration plants, natural gas extraction sites and the like. There is also disclosed in, for example, JP-A 2002-126439 (KOKAI) a system for recovering carbon dioxide by using, for example, an amine solution which is an alkali material. (See Patent Document 1, Patent Document 2)
[0004] FIG. 5 shows an overview of a conventional carbon dioxide recovery system 300 for recovering carbon dioxide by using a potassium carbonate solution as an alkaline solution.
[0005] In the conventional carbon dioxide recovery system 300 shown in FIG. 5, an exhaust gas 301 discharged when a fossil fuel is burnt is guided to an absorber 303 by a gas blower 302. An alkaline solution 304 having a temperature of about 55° C. is supplied to the top of the absorber 303, and the supplied alkaline solution 304 absorbs carbon dioxide from the exhaust gas 301 by contacting to the introduced exhaust gas 301. Meanwhile, the exhaust gas 301 from which the carbon dioxide has been absorbed by the alkaline solution 304 is released into the atmosphere from the top of the absorber 303.
[0006] The alkaline solution 304 having received the carbon dioxide is guided from a lower part of the absorber
303 to a heat exchanger 306 by an extraction pump 305 and further guided to a regenerator 307.
[0007] The alkaline solution 304 guided into the regenerator 307 is heated to a temperature of about 100° C. by steam 309 of a heater 308 and then stirred. Then, the carbon dioxide is diffused from the alkaline solution 304 and regenerated into the alkaline solution 304 capable of absorbing the carbon dioxide. The regenerated alkaline solution
304 is returned to an upper part of the absorber 303 by a circulation pump 310 via the heat exchanger 306 and a cooler 311. Meanwhile, the carbon dioxide diffused from the alkaline solution 304 is guided to a separator 313 via a cooler 312, dehydrated by the separator 313 and recovered.
[0008] In the conventional carbon dioxide recovery system 300 configured as described above, a circulation line for the alkaline solution 304 is disposed between the absorber 303 and the regenerator 307, the steam 309 of a power generation boiler is used in the regenerator 307 to heat instantaneously the alkaline solution 304 up to a temperature of about 100° C. to regenerate, and there generated alkaline solution 304 is cooled instantaneously down to a temperature of about 55° C. and returned to the absorber 303.
[0009] In the above-described conventional carbon dioxide recovery system, large heat quantity from the steam 309 of the power generation boiler is used to heat an enormous flow rate of the alkaline solution 304 instantaneously up to a prescribed temperature by the regenerator 307, so that the above system has a problem that the thermal efficiency cannot be improved.
[0010] Besides, the absorber 303 and the regenerator 307 of the conventional carbon dioxide recovery system are connected through a single circulation line, so that the alkaline solution 304 which is circulated through the absorber 303 and the regenerator 307 cannot be basically circulated at a different speed. Therefore, the enormous flow rate of the alkaline solution 304 required in the carbon dioxide absorption step cannot be lowered to a smaller flow rate in a regeneration step.
[0011] And, when the recovery system which has the absorber 303 and the regenerator 307 connected through a single circulation line uses an amine solution, it is necessary to set a temperature of the alkaline solution 304 in the absorber 303 to about 50° C. and a temperature of the alkaline solution 304 in the regenerator 307 to about 120° C. Therefore, the heat exchanger must be disposed between the absorber 303 and the regenerator 307 to make troublesome adjustment of a temperature of the alkaline solution 304.
[0012] Patent Document 1: JP-A 4-346816 (KOKAI)
[0013] Patent Document 2: JP-A 2002-126439 (KOKAI)
SUMMARY OF THE INVENTION
[0014] The present invention provides a system and a method for recovering carbon dioxide contained in an exhaust gas that can regenerate an alkaline solution without using a large volume of steam of a power generation boiler and can circulate the alkaline solution to an absorption device and a regeneration device through individually independent reflux lines.
[0015] A system for recovering carbon dioxide in an exhaust gas according to the present invention, comprises an absorption device which is provided with an exhaust gas introduction port, an alkaline solution introduction port, a remaining exhaust gas discharge port and an alkaline solution discharge port and causes gas-liquid contact between an exhaust gas introduced from the exhaust gas introduction port and an alkaline solution introduced from the alkaline solution introduction port to absorb carbon dioxide contained in the exhaust gas by the alkaline solution; a regeneration device which is provided with an alkaline solution spurt port, a regenerated alkaline solution discharge port and a carbon dioxide discharge port and discharges carbon dioxide from the alkaline solution having absorbed the carbon dioxide to regenerate the alkaline solution; a first alkaline solution reflux line which refluxes the alkaline
solution being discharged from the alkaline solution discharge port of the absorption device to the alkaline solution introduction port; a second alkaline solution reflux line which refluxes the regenerated alkaline solution being discharged from the regenerated alkaline solution discharge port of the regeneration device to the alkaline solution spurt port; and a storage tank which is comprised of a plurality of split tanks capable of intervening in either the first alkaline solution reflux line or the second alkaline solution reflux line by switching the alkaline solution reflux lines.
[0016] According to the system for recovering the carbon dioxide in the exhaust gas, the first alkaline solution reflux line, which refluxes the alkaline solution being discharged from the alkaline solution discharge port of the absorption device to the alkaline solution introduction port and absorbs carbon dioxide, and the second alkaline solution reflux line, which refluxes the regenerated alkaline solution being discharged from the regenerated alkaline solution discharge port of the regeneration device to the alkaline solution spurt port and discharges carbon dioxide to regenerate the alkaline solution can be disposed separately and independently. Thus, the flow rates of the alkaline solutions flowing through the individual alkaline solution reflux lines can be set independently, and a reflux flow rate and the like of the alkaline solution suitable for each of the carbon dioxide absorption operation and the alkaline solution regeneration operation can be set. And, the system for recovering carbon dioxide contained in an exhaust gas does not need to heat instantaneously the alkaline solution by the regeneration device and does not need a large heating device or large heat quantity. Thus, the thermal efficiency of the system can be improved.
[0017] A method for recovering carbon dioxide in an exhaust gas according to the present invention, comprises a first absorption step which refluxes a first alkaline solution being discharged from an alkaline solution discharge port of an absorption device to an alkaline solution introduction port of the absorption device through a first split tank among a plurality of split tanks configuring a storage tank to cause gas-liquid contact between the exhaust gas and the first alkaline solution to repeatedly absorb carbon dioxide contained in the exhaust gas by the first alkaline solution; and a first regeneration step which switches a reflux line of the first alkaline solution to introduce the first alkaline solution having absorbed the carbon dioxide in the first absorption step to an alkaline solution spurt port of a regeneration device, refluxes the first alkaline solution being discharged from a regenerated alkaline solution discharge port of the regeneration device to the alkaline solution spurt port through the first split tank, and discharges repeatedly the carbon dioxide into the regeneration device to regenerate the carbon dioxide absorption capacity of the first alkaline solution.
[0018] According to the method for recovering carbon dioxide contained in an exhaust gas, the reflux line of the first alkaline solution which absorbs carbon dioxide and the reflux line of the alkaline solution to regenerate the first alkaline solution by discharging the carbon dioxide are separately disposed independently, and the reflux lines can be switched to selectively reflux the first alkaline solution to the individual reflux lines. The flow rates of the first alkaline solutions flowing through the individual reflux lines can be set individually, and a reflux flow rate and the like of the first
alkaline solution suitable for a carbon dioxide absorption operation and an alkaline solution regeneration operation can be set. The system for recovering carbon dioxide contained in the exhaust gas does not need to heat instantaneously the alkaline solution by the regeneration device and does not need a large heating device or large heat quantity. Thus, the thermal efficiency of the system can be improved.
[0019] The method for recovering carbon dioxide in an exhaust gas, further comprises a second absorption step which guides a second alkaline solution stored in a second split tank of the storage tank to the alkaline solution introduction port of the absorption device when the first regeneration step is being performed, refluxes the second alkaline solution being discharged from the alkaline solution discharge port of the absorption device to the alkaline solution introduction port through the second split tank and causes gas-liquid contact between the exhaust gas and the second alkaline solution to repeatedly absorb the carbon dioxide contained in the exhaust gas by the second alkaline solution.
[0020] A system for recovering carbon dioxide in an exhaust gas according to the present invention, comprises an absorption device which is provided with an exhaust gas introduction port, an alkaline solution introduction port, a remaining exhaust gas discharge port and an alkaline solution discharge port, and causes gas-liquid contact between the introduced exhaust gas and an alkaline solution to absorb carbon dioxide contained in the exhaust gas by the alkaline solution to produce a reaction product insoluble compound; an alkaline solution reflux line which refluxes the alkaline solution being discharged from the alkaline solution discharge port of the absorption device to the alkaline solution introduction port; and a collection tank which is intervened in the alkaline solution reflux line or connected by a pipe branched from the alkaline solution reflux line to collect an insoluble compound contained in the alkaline solution.
[0021] According to the system for recovering carbon dioxide contained in the exhaust gas, the reaction product insoluble compound produced as a result of the absorption of the carbon dioxide contained in the exhaust gas by the alkaline solution within the absorption device flows together with the alkaline solution through the alkaline solution reflux line to reach the collection tank. The insoluble compound has a specific gravity larger than that of the alkaline solution, so that the insoluble compound deposits on a lower part of the collection tank, and the insoluble compound deposited in the collection tank can be collected. And, the alkaline solution which is especially at an upper part of the collection tank and did not contribute to the generation of the insoluble compound can be refluxed again to the alkaline solution introduction port through the alkaline solution reflux line.
[0022] The system for recovering carbon dioxide in an exhaust gas, further comprises a regeneration device to which the insoluble compound is supplied and which heats the insoluble compound to discharge carbon dioxide to regenerate an alkali material, which configures the alkaline solution, from the insoluble compound.
[0023] A method for recovering carbon dioxide in an exhaust gas according to the present invention, comprises an absorption step which causes gas-liquid contact between the exhaust gas and an alkaline solution and absorbs the carbon dioxide contained in the exhaust gas by the alkaline solution
to generate a reaction product insoluble compound; a circulation step which causes repeatedly gas-liquid contact between the alkaline solution and the exhaust gas; and a collection step which collects the insoluble compound contained in the alkaline solution.
[0024] According to the method for recovering the carbon dioxide contained in the exhaust gas, the reaction product insoluble compound which is produced as a result of the absorption of the carbon dioxide contained in the exhaust gas by the alkaline solution in the absorption step has a specific gravity larger than that of the alkaline solution in the collection step, so that the insoluble compound deposits on a lower part of the collection tank. Thus, the deposited insoluble compound can be collected in the collection step. And, the alkaline solution which did not contribute to the generation of the insoluble compound can be subjected to the gas-liquid contact again with the exhaust gas in the circulation step.
[0025] The method for recovering carbon dioxide in an exhaust gas, further comprises a regeneration step which heats the insoluble compound collected in the collection step to discharge the carbon dioxide and regenerates an alkali material, which configures the alkaline solution, from the insoluble compound.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] [FIG. 1]FIG. 1 is a general view showing a carbon dioxide recovery system of a first embodiment of the present invention.
[0027] [FIG. 2]FIG. 2 is a general view showing a carbon dioxide recovery system of a fourth embodiment of the present invention.
[0028] [FIG. 3]FIG. 3 is a general view showing a carbon dioxide recovery system of a fifth embodiment of the present invention.
[0029] [FIG. 4]FIG. 4 is a diagram showing the results of measuring a carbon dioxide recovery rate by an alkaline solution.
[0030] [FIG. 5]FIG. 5 is a general view showing a conventional carbon dioxide recovery system.
BEST MODE FOR IMPLEMENTING THE
INVENTION
[0031] Embodiments of the present invention will be described with reference to the drawings.
FIRST EMBODIMENT
[0032] FIG. 1 shows a general view of a carbon dioxide recovery system 10 of the first embodiment of the present invention.
[0033] The carbon dioxide recovery system 10 is mainly comprised of an absorber 100 in which gas-liquid contact of the introduced exhaust gas and an alkaline solution is performed, a regenerator 110 which generates an alkaline solution by discharging carbon dioxide from the alkaline solution having absorbed the carbon dioxide, alkaline solution reflux lines 120a, 1206 which reflux the alkaline solution being discharged from an alkaline solution discharge port 101 of the absorber 100 to an alkaline solution intro
duction port 102, alkaline solution reflux lines 121a, 1216 which reflux the regenerated alkaline solution being discharged from a regenerated alkaline solution discharge port 111 of the regenerator 110 to an alkaline solution jet port 112, a storage tank 130 which is comprised of plural split tanks 130a, 1306 intervened in the alkaline solution reflux lines 120a, 1206 or the alkaline solution reflux lines 121a, 1216, and a control section 140 which controls pumps, valves and individual equipment.
[0034] In FIG. 1, the control section 140 is electrically connected to individual pumps, valves, measuring equipment and individual construction equipment, but their connection lines are omitted for convenience of clear illustration.
[0035] First, an alkaline solution reflux path for refluxing an alkaline solution 160 being discharged from the alkaline solution discharge port 101 of the absorber 100 to the alkaline solution introduction port 102 will be described.
[0036] An exhaust gas introduction port 104 for guiding an exhaust gas 103 containing carbon dioxide discharged from a thermal power plant, a municipal waste incineration plant or the like into the absorber 100 is formed at a lower part of the absorber 100. And, a gas blower 105 for blowing the exhaust gas 103 into the absorber 100 is connected to the exhaust gas introduction port 104. The alkaline solution introduction port 102 which introduces the alkaline solution 160 being supplied from the storage tank 130 by a feed pump 150 is formed at an upper part of the absorber 100. The alkaline solution introduction port 102 is provided with an alkaline solution jet part 106 for jetting the alkaline solution 160. Besides, the absorber 100 has therein a packing 107 for causing mainly gas-liquid contact of the alkaline solution 160 which is jetted from the alkaline solution jet part 106 and the exhaust gas 103 which is introduced into the absorber 100. An exhaust port 108 is disposed at the top end of the absorber 100 to exhaust the exhaust gas 103 having the carbon dioxide absorbed by passing through the packing 107 to the atmosphere.
[0037] Besides, the alkaline solution discharge port 101 for discharging the alkaline solution 160 having absorbed the carbon dioxide is disposed at the bottom of the absorber 100. The alkaline solution discharge port 101 is connected to one end of the alkaline solution reflux line 120a on which a delivery pump 151 is provided. The other end of the alkaline solution reflux line 120a is branched in correspondence with the divided split tanks 130a, 1306, and the branched ends of the alkaline solution reflux line 120a each are provided with a valve 170.
[0038] Besides, the individual split tanks 130a, 1306 each have a valve 171, and the alkaline solution reflux line 1206 which has its one end branched in correspondence with the individual split tanks 130a, 1306 is disposed. The branched ends of the alkaline solution reflux line 1206 are dipped to reach a relatively lower part in the alkaline solution stored in the individual split tanks 130a, 1306. And, the other end of the alkaline solution reflux line 1206 is connected to the alkaline solution introduction port 102 of the absorber 100. The alkaline solution reflux line 1206 is provided with the feed pump 150 for feeding under pressure the alkaline solution 160 to the absorber 100.
[0039] For example, the valve 170 and thevalve 171 corresponding to the split tank 130a are opened and the
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