CARBON DIOXIDE RECOVERY DEVICE

A carbon dioxide recovery device provided with a separation device that separates carbon dioxide from to-be-separated gas (for example, combustion exhaust gas) containing carbon dioxide, wherein: in order from the upstream side where the to-be-separated gas is supplied, the separation device and carbon dioxide sublimators, which sublimate (solidify) carbon dioxide that was separated in the separation device, are connected in series, refrigerant circuits in which a fluid having cold heat serves as the refrigerant, are connected to the carbon dioxide sublimators, and the refrigerant is used to sublimate (solidify) the carbon dioxide; and when the carbon dioxide is sublimated (solidified), the carbon dioxide sublimators are depressurized and set to negative pressure so as to draw in the carbon dioxide separated at the separation device.

TECHNICAL FIELD

The present invention relates to a carbon dioxide recovery device provided with a separation device for separating carbon dioxide from to-be-separated gas including the carbon dioxide.

BACKGROUND ART

In recent years, climate change issues have become an imminent problem, and thus there has been demanded to develop a technique of separating and recovering carbon dioxide from gas such as combustion exhaust gas including carbon dioxide so that emission of carbon dioxide into the atmosphere is avoided. Further, a demand for carbon dioxide such as carbon dioxide gas used for welding and dry ice for distribution has been increasing. Under a circumstance of delay in supply in response to this increasing demand, there is a tendency of yearly increase in an import amount of carbon dioxide in our country. However, when carbon dioxide is to be imported in a form of dry ice, a part of it could melt during transportation, resulting in huge loss in the amount. In this situation, there has been a demand for a device that can recover or capture carbon dioxide with high purity by utilizing carbon dioxide included in combustion exhaust gas and the like emitted in a power plant.

As a device for recovering carbon dioxide with high purity from the exhaust gas and the like, there has been known a carbon dioxide recovery device including an absorption tower to absorb carbon dioxide in an absorption liquid and a regeneration tower to diffuse carbon dioxide with vapor from the absorption liquid that has absorbed carbon dioxide as disclosed in the Patent Document 1.

In the regeneration tower, the absorption liquid that has absorbed carbon dioxide is heated to a boiling temperature to perform diffusion of carbon dioxide and vapor. In order to suppress an amount of energy consumption for this heating, in the Patent Document 1, the regeneration tower is depressurized to lower the boiling temperature of the absorption liquid having absorbed the carbon dioxide for energy saving.

RELATED ART DOCUMENTS

Patent Documents

SUMMARY OF INVENTION

Problems to be Solved by the Invention

However, the above conventional technique has the following problem.

The carbon dioxide recovery device disclosed in the Patent Document 1 uses a vacuum pump for depressurizing the regeneration tower. Operation of this vacuum pump requires a large amount of electric power, and thus there is a concern about increase in electric power cost and generation of further carbon dioxide for power generation. To address this, there has been a demand for a carbon dioxide recovery device which can achieve further energy saving in order to suppress increase in the electric power cost and generation of further carbon dioxide for power generation.

The present invention has been made to provide a carbon dioxide recovery device that can recover carbon dioxide while achieving further energy saving.

Means of Solving the Problems

To achieve the above purpose, a carbon dioxide recovery device according to one aspect of the present invention has the following configuration.

The carbon dioxide recovery device has the feature that the device comprising a separation device to separate carbon dioxide from to-be-separated gas including the carbon dioxide, wherein the separation device and a carbon dioxide sublimator to sublimate (solidify) the carbon dioxide having been separated by the separation device are connected in series in order from an upstream side of supplying the to-be-separated gas, the carbon dioxide sublimator is connected with a refrigerant circuit in which a fluid having cold heat is utilized as a refrigerant, and the carbon dioxide is sublimated (solidified) by the refrigerant, and when the carbon dioxide is sublimated (solidified), the carbon dioxide sublimator is depressurized to be under negative pressure so that the carbon dioxide having been separated by the separation device is sucked.

According to the above-mentioned carbon dioxide recovery device, the separation device of separating the carbon dioxide from the to-be-separated gas and emitting the separated carbon dioxide and the carbon dioxide sublimator of sublimating (solidifying) the carbon dioxide are connected in series. The carbon dioxide separated by the separation device is emitted from the separation device and then flows to the carbon dioxide sublimator. The carbon dioxide having reached the carbon dioxide sublimator is cooled down by the refrigerant, which utilizes the fluid having the cold heat, and is then sublimated (solidified). Dry ice generated by this sublimation (solidification) of the carbon dioxide is recovered by sublimation (gasification) again, and thus the carbon dioxide can be utilized as carbon dioxide gas or the like.

When the carbon dioxide is to be sublimated (solidified), the carbon dioxide sublimator is depressurized to be under the negative pressure. The carbon dioxide emitted from the separation device is sucked by this negative pressure. This suction causes flow of the carbon dioxide from the separation device to the carbon dioxide sublimator, so that sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimator is promoted. Suction of the carbon dioxide is performed by utilizing the fluid having the cold heat, and thus a pump or the like for suction is not necessary and energy conservation can be achieved. This energy conservation further achieves suppression in the increase in electric power cost and achieves suppression in the generation of further carbon dioxide for power generation.

As the fluid having the cold heat, there are provided for example, liquefied fuel and liquefied gas. The liquefied fuel is, for example, liquefied natural gas (LNG), liquid hydrogen, liquefied methane, and others. Natural gas as main material for city gas is imported in a form of LNG and then re-gasified in an LNG terminal and shipped by a gas pipeline. In regasification of the LNG, a large amount of cold heat energy is released, and this cold heat energy has attracted attention as unused energy. Accordingly, as mentioned above, utilizing the cold heat of the liquefied fuel for suction of the carbon dioxide results in good use of unused energy, so that a carbon dioxide recovery device can be made ecological. Herein, as the liquefied fuel, liquid hydrogen can be given other than the LNG. Further, the liquefied gas is, for example, exemplified as liquid nitrogen and liquid oxygen. Furthermore, the fluid having the cold heat is not necessarily in a form of liquid but may be gas, slurry, and gas-liquid multiphase flow.

Effects of the Invention

The carbon dioxide recovery device according to the present invention has the above-mentioned configuration, and thus can achieve recovery of carbon dioxide while saving energy.

MODE FOR CARRYING OUT THE INVENTION

First Embodiment

Firstly, a first embodiment of a carbon dioxide recovery device of the present invention is explained in detail with reference to the accompanying drawings.

FIG.1is a schematic view showing a configuration of a carbon dioxide recovery device1A according to the first embodiment. The carbon dioxide recovery device1A is provided with, as shown inFIG.1, a separation device60, water vapor condensers4A,4B, and carbon dioxide sublimators5A,5B.

The separation device60is configured with an absorption tower2and a regeneration tower3. The absorption tower2is, for example, a countercurrent gas-liquid contact device and is filled inside with a filler21such as Raschig ring.

Further, the absorption tower2is provided with a gas introduction port22below the filler21, and to the gas introduction port22, a gas supply passage L11is connected. Combustion exhaust gas (one example of to-be-separated gas), which is for example generated in a power plant, an iron manufacturing plant, and a cement plant, is supplied from the gas supply passage L11to the absorption tower2. As the to-be-separated gas, the gas is not limited to the combustion exhaust gas but may be in the atmosphere. Other than that, biogas may be used, and off-gas including carbon dioxide generated from a heat treatment furnace such as a carburizing furnace and a chemical reaction device may be used.

The combustion exhaust gas includes carbon dioxide in its about 10 to 20% and also includes nitrogen, oxygen, and others. The combustion exhaust gas is considered to include sulfur oxide, and thus a desulfurization unit may be provided on the gas supply passage L11so that the combustion exhaust gas that has been removed with the sulfur oxide is supplied to the absorption tower2.

The absorption tower2is further provided with an absorption liquid introduction port23above the filler21to introduce the absorption liquid (lean liquid). As the absorption liquid, amino-based solvents and physical absorption liquid may be adapted. There are raised examples of amine as Monoethanolamine (MEA), Diethanolamine (DEA), Triethanolamine (TEA), Diethylethanolamine (DEEA), Diisopropylamine (DIPA), Aminoethoxyethanol (AEE), and Methyl diethanolamine (MDEA). There are raised examples of the physical absorption liquid as a derivative of chemical compound and Cycloetramethylene Sulfone (Sulfolane), aliphatic acid amide, NMP (N-Methyl-2-pyrrolidone), N-Alkylated 2-Pyrrolidone and corresponding Piperidone, and dialkyl-ether-group mixture of methanol and polyethylene glycol.

However, the most preferable one of the absorption liquid is amine solvent in which 2-(Ethylamino) ethanol and Diethylene Glycol Monoethyl Ether are mixed to have amine concentration of about 30% (hereinafter, referred as amine solvent according to the present embodiment). Application of the amine solvent according to the present embodiment achieves further efficient regeneration of the absorbed carbon dioxide as compared with conventionally known amine solvent (MEA solvent mixed to have about 30% of the amine concentration, which is hereinafter referred as a conventional solvent).

FIG.11is a graph showing a solubility of carbon dioxide in the amine solvent according to the present embodiment, andFIG.12is a graph showing the solubility of the carbon dioxide according to the conventional liquid. Both graphs ofFIGS.11and12illustrate the solubility under the atmosphere of 40 degrees centigrade.

For example, when a pressure at the time of absorbing the carbon dioxide is set as 10 kPa and the pressure at the time of regenerating the absorbed carbon dioxide is set as 1 kPa, as shown inFIG.11andFIG.12, the amine solvent according to the present embodiment has a solubility gap D11of carbon dioxide between the time of absorbing and the time of regenerating as about 0.25 (mol-CO2/mol-amine), and the conventional solvent has a solubility gap D12between absorbing and regenerating as about 0.08 (mol-CO2/mol-amine). The bigger this solubility gap becomes, the more a regeneration amount of carbon dioxide becomes. The amine solvent according to the present embodiment has the solubility gap D11about three times as large as the solubility gap D12of the conventional solvent, and thus the amine solvent according to the present embodiment can perform regeneration of the absorbed carbon dioxide more efficiently than the conventional solvent.

The combustion exhaust gas supplied from the gas introduction port22to the absorption tower2ascends inside the absorption tower2, and absorption liquid (lean liquid) introduced from the absorption liquid introduction port23to the absorption tower2falls down toward the filler21. Further, the combustion exhaust gas supplied to the absorption tower2also goes up toward the filler21. Thus, the absorption liquid (the lean liquid) is brought into a gas-liquid contact with the combustion exhaust gas while the liquid is falling down along a surface of the filler21, so that the liquid selectively absorbs carbon dioxide in the combustion exhaust gas. The combustion exhaust gas (nitrogen and oxygen) that has been removed with carbon dioxide is discharged through a discharge passage L12which is connected to a top portion of the absorption tower2, and the absorption liquid (the lean liquid) which has absorbed the carbon dioxide is discharged from a discharge port24on a bottom part of the absorption tower2.

The discharge port24of the absorption tower2is connected with one end of a take-out pipe L13, and the other end of the take-out pipe L13is connected to the regeneration tower3. The absorption liquid (the lean liquid) discharged to the take-out pipe L13from the absorption tower2passes through a heat exchanger6and then is transferred to the regeneration tower3.

The regeneration tower3is for example a countercurrent gas-liquid contact device and is filled inside with a filler31such as Raschig ring.

The regeneration tower3is provided with an absorption liquid introduction port32connected with the take-out pipe L13above the filler31, and the absorption liquid (rich liquid) transferred from the absorption liquid introduction port32through the take-out pipe L13is supplied. The absorption liquid (the rich liquid) supplied from the absorption liquid introduction port32falls down to the filler31.

The absorption liquid (the rich liquid) is heated to reach a boiling temperature while the liquid is falling down in the regeneration tower, so that the liquid diffuses carbon dioxide with water vapor. Heating of the absorption liquid (the rich liquid) is, for example, performed by a heat pump7utilizing waste heat and ambient heat or a heat pump8utilizing heat generated when the absorption liquid (the lean liquid) absorbs carbon dioxide in the absorption tower2. Inside the regeneration tower3is depressurized to about 4 kPa (which will be explained in detail later), for example, and thus the boiling temperature is lowered (the boiling temperature of water is about 29 degrees under a circumstance of about 4 kPa). Accordingly, energy consumption for heating the absorption liquid (the rich liquid) can be suppressed.

The absorption liquid (the lean liquid) that has diffused the carbon dioxide is discharged from a discharge port33on a bottom part of the regeneration tower3. The absorption liquid (the lean liquid) that has been discharged to a take-out pipe L14from the regeneration tower3passes through the heat exchanger6and is then returned to the absorption tower2. The take-out pipe L14is connected with the absorption liquid introduction port23of the absorption tower2, and thus the absorption liquid (the lean liquid) that has been returned to the absorption tower2falls down to the filler21to be reused for absorbing the carbon dioxide.

Further, the carbon dioxide and the water vapor which have been diffused are discharged to a first transfer pipe L15from a top portion of the regeneration tower3. This discharge operation is performed by sucking the carbon dioxide and the water vapor by use of negative pressure generated in the carbon dioxide sublimators5A,5B (the negative pressure generated in the carbon dioxide sublimators5A,5B will be explained later).

The first transfer pipe L15is branched into a branch transfer pipe L151A and a branch transfer pipe L151B by a switching valve11. Through this branching, a carbon dioxide recovery line10A configured with a water vapor condenser4A and the carbon dioxide sublimator5A which are connected in series and a carbon dioxide recovery line10B configured with a water vapor condenser4B and the carbon dioxide sublimator5B which are connected in series are connected in parallel to the regeneration tower3. Then, operation of the switching valve11allows selection of flow of the carbon dioxide and the water vapor which are discharged from the regeneration tower3to either one of the carbon dioxide recovery lines10A and10B.

A configuration of the carbon dioxide recovery line10A (10B) is explained in detail. The regeneration tower3is connected to the water vapor condenser4A (4B) via the first transfer pipe L15and the branch transfer pipe L151A (L151B). Herein, the branch transfer pipe L151A (L151B) is provided with an open-close valve13A (13B) between the switching valve11and the water vapor condenser4A (4B).

The water vapor condenser4A (4B) is provided inside with a heat exchanger41A (41B). The heat exchanger41A is used for cooling the water vapor and the carbon dioxide inside the condenser by a refrigerant flowing through a refrigerant circuit12A (12B) which will be explained later. The water vapor condenser4A (4B) is further connected with a heat pump42A (42B) utilizing waste heat and ambient heat and a drain43A (43B). The drain43A (43B) is provided with an open-close valve15A (15B).

Further, the water vapor condenser4A (4B) is connected to the carbon dioxide sublimator5A (5B) via a second transfer pipe L16A (L16B). Herein, the second transfer pipe L16A (L16B) is provided with an open-close valve14A (14B) between the water vapor condenser4A (4B) and the carbon dioxide sublimator5A (5B).

The carbon dioxide sublimator5A (5B) is provided with a heat exchanger51A (51B) inside. The heat exchanger51A (51B) is used for cooling the carbon dioxide in the sublimator by the refrigerant flowing through the refrigerant circuit12A (12B) which will be explained later. The carbon dioxide sublimator5A (5B) is further connected with a heat pump52A (52B) utilizing the waste heat and the ambient heat, a drain53A (53B), and a take-out pipe54A (54B). The drain53A (53B) is provided with an open-close valve16A (16B), and the take-out pipe54A includes an open-close valve17A (17B).

Further, the carbon dioxide recovery lines10A,10B are configured with the refrigerant circuits12A,12B, respectively so that the refrigerant flows in an order of the carbon dioxide sublimators5A,5B, and the water vapor condensers4A,4B. Moreover, the refrigerant circuits12A,12B are integrated after passing the water vapor condensers4A,4B so that the refrigerant having flown through the water vapor condensers4A,4B further flows into the absorption tower2. As the refrigerant, cold heat after regasification of liquefied fuel (one example of a fluid) is used. The liquefied fuel is, for example, liquefied natural gas, liquid hydrogen, liquefied methane, and others. For example, the cold heat after regasification of the liquefied gas may be used as the refrigerant. The liquefied gas is, for example, exemplified as liquid nitrogen, liquid oxygen, and others.

The function of the refrigerant, the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) in the above-configured carbon dioxide recovery device1is explained below.

The refrigerant passes through the refrigerant circuit12A (12B) to firstly be cooled inside the carbon dioxide sublimator5A (5B) by the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B). When liquefied natural gas is used as the liquefied fuel, the cold heat is minus 162 degrees centigrade, and when liquid hydrogen is used, the cold heat is minus 253 degrees centigrade. The temperature inside the carbon dioxide sublimator5A (5B) is however cooled to a temperature appropriate for sublimation (solidification) of the carbon dioxide by controlling a temperature gap by the heat exchanger51A (51B) or by utilizing a separate operation medium or a refrigerant. For example, when combustion exhaust gas from an iron manufacturing plant or a cement plant is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 85 degrees centigrade or below. Further, when the combustion exhaust gas from a power plant is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 96 degrees centigrade or below. Furthermore, when the atmosphere is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 140 degrees centigrade or below.

The temperature appropriate for sublimation (solidification) of the carbon dioxide inside the carbon dioxide sublimator5A (5B) varies depending on a type of the to-be-separated gas because a partial pressure of the carbon dioxide in the to-be-separated gas is different according to the type of the to-be-separated gas. Herein,FIG.15is a graph showing a range of partial pressure values of carbon dioxide in the combustion exhaust gas (represented as a first combustion exhaust gas inFIG.15) from the iron manufacturing plant or the cement plant, the combustion exhaust gas (represented as a second combustion exhaust gas inFIG.15) from the power plant, and in the atmosphere.

For example, the maximum partial pressure P11of the carbon dioxide in the combustion exhaust gas from the iron manufacturing plant or the cement plant is about 60 kPa. Then, the temperature corresponding to this partial pressure P11at which the carbon dioxide is in a gas-solid balanced state is about minus 85 degrees centigrade. Therefore, when the combustion exhaust gas from the iron manufacturing plant or the cement plant is used as the to-be-separated gas, in order to sublimate (solidify) the carbon dioxide, it is preferable to cool it inside the carbon dioxide sublimator5A (5B) to the temperature of about minus 85 degrees centigrade or below.

Further for example, the maximum partial pressure P12of the carbon dioxide in the combustion exhaust gas from the power plant is about 21 kPa. Then, the temperature corresponding to this partial pressure P12at which the carbon dioxide is in the gas-solid balanced state is about minus 96 degrees centigrade. Accordingly, when the combustion exhaust gas from the power plant is used as the to-be-separated gas, in order to sublimate (solidify) the carbon dioxide, it is preferable to cool it inside the carbon dioxide sublimator5A (5B) to the temperature of about minus 96 degrees centigrade or below.

Further for example, the maximum partial pressure P13of the carbon dioxide in the atmosphere is about 0.045 kPa. Then, the temperature corresponding to this partial pressure P13at which the carbon dioxide is in the gas-solid balanced state is about minus 140 degrees centigrade. Accordingly, when the atmosphere is used as the to-be-separated gas, in order to sublimate (solidify) the carbon dioxide, it is preferable to cool it inside the carbon dioxide sublimator5A (5B) to the temperature of about minus 140 degrees centigrade or below.

Cooling down the temperature inside the carbon dioxide sublimator5A (5B) to the temperature appropriate for sublimation (solidification) of the carbon dioxide causes sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimator5A (5B) to form dry ice. The MEA solvent that has remained in sublimation (solidification) is discharged from the drain53A (53B) by opening the open-close valve16A (16B). Further, when the carbon dioxide that has turned dry ice is to be recovered, the open-close valve17A (17B) is opened to bring the carbon dioxide sublimator5A (5B) back to the normal temperature so that the dry ice is sublimated (gasified) and recovered from the take-out pipe54A (54B). At this time, the open-close valves14A (14B),16A (16B) are in a valve-closed state so that the sublimated (gasified) carbon dioxide would not flow in any parts other than the take-out pipe54A (54B). Then, the thus recovered carbon dioxide is utilized as carbon dioxide gas or the like.

When the carbon dioxide is to be recovered, sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B needs to be interrupted. However, as mentioned above, it is selectable to make frow the carbon dioxide and the water vapor that are discharged from the regeneration tower3into either one of the carbon dioxide recovery lines10A,10B. Accordingly, while the carbon dioxide is recovered from the carbon dioxide sublimator5A of the one carbon dioxide recovery line10A, the carbon dioxide sublimator5B of the other carbon dioxide recovery line10B can continuously sublimate (solidify) the carbon dioxide. Thus, the carbon dioxide can be further efficiently recovered.

When sublimation (solidification) of the carbon dioxide is performed in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to be under negative pressure. Thereby, the carbon dioxide sublimator5A (5B) functions as a pump to perform suction of the water vapor and the carbon dioxide that have been diffused in the regeneration tower3. This suction creates flow of the water vapor and the carbon dioxide toward the carbon dioxide recovery line10A (10B).

Further, in accordance with depressurizing of the carbon dioxide sublimator5A (5B), the regeneration tower3connected in series is also depressurized, so that a boiling temperature of the absorption liquid in the regeneration tower3is lowered. Accordingly, consumption energy for heating the absorption liquid can be suppressed. In the present embodiment, the regeneration tower3is depressurized to about 4 kPa as mentioned above. The pressure of the regeneration tower3is adjusted by a decompression valve9provided on the first transfer pipe L15.

After cooling inside the carbon dioxide sublimator5A (5B), the refrigerant subsequently is cooled inside the water vapor condenser4A (4B) by the heat exchanger41A (41B) provided in the water vapor condenser4A (4B). The refrigerant has been raised its temperature by heat exchanging in the heat exchanger51A (51B), so that the refrigerant is cooled to about 1 degree centigrade.

Since the water vapor condenser4A (4B) is about 1 degree centigrade, the carbon dioxide and the water vapor which are sucked by the negative pressure generated in the carbon dioxide sublimator5A (5B) and thus discharged from the regeneration tower3are made to flow into the water vapor condenser4A (4B) to be cooled down to about 20 degrees centigrade. Thereby, the water vapor is condensed to become water. The water is stored on a bottom part of the water vapor condenser4A (4B), and the thus stored water is discharged through the drain43A (43B) by opening the open-close valve15A (15B). Herein, the drain43A (43B) may be connected to the regeneration tower3to reuse the water in the regeneration tower3.

The carbon dioxide that has flown with the water vapor in the water vapor condenser4A (4B) remains as gaseous body in a temperature of about 20 degrees centigrade, and accordingly, the carbon dioxide is sucked by the carbon dioxide sublimator5A (5B) so that the carbon dioxide passes through the second transfer pipe L16A (L16B) and flows in the carbon dioxide sublimator5A (5B). Then, the carbon dioxide having flown into the carbon dioxide sublimator5A (B) is sublimated (solidified) to become dry ice as mentioned above.

Subsequently, the refrigerant is used for cooling the absorption tower2after cooling inside the water vapor condenser4A (4B). An object of cooling the absorption tower2is to restrain temperature increase in the absorption tower2due to heat generation that is caused when the absorption liquid absorbs the carbon dioxide.

As mentioned above, the carbon dioxide recovery device1A according to the first embodiment comprises the separation device60to separate carbon dioxide from the to-be-separated gas including the carbon dioxide, wherein the separation device60and the carbon dioxide sublimators5A,5B to sublimate (solidify) the carbon dioxide, which has been separated by the separation device, are connected in series in order from an upstream side of supplying the to-be-separated gas. The carbon dioxide sublimators5A,5B are connected with the refrigerant circuits12A,12B in which a fluid having the cold heat is utilized as the refrigerant, and the carbon dioxide is sublimated (solidified) by the refrigerant, and when the carbon dioxide is sublimated (solidified), the carbon dioxide sublimators5A,5B are depressurized to be under negative pressure so that the carbon dioxide that has been separated by the separation device60is sucked.

According to the above-mentioned carbon dioxide recovery device1A, the separation device60for separating the carbon dioxide from the to-be-separated gas and emitting the separated carbon dioxide and the carbon dioxide sublimators5A,5B for sublimating (solidifying) the carbon dioxide are connected in series. The carbon dioxide separated by the separation device60is emitted from the separation device60and then flows to the carbon dioxide sublimators5A,5B. The carbon dioxide having reached the carbon dioxide sublimators5A,5B is cooled down by the refrigerant, which utilizes the fluid having the cold heat, and then sublimated (solidified). Dry ice generated by this sublimation (solidification) of the carbon dioxide is recovered by sublimating (solidification) again, and thus the carbon dioxide can be utilized as carbon dioxide gas or the like.

When the carbon dioxide is to be sublimated (solidified), the carbon dioxide sublimators5A,5B are depressurized to be under the negative pressure. The carbon dioxide emitted from the separation device60is sucked by this negative pressure. This suction causes flow of the carbon dioxide from the separation device60to the carbon dioxide sublimators5A,5B, so that sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B are promoted. Suction of the carbon dioxide is performed by utilizing the fluid having the cold heat, and thus a pump or the like for suction is not necessary and energy conservation can be achieved. This energy conservation further achieves suppression in increase in electric power cost and suppression in generation of further carbon dioxide for power generation.

As the fluid having the cold heat, there are provided for example, liquefied fuel and liquefied gas. The liquefied fuel is, for example, liquefied natural gas (LNG), liquid hydrogen, liquefied methane, and others. Natural gas as main material for city gas is imported in a form of LNG and then re-gasified in an LNG terminal and shipped by a gas pipeline. In regasification of the LNG, a large amount of cold heat energy is released, and thus the cold heat energy has attracted attention as unused energy. Accordingly, as mentioned above, utilizing the cold heat of the liquefied fuel for suction of the carbon dioxide results in good use of unused energy, so that a carbon dioxide recovery device can be made ecological. Herein, as the liquefied fuel, liquid hydrogen can be given other than the LNG. Further, the liquefied gas is, for example, liquid nitrogen and liquid oxygen. Furthermore, the fluid having the cold heat is not necessarily in a form of liquid but may be gas, slurry, and gas-liquid multiphase flow.

Further, the carbon dioxide recovery device1A according to the first embodiment is configured such that the separation device60is provided with the absorption tower2to bring to-be-separated gas including carbon dioxide and the absorbing liquid for absorbing the carbon dioxide into gas-liquid contact to absorb the carbon dioxide by the absorbing liquid and the regeneration tower3configured to emit the carbon dioxide with the water vapor from the absorbing liquid that has absorbed the carbon dioxide. The regeneration tower3, the water vapor condensers4A,4B to condense the water vapor that has been emitted in the regeneration tower3, the carbon dioxide sublimators5A,5B to sublimate (solidify) the carbon dioxide that has been emitted in the regeneration tower are successively connected in series. The water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B are connected to the refrigerant circuits12A,12B using the fluid having the cold heat as the refrigerant, and the water vapor is condensed and the carbon dioxide is sublimated (solidified) by the refrigerant. The water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B are depressurized to be under negative pressure when the water vapor is condensed and the carbon dioxide is sublimated (solidified), so that the water vapor and the carbon dioxide both having been emitted in the regeneration tower3are sucked.

According to the above-mentioned carbon dioxide recovery device1A, the regeneration tower3, the water vapor condensers4A,4B, and the carbon dioxide sublimators5A,5B are successively connected in series, and therefore, the carbon dioxide and the water vapor having been emitted in the regeneration tower3firstly flow in the water vapor condensers4A,4B and only the water vapor is cooled by the refrigerant utilizing the fluid having the cold heat and condensed in the water vapor condensers4A,4B. Then, only the carbon dioxide flows into the subsequent carbon dioxide sublimators5A,5B. The carbon dioxide having reached the carbon dioxide sublimators5A,5B is cooled by the refrigerant utilizing the fluid having the cold heat and sublimated (solidified). The dry ice generated by sublimating (solidifying) this carbon dioxide is recovered by sublimating (gasifying) again so as to be made good use of as the carbon dioxide gas or the like.

When the carbon dioxide is sublimated (solidified), the water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B are depressurized to be under the negative pressure. By this negative pressure, the water vapor and the carbon dioxide having been emitted in the regeneration tower3are sucked, so that the water vapor is made to flow from the regeneration tower3to the water vapor condensers4A,4B and the carbon dioxide is made to flow from the regeneration tower3through the water vapor condensers4A,4B to the carbon dioxide sublimators5A,5B.

In accordance with depressurizing of the water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B, the regeneration tower3connected in series is also depressurized, so that the boiling temperature of the absorbing liquid (amine-based solvents) in the regeneration tower3is lowered. Therefore, it is possible to suppress the energy consumption for heating the absorbing liquid (amine-based solvents).

Further, depressurizing of the regeneration tower3is made by utilizing the fluid having the cold heat, and thus electric power for depressurizing the regeneration tower3is unnecessary, thereby achieving energy conservation. The achievement in the energy conservation further achieves suppression of further generation of carbon dioxide for power generation.

Further, the carbon dioxide recovery device1A according to the first embodiment is configured such that the refrigerant circuits12A,12B are connected as being communicated with the carbon dioxide sublimators5A,5B, the water vapor condensers4A,4B, and the absorption tower2. The refrigerant flows through the carbon dioxide sublimators5A,5B, the water vapor condensers4A,4B, and the absorption tower2in this order.

According to the above-mentioned carbon dioxide recovery device1A, the refrigerant of the fluid having the cold heat that has been utilized for sublimation (solidification) of the carbon dioxide can be further used for condensation of the water vapor and used for cooling the absorption tower2thereafter. The absorption tower2is cooled down for the purpose of suppressing the temperature increase in the absorption tower2which is heated by the heat generated when the absorbing liquid (amino-based solvents) absorbs the carbon dioxide.

Further, the carbon dioxide recovery device1A according to the first embodiment is configured such that the regeneration tower3is connected in parallel with at least the two carbon dioxide recovery lines10A,10B configured with the water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B which are connected in series. Accordingly, it is possible to further efficiently recover the carbon dioxide.

In the carbon dioxide sublimators5A,5B, dry ice, which is the sublimated (solidified) carbon dioxide, needs to be recovered by regasification or the like, and thus in recovery, sublimation (solidification) of the carbon dioxide needs to be interrupted. To address this, the regeneration tower3is connected in parallel with at least the two carbon dioxide recovery lines10A,10B configured with the water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B which are connected in series, and accordingly, while one of the carbon dioxide recovery lines10A,10B is recovering the dry ice by sublimating (gasifying) the dry ice again through the carbon dioxide sublimator, the other one of the carbon dioxide recovery lines10A,10B can be kept operating. This achieves further efficient recovery of the carbon dioxide.

Further, the carbon dioxide recovery device1A according to the first embodiment is configured with the decompression valve9between the regeneration tower3and the water vapor condensers4A,4B. The more the pressure is lowered by cooling the carbon dioxide sublimators5A,5B, the more quickly the carbon dioxide can turn to the dry ice, and the force for sucking the emitted carbon dioxide and the water vapor can be increased. However, decrease in the pressure of the carbon dioxide sublimators5A,5B leads to decrease in the pressure of the regeneration tower3, so that the excessive decrease in the pressure inside the regeneration tower3could cause coexistence state of liquid and solid of the absorbing liquid (amino-based solvents) in the regeneration tower3, which could rather degrade the efficiency in emission of the carbon dioxide. To address this, it is preferable to provide the decompression valve between the regeneration tower3and the water vapor condensers4A,4B to enable adjustment of the pressure of the regeneration tower3by the decompression valve9.

Further, the carbon dioxide recovery device1A according to the first embodiment is configured such that when the to-be-separated gas is the combustion exhaust gas from an iron manufacturing plant or a cement plant, for example, the carbon dioxide sublimators5A,5B are cooled down by the refrigerant to about minus 85 degrees centigrade or below, when the to-be-separated gas is the combustion exhaust gas from a power plant, the carbon dioxide sublimators5A,5B are cooled down by the refrigerant to about minus 96 degrees centigrade or below, and when the to-be-separated gas is the atmosphere, the carbon dioxide sublimators5A,5B are cooled down by the refrigerant to about minus 140 degrees centigrade or below.

The temperature at which the carbon dioxide is in the gas-solid balanced state differs depending on the partial pressure of the carbon dioxide in the to-be-separated gas. Accordingly, by making the temperature inside the carbon dioxide sublimator to the temperature at which the gas-solid balanced state corresponding to the partial pressure value is kept, sublimation (solidification) of the carbon dioxide is started, and thus the carbon dioxide sublimators5A,5B can be kept under the negative pressure. Thereby, the water vapor and the carbon dioxide which have been emitted in the regeneration tower3can be sucked.

Second Embodiment

Next, a second embodiment of a carbon dioxide recovery device according to the present invention is explained with focus on different points from the carbon dioxide recovery device1A according to the first embodiment with reference to the accompanying drawings.

FIG.2is a schematic view showing a configuration of a carbon dioxide recovery device1B according to the second embodiment. The configuration of the absorption tower2and the regeneration tower3is the same as the carbon dioxide recovery device1A according to the first embodiment. The regeneration tower3is connected with one water vapor condenser4in series via a first transfer pipe L15. Then, the water vapor condenser4is connected with a second transfer pipe L16to discharge carbon dioxide to the carbon dioxide sublimators5A,5B.

The second transfer pipe L16is branched off to a branch transfer pipe L161A and a branch transfer pipe L161B by a switching valve18. By this branching, the water vapor condenser4is connected in parallel with the carbon dioxide sublimator5A and the carbon dioxide sublimator5B. Operation of the switching valve18enables selection of either one of the carbon dioxide sublimators5A,5B through which carbon dioxide, which has been discharged from the regeneration tower3and has passed through the water vapor condenser4, flows. Further, open-close valves14A,14B are provided on the branch transfer pipes L161A, L161B, respectively.

The carbon dioxide sublimators5A,5B are communicated with the refrigerant circuits12A,12B which utilize the cold heat in regasification of liquefied fuel as the refrigerant, respectively. The refrigerant circuits12A,12B each having passed through the carbon dioxide sublimators5A,5B are merged so that the refrigerant having flown through the carbon dioxide sublimators5A,5B further flows through the water vapor condenser4and the absorption tower2in this order.

According to the above-mentioned carbon dioxide recovery device1B, too, when carbon dioxide is sublimated (solidified) in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to become under negative pressure. Thus, the carbon dioxide sublimator5A (5B) functions as a pump, and thereby the water vapor and the carbon dioxide that have been emitted in the regeneration tower3are sucked. This suction causes flow of the water vapor from the regeneration tower3to the water vapor condenser4and causes flow of the carbon dioxide from the regeneration tower3through the water vapor condenser4to the carbon dioxide sublimator5A (5B).

Further, in accordance with decompression of the carbon dioxide sublimator5A (5B), the regeneration tower3connected in series is also decompressed, so that the boiling temperature of the absorbing liquid in the regeneration tower3is lowered. Therefore, the consumption energy for heating the absorbing liquid can be suppressed.

Further, when the carbon dioxide having turned into dry ice is to be recovered from the carbon dioxide sublimator5A (5B), sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimator5A (5B) needs to be stopped. However, the switching valve18makes it possible to select either one of the carbon dioxide sublimators5A,5B through which the carbon dioxide, which has been discharged from the regeneration tower3and has passed through the water vapor sublimator4, flows. Accordingly, when the carbon dioxide is to be recovered from the one carbon dioxide sublimator5A, the other carbon dioxide sublimator5B can keep performing sublimation (solidification) of the carbon dioxide. Therefore, the carbon dioxide can be recovered more efficiently.

As mentioned above, the carbon dioxide recovery device1B according to the second embodiment is configured such that the regeneration tower3is connected with the one water vapor condenser4, and the water vapor condenser4is connected in parallel with at least the two carbon dioxide sublimators5A,5B.

According to the above-mentioned carbon dioxide recovery device1B, the regeneration tower3is connected with the one water vapor condenser4, and the water vapor condenser4is connected in parallel with at least the two carbon dioxide sublimators5A,5B. Accordingly, when the dry ice is to be recovered by one of the carbon dioxide sublimators5A,5B by regasification and others, the other one of the carbon dioxide sublimators5A,5B may be kept operating, achieving further efficient recovery of the carbon dioxide.

Third Embodiment

Next, a third embodiment of a carbon dioxide recovery device according to the present invention is explained in detail with reference to the accompanying drawings.FIG.3is a schematic view of a configuration of a carbon dioxide recovery device50A according to the third embodiment.

The carbon dioxide recovery device50A is provided with separation devices70A,70B and the carbon dioxide sublimators5A,5B as shown inFIG.3. The separation device70A is connected in series with the carbon dioxide sublimator5A, and the separation device70B is connected in series with the carbon dioxide sublimator5B. Herein, the separation device70A and the separation device70B are the same devices, and the carbon dioxide sublimator5A and the carbon dioxide sublimator5B are the same devices.

The separation devices70A,70B are stored inside with adsorbents701A,701B to adsorb carbon dioxide. As the adsorbent, for example, there are used zeolite (for example, a molecular sieve 13X of UNION SHOWA K.K., and NSA-700 of Tosoh Corporation), amino-impregnated solid sorbent (porous substance carried with amine compound), gate-type sorbent (ELM-11 [Cu (bpy)2(BF4)2], and others. The separation devices70A,70B are provided with gas introduction ports702A,702B below the sorbents701A,701B, respectively, and the gas introduction ports702A,702B are connected with a gas supply passage L11to supply the combustion exhaust gas (one example of the to-be-separated gas) to the separation devices70A,70B. To be more specific, the gas supply passage L11is branched off by a switching valve19to a branch gas supply passage L111and a branch gas supply passage L112, and the branch gas supply passage L111is connected to the gas introduction port702A of the separation device70A and the branch gas supply passage L112is connected to the gas introduction port702B.

The branch gas supply passage L111is provided with an open-close valve20A and the branch gas supply passage L112is provided with an open-close valve20B, and the combustion exhaust gas is supplied to the separation devices70A,70B by bringing the open-close valves20A,20B in a valve-open state. This combustion exhaust gas is the one utilizing the combustion exhaust gas generated in power generation and natural gas purification and the combustion exhaust gas generated from a combustor, a blast furnace, and others. The combustion exhaust gas includes about 10 to 20% of carbon dioxide and further includes nitrogen, oxygen, and others.

Further, the gas supply passage L11is branched off by the switching valve19so that the gas supply passage L11is connected in parallel with a carbon dioxide recovery line500A and a carbon dioxide recovery line500B. The carbon dioxide recovery line500A is configured such that the separation device70A and the carbon dioxide sublimator5A are connected in series in this order from an upstream side of supplying the combustion exhaust gas. The carbon dioxide recovery line500B is configured such that the separation device70B and the carbon dioxide sublimator5B are connected in series in this order from the upstream side of supplying the combustion exhaust gas. Operation of the switching valve19makes it possible to select either one of the carbon dioxide recovery line500A and the carbon dioxide recovery line500B through which the combustion exhaust gas supplied from the gas supply passage L11is made flow.

The combustion exhaust gas supplied from the gas introduction port702A (702B) ascends in the separation device70A (70B) and comes to contact with the adsorbent701A (701B) stored in the separation device70A (70B). Then, the adsorbent701A (701B) selectively adsorbs the carbon dioxide included in the combustion exhaust gas. By this adsorption, the carbon dioxide is separated from the combustion exhaust gas. Herein, the adsorbent701A (701B) such as zeolite has a concern about degradation in the adsorption performance when the adsorbent takes in moisture, and thus it is conceivable to provide a water vapor removal device (not shown) on the gas supply passage L11and supply the combustion exhaust gas, which has been removed with the water vapor by the water vapor removal device, to the separation device70A (70B). Further, the combustion exhaust gas is conceived to include sulfur oxide, and thus a desulfurization unit (not shown) may be provided on the gas supply passage L11so that the combustion exhaust gas which has been removed with the sulfur oxide is supplied to the separation device70A (70B).

Then, the combustion exhaust gas (nitrogen and oxygen) which has been separated from the carbon dioxide is discharged from a discharge port704A (704B) provided on a top portion of the separation device70A (70B) to a discharge passage L12A (L12B).

The adsorbent701A (701B) has its determined capacity of adsorbable amount of carbon dioxide by its volume or the like, and thus the adsorbent701A (701B) which has absorbed a certain amount of the carbon dioxide cannot further adsorb the carbon dioxide. Accordingly, in order to adsorb further carbon dioxide, the adsorbent701A (701B) needs to be desorbed. The desorption needs to be performed by placing the adsorbent701A (701B) under the decompressed state, and accordingly, inside of the separation device70A (70B) is decompressed. The carbon dioxide desorbed from the adsorbent701A (701B) is diffused from a diffusion port703A (703B) provided on atop portion of the separation device70A (70B). Then, the adsorbent701A (701B) that has been desorbed from the carbon dioxide is brought into contact with the combustion exhaust gas supplied from the gas introduction port702A (702B) so that the adsorbent701A (701B) can adsorb further carbon dioxide.

The diffusion port703A (703B) is connected with the transfer pipe L15A (L15B), and the carbon dioxide diffused from the diffusion port703A (703B) is discharged to the transfer pipe L15A. This discharge is performed by sucking the carbon dioxide by the negative pressure generated in the carbon dioxide sublimator5A (5B) (the negative pressure generated in the carbon dioxide sublimator5A (5B) will be explained below).

The carbon dioxide sublimator5A (5B) is connected with the separation device70A (70B) via the transfer pipe L15A (L15B) so that the carbon dioxide diffused from the separation device70A (70B) can flow to the carbon dioxide sublimator5A (5B). The transfer pipe L15A is provided with a decompression valve9A and an open-close valve14A in this order from an upstream side between the separation device70A and the carbon dioxide sublimator5A, and the transfer pipe L15B is provided with a decompression valve9B and an open-close valve14B between the separation device70B and the carbon dioxide sublimator5B. Herein, the decompression valve9A and the decompression valve9B are identical devices, and the open-close valve14A and the open-close valve14B are identical devices.

The carbon dioxide sublimator5A (5B) is provided inside with a heat exchanger51A (51B). The heat exchanger51A (51B) is used for cooling the carbon dioxide therein by use of the refrigerant flowing through the refrigerant circuit12A (12B). The carbon dioxide sublimator5A (5B) is further connected with a heat pump52A (52B) utilizing waste heat and ambient heat, a drain53A (53B), and a take-out pipe54A (54B). The drain53A (53B) is provided with an open-close valve16A (16B), and the take-out pipe54A (54B) is provided with an open-close valve17A (17B).

The refrigerant circuit12A (12B) is configured to make the refrigerant flow inside the carbon dioxide sublimator5A (5B). As the refrigerant, the cold heat after regasification of liquefied fuel (one example of fluid) is used. The liquefied fuel is, for example, exemplified by liquefied natural gas, liquid hydrogen, and liquefied methane. Further, as the refrigerant, the cold heat after regasification of the liquefied gas may be used. The liquefied gas is, for example, exemplified by liquefied nitrogen and liquefied oxygen.

Function of the refrigerant and the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery device50A having the above-mentioned configuration is explained below.

The refrigerant passes through the refrigerant circuit12A (12B) to cool the inside of the carbon dioxide sublimator5A (5B) by the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B). When liquefied natural gas is used as the liquefied fuel, the cold heat is minus 162 degrees centigrade, and when liquid hydrogen is used, the cold heat is minus 253 degrees centigrade. The temperature inside the carbon dioxide sublimator5A (5B) is however cooled to a temperature appropriate for sublimation (solidification) of the carbon dioxide by controlling a temperature gap by the heat exchanger51A (51B) or by utilizing a separate operation medium or a refrigerant. For example, when combustion exhaust gas from an iron manufacturing plant or a cement plant is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 85 degrees centigrade or below. Further, when combustion exhaust gas from a power plant is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 96 degrees centigrade or below. Furthermore, when the atmosphere is used as the to-be-separated gas, the temperature inside the carbon dioxide sublimator5A (5B) is preferably cooled to about minus 140 degrees centigrade or below.

By cooling down the temperature inside the carbon dioxide sublimator5A (5B) to the temperature appropriate for sublimation (solidification) of the carbon dioxide, the carbon dioxide in the carbon dioxide sublimator5A (5B) is sublimated (solidified) to become dry ice. In sublimation (solidification), there is a case that a minute amount of moisture remains in the carbon dioxide sublimator5A (5B), but the thus remaining moisture is discharged from the drain53A (53B) by opening the open-close valve16A (16B). Further, when the carbon dioxide that has become dry ice is to be recovered, the open-close valve17A (17B) is opened to bring the carbon dioxide sublimator5A (5B) back to the normal temperature so that the dry ice is sublimated (gasified) and recovered from the take-out pipe54A (54B). At this time, the open-close valves14A (14B),16A (16B) are in a valve-closed state so that the sublimated (gasified) carbon dioxide would not flow in any parts other than the take-out pipe54A (54B). Then, the thus recovered carbon dioxide is utilized as carbon dioxide gas or the like.

Further, when the carbon dioxide is to be recovered, sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B needs to be interrupted. However, as mentioned above, it is selectable to make flow the combustion exhaust gas supplied from the gas supply passage L11into either one of the carbon dioxide recovery lines500A,500B by the switching valve19. Accordingly, while the carbon dioxide is being recovered from the carbon dioxide sublimator5A of the one carbon dioxide recovery line500A, the carbon dioxide sublimator5B of the other one carbon dioxide recovery line500B can continuously sublimate (solidify) the carbon dioxide, and vice versa. Therefore, the carbon dioxide can be further efficiently recovered.

When sublimation (solidification) of the carbon dioxide is performed in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to be under negative pressure. Thereby, the carbon dioxide sublimator5A (5B) functions as a pump to perform suction of the carbon dioxide that have been diffused from the separation device70A (70B). This suction creates flow of the carbon dioxide from the separation device70A (70B) to the carbon dioxide sublimator5A (5B), so that sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimator5A (5B) is promoted.

While desorption of the adsorbent701A (701B) is performed under the decompressed state, in accordance with decompression of the carbon dioxide sublimator5A (5B), the separation device70A (70B) connected in series with the carbon dioxide sublimator5A (5B) is also depressurized to about 4 kPa. Accordingly, there is no need to provide a pump or the like to depressurize the separation device70A (70B). In other words, no electric power for operating a pump or the like is required, thereby achieving energy conservation. Then, conservation in energy can achieve suppression of increase in the electric power cost and suppression of generation of further carbon dioxide for power generation. Herein, the pressure of the separation device70A (70B) is adjusted by the decompression valve9A (9B) provided on the transfer pipe L15A (L15B).

Modified Example of Third Embodiment

Next, a carbon dioxide recovery device50B according to a modified example of the third embodiment is explained with reference toFIG.4.FIG.4is a schematic view of a configuration of the carbon dioxide recovery device50B according to the modified example of the third embodiment.

The carbon dioxide recovery line500A (500B) of the carbon dioxide recovery device50A according to the above-mentioned third embodiment is configured with the separation device70A (70B) and the carbon dioxide sublimator5A (5B) which are connected in series. On the other hand, a carbon dioxide recovery line500C (500D) in the carbon dioxide recovery device50B is configured with the separation device70A (70B), the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) connected in series in this order from an upstream side of supplying the combustion exhaust gas.

There is a concern about the adsorbent701A (701B) such as zeolite, about decline in adsorption performance when it adsorbs moisture, and thus the carbon dioxide recovery device50A is configured such that the combustion exhaust gas that has been removed with water vapor in advance is supplied to the separation device70A (70B). However, in recent years, an adsorbent, which hardly lowers its adsorption performance even after the adsorbent adsorbs moisture, has been studied and developed. When such an adsorbent (for example, amine-impregnated solid sorbent) is used for the separation device70A (70B), it is conceivable to supply the combustion exhaust gas including water vapor to the separation device70A (70B).

When the combustion exhaust gas including the water vapor is to be supplied to the separation device70A (70B), in diffusing the carbon dioxide from the separation device70A (70B), it is assumed that the water vapor is diffused with the carbon dioxide. If the water vapor is solidified with the carbon dioxide in the carbon dioxide sublimator5A (5B), recovery of the carbon dioxide becomes difficult. To address this, the separation device70A (70B), the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) are connected in series as the carbon dioxide recovery device50B so that the carbon dioxide and the water vapor diffused from the separation device70A (70B) firstly flow in the water vapor condenser4A (4B) and only the water vapor is cooled by the refrigerant and condensed in the water vapor condenser4A (4B). The water vapor is firstly condensed, and accordingly only the carbon dioxide flows to the subsequent carbon dioxide sublimator5A (5B) and is cooled by the refrigerant and sublimated (solidified) in the carbon dioxide sublimator5A (5B). Thus, recovery of the carbon dioxide is made easily.

The separation device70A (70B) stores the adsorbent701A (701B) therein. The adsorbent is the one hardly lowering its adsorption performance of adsorbing the carbon dioxide even if the moisture (for example, amine-impregnated solid sorbent) is included. Other configuration of the separation device70A (70B) is identical with the separation device70A (70B) of the carbon dioxide recovery device50A, and thus its explanation is omitted.

The separation device70A (70B) is connected with the water vapor condenser4A (4B) via the first transfer pipe L15A (L15B) so that the carbon dioxide and the water vapor which are diffused from the separation device70A (70B) are allowed to flow in the water vapor condenser4A (4B). Herein, the first transfer pipe L15A is provided with the decompression valve9A and the open-close valve13A in this order from the upstream side between the separation device70A and the water vapor condenser4A. The first transfer pipe L15B is provided with the decompression valve9B and the open-close valve13B in this order from the upstream side between the separation device70B and the water vapor condenser4B.

The water vapor condenser4A (4B) is provided with the heat exchanger41A (41B) inside. The heat exchanger41A is used for cooling the water vapor and the carbon dioxide that have reached the water vapor condenser4A (4B) from the separation device70A (70B) by the refrigerant flowing in the refrigerant circuit12A (12B). The water vapor condenser4A (4B) is further connected with the heat pump42A (42B) utilizing the waste heat and the ambient heat and the drain43A (43B). The drain43A (43B) includes the open-close valve15A (15B).

Further, the water vapor condenser4A (4B) is connected with the carbon dioxide sublimator5A (5B) via the second transfer pipe L16A (L16B). Further, the second transfer pipe L16A (L16B) is provided with the open-close valve14A (14B) between the water vapor condenser4A (4B) and the carbon dioxide sublimator5A (5B).

The carbon dioxide sublimator5A (5B) is a device identical with the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery device50A to sublimate (solidify) the carbon dioxide by the refrigerant flowing in the refrigerant circuit12A (12B) by use of the heat exchanger51A (51B) provided therein.

The refrigerant circuit12A (12B) is configured to make flow the refrigerant in the order of the carbon dioxide sublimator5A (5B) and the water vapor condenser4A (4B). The one used for the refrigerant is the cold heat after regasification of the liquefied fuel (one example of fluid) as similar to the carbon dioxide recovery device50A.

Function of the refrigerant, the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery device50B having the above-mentioned configuration is explained below.

The refrigerant passes through the refrigerant circuit12A (12B) to firstly cool the inside of the carbon dioxide sublimator5A (5B) to the temperature appropriate for sublimation (solidification) of the carbon dioxide by the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B) so that the carbon dioxide in the carbon dioxide sublimator5A (5B) is sublimated (solidified). This is similar to the carbon dioxide recovery device50A. Herein, the temperature appropriate for sublimation (solidification) of the carbon dioxide is about minus 85 degrees centigrade or below when the combustion exhaust gas from an iron manufacturing plant or a cement plate is used as the to-be-separated gas, about minus 96 degrees centigrade or below when the combustion exhaust gas from a power plant is used as the to-be-separated gas, and about minus 140 degrees centigrade or below when the atmosphere is used as the to-be-separated gas.

When sublimation (solidification) of the carbon dioxide is performed in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to be under negative pressure. Thereby, the carbon dioxide sublimator5A (5B) functions as a pump to perform suction of the water vapor and the carbon dioxide that have been diffused from the separation device70A (70B). This suction creates flow of the water vapor and the carbon dioxide toward the water vapor condenser4A (4B) and the carbon dioxide sublimator5A (5B).

Further, in association with decompression of the carbon dioxide sublimator5A (5B), the separation device70A (70B) connected in series with the carbon dioxide sublimator5A (5B) is depressurized to about 4 kPa, which is similar to the carbon dioxide recovery device50A.

After cooling inside the carbon dioxide sublimator5A (5B), the refrigerant flows to the water vapor condenser4A (4B) to cool the inside of the water vapor condenser4A (4B) by the heat exchanger41A (41B) of the water vapor condenser4A (4B). The temperature of the refrigerant has increased by heat exchanging in the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B), and thus inside the water vapor condenser4A (4B) is cooled down to about 1 degree centigrade.

Since the water vapor condenser4A (4B) is about 1 degree centigrade, the carbon dioxide and the water vapor which are sucked by the negative pressure generated in the carbon dioxide sublimator5A (5B) and discharged from the separation device70A (70B) are made to flow into the water vapor condenser4A (4B) to be cooled down to about 20 degrees centigrade. Thereby, the water vapor is condensed to become water. The water is stored on a bottom part of the water vapor condenser4A (4B), and the thus stored water is discharged through the drain43A (43B) by opening the open-close valve15A (15B).

The carbon dioxide that has flown with the water vapor in the water vapor condenser4A (4B) remains as gaseous body in a temperature about 20 degrees centigrade, and accordingly, the carbon dioxide is sucked by the carbon dioxide sublimator5A (5B), so that the carbon dioxide passes through the second transfer pipe L16A (L16B) and flows in the carbon dioxide sublimator5A (5B). Then, the carbon dioxide having flown in the carbon dioxide sublimator5A (5B) is sublimated (gasified) as mentioned above.

As mentioned above, the carbon dioxide recovery device50A according to the third embodiment or the carbon dioxide recovery device50B according to the modified example is configured such that the separation devices70A,70B store the adsorbents701A,701B adsorbing carbon dioxide and is configured to separate the carbon dioxide from the to-be-separated gas by adsorbing the carbon dioxide included in the to-be-separated gas (for example, the combustion exhaust gas) that has been supplied to the separation devices70A,70B.

According to the above-mentioned carbon dioxide recovery devices50A,50B, the separation devices70A,70B store the adsorbent (such as zeolite, amine-impregnated solid sorbent, and gate-type sorbent)701A,701B that can adsorb the carbon dioxide, respectively, and accordingly, the carbon dioxide can be separated from the to-be-separated gas by adsorbing the carbon dioxide included in the to-be-separated gas. Then, the carbon dioxide adsorbed by the adsorbents701A,701B can be recovered by desorbing from the adsorbents701A,701B. This desorption is generally performed under the depressurized state, but the separation devices70A,70B connected in series with the carbon dioxide sublimators5A,5B are also decompressed in accordance with decompression of the carbon dioxide sublimators5A,5B by the refrigerant, and accordingly, there is no need to provide a pump or the like to decompress the separation devices70A,70B. In other words, electric power for operating the pump or the like is not necessary, thereby achieving energy conservation. The energy conservation further achieves suppression of increase in the electric power cost and suppression of generation of further carbon dioxide for power generation.

Further, the carbon dioxide recovery device50A according to the third embodiment and the carbon dioxide recovery device50B according to the modified example are configured such that the separation devices70A,70B are configured to emit water vapor with the carbon dioxide. The carbon dioxide recovery devices50A,50B include the water vapor condensers4A,4B to condense the water vapor. The separation devices70A,70B, the water vapor condensers4A,4B, and the carbon dioxide sublimators5A,5B are connected in series in order from an upstream side of supplying the to-be-separated gas (for example, the combustion exhaust gas). The refrigerant circuits12A,12B are connected to the water vapor condensers4A,4B and the carbon dioxide sublimators5A,5B, respectively, and the water vapor is condensed and the carbon dioxide is sublimated (solidified) by the refrigerant.

When the water vapor is emitted with the carbon dioxide from the separation devices70A,70B, recovery of the carbon dioxide becomes difficult if the water vapor is solidified with the carbon dioxide in the carbon dioxide sublimators5A,5B. To address this, as the carbon dioxide recovery devise50B, the separation devices70A,70B, the water vapor condensers4A,4B, and the carbon dioxide sublimators5A,5B are connected in series, respectively, so that the carbon dioxide and the water vapor emitted from the separation devices70A,70B first flow to the water vapor condensers4A,4B, and only the water vapor is cooled by the refrigerant and condensed in the water vapor condenser. The water vapor is first condensed, and thus only the carbon dioxide flows to the subsequent carbon dioxide sublimators5A,5B to be cooled by the refrigerant and sublimated (solidified) in the carbon dioxide sublimators5A,5B. Thereby, recovery of the carbon dioxide is made easily.

Page 31:

Fourth Embodiment

Next, a carbon dioxide recovery device100A according to a fourth embodiment is explained with reference toFIG.5as for different features from the carbon dioxide recovery devices50A,50B according to the third embodiment.FIG.5is a schematic view of a configuration of the carbon dioxide recovery device100A according to the fourth embodiment.

The carbon dioxide recovery device100A is provided with a separation device80and the carbon dioxide sublimators5A,5B. The two carbon dioxide sublimators5A,5B are the identical devices.

The separation device80retains a permeable membrane803therein to selectively transmit carbon dioxide. As the permeable membrane803, for example, an inorganic membrane such as a zeolite membrane (such as a high silica CHA zeolite membrane and DDR zeolite membrane) and an organic membrane such as a molecular gate membrane are used. This permeable membrane803divides inside of the separation device80into a non-transmission side801and a transmission side802. The non-transmission side801is provided with a gas introduction port804, and the gas introduction port804is connected with the gas supply passage L11. Thus, the combustion exhaust gas can be supplied to the separation device80(the non-transmission side801). Herein, the combustion exhaust gas to be supplied to this separation device80(the non-transmission side801) is the one that has been removed with water vapor and sulfur oxide by a not-shown water vapor removal device and a not-shown desulfurization device which are provided on the gas supply passage L11.

The transmission side802is used to selectively transmit the carbon dioxide. Namely, among components included in the combustion exhaust gas to be supplied to the separation device80(the non-transmission side801), only carbon dioxide can move to the transmission side802, and nitrogen and oxygen other than the carbon dioxide are not allowed to transmit the permeable membrane803and reside in the non-transmission side801.

Further, the non-transmission side801is provided with a discharge port806, and the discharge port806is connected with a discharge passage L12to discharge nitrogen, oxygen, and others remaining in the non-transmission side801. Furthermore, the discharge passage L12includes an open-close valve81.

The transmission side802is provided with a diffusion port805to diffuse the carbon dioxide that has passed through the permeable membrane803. The diffusion port805is connected with a transfer pipe L15so that the carbon dioxide diffused from the discharge port805is discharged to the transfer pipe L15. This discharge is performed by suction of the carbon dioxide sucked by the negative pressure generated in the carbon dioxide sublimator5A (5B).

The transfer pipe L15is branched off by the switching valve11to the branch transfer pipe L151A and the branch transfer pipe L151B. By this branching, the separation device80(the transmission side802) is connected with the carbon dioxide sublimator5A via the transfer pipe L15and the branch transfer pipe L151A and connected with the carbon dioxide sublimator5B via the transfer pipe L15and the branch transfer pipe L151B. Then, operation of the switching valve11makes it possible to select either one of the carbon dioxide sublimators5A,5B through which the carbon dioxide discharged from the separation device80flows. Herein, the branch transfer pipe L151A (L151B) is provided with an open-close valve14A (14B) between the switching valve11and the carbon dioxide sublimator5A (5B).

The carbon dioxide sublimator5A (5B) is identical with the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery devices50A,50B and is configured to sublimate (solidify) the carbon dioxide by the refrigerant flowing in the refrigerant circuit12A (12B) by use of the heat exchanger51A (51B) inside the device. The refrigerant circuit12A (12B) is also identical with the refrigerant circuit12A (12B) in the carbon dioxide recovery device50A, and thus explanation thereof is omitted.

Function of the refrigerant and the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery device100A having the above-mentioned configuration is explained below.

The refrigerant passes through the refrigerant circuit12A (12B) to cool the inside of the carbon dioxide sublimator5A (5B) to the temperature appropriate for sublimation (solidification) of the carbon dioxide by the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B) so that the carbon dioxide in the carbon dioxide sublimator5A (5B) is sublimated (solidified). This is similar to the carbon dioxide recovery device50A. Herein, the temperature appropriate for sublimation (solidification) of the carbon dioxide is about minus 85 degrees centigrade or below when the combustion exhaust gas from an iron manufacturing plant or a cement plant is used as the to-be-separated gas, about minus 96 degrees centigrade or below when the combustion exhaust gas from a power plant is used as the to-be-separated gas, and about minus 140 degrees centigrade or below when the atmosphere is used as the to-be-separated gas.

When the carbon dioxide is to be recovered, sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B needs to be interrupted. However, as mentioned above, it is selectable to make flow the combustion exhaust gas discharged from the separation device80into either one of the carbon dioxide sublimators5A,5B by the switching valve11. Accordingly, while the carbon dioxide is being recovered from the one carbon dioxide sublimator5A, the other carbon dioxide sublimator5B can continuously sublimate (solidify) the carbon dioxide, and vice versa. Therefore, the carbon dioxide can be further efficiently recovered.

When sublimation (solidification) of the carbon dioxide is performed in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to be under negative pressure. Thereby, the carbon dioxide sublimator5A (5B) functions as a pump to perform suction of the carbon dioxide that have been diffused from the separation device80. This suction creates flow of the carbon dioxide from the separation device80to the carbon dioxide sublimator5A (5B), so that sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimator5A (5B) is promoted.

While the carbon dioxide sublimator5A (5B) is decompressed, the separation device80(the transmission side802) connected in series with the carbon dioxide sublimator5A (5B) is also depressurized to about 4 kPa. Accordingly, even if a pump or the like to depressurize the separation device80(the transmission side802) is not provided, the carbon dioxide included in the combustion exhaust gas supplied to the non-transmission side801of the separation device80is sucked by the transmission side802, so that separation of the carbon dioxide is promoted. In other words, no electric power for operating the pump or the like is required, thereby achieving energy conservation. Then, conservation in energy can achieve suppression of increase in the electric power cost and achieve suppression of generation of further carbon dioxide for power generation. The pressure of the separation device80is adjusted by the decompression valve9provided on the transfer pipe L15. Herein, when this separation of carbon dioxide is to be performed, the open-close valve18is closed to prevent backflow from the discharge passage L12to the separation device80. Then, in a case when the non-transmission side801is filled with nitrogen, oxygen, and others other than the carbon dioxide and no any further combustion exhaust gas is allowed to be supplied to the non-transmission side801, the open-close valve81is opened to discharge the nitrogen, oxygen, and others.

Modified Example of Fourth Embodiment

Next, a carbon dioxide recovery device100B according to a modified example of the fourth embodiment is explained in detail with reference toFIG.6.FIG.6is a schematic view of a configuration of the carbon dioxide recovery device100B according to the modified example of the fourth embodiment.

The carbon dioxide recovery device100B is configured with the separation device80, the carbon dioxide recovery line10A in which the water vapor condenser4A and the carbon dioxide sublimator5A are connected in series, and the carbon dioxide recovery line10B in which the water vapor condenser4B and the carbon dioxide sublimator5B are connected in series.

When combustion exhaust gas including water vapor is supplied to the separation device80, in performing diffusion of the carbon dioxide from the separation device80, it is assumed that the water vapor could be diffused with the carbon dioxide. If the water vapor is solidified with the carbon dioxide in the carbon dioxide sublimator5A (5B), recovery of the carbon dioxide becomes difficult. To address this, as the carbon dioxide recovery device100B, the separation device80, the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) are connected in series so that the carbon dioxide and the water vapor diffused from the separation device80firstly flow in the water vapor condenser4A (4B), and only the water vapor is cooled down by the refrigerant and condensed in the water vapor condenser4A (4B). The water vapor is firstly condensed, and thus only the carbon dioxide flows to the subsequent carbon dioxide sublimator5A (5B) and only this carbon dioxide is cooled by the refrigerant and sublimated (solidified) in the carbon dioxide sublimator5A (5B). Thereby, recovery of the carbon dioxide is made easy.

The separation device80is the one identical with the separation device80in the above-mentioned carbon dioxide recovery device100A. The carbon dioxide and the water vapor diffused from the separation device80are discharged to the first transfer pipe L15. This discharge is made by sucking the carbon dioxide and the water vapor by the negative pressure generated in sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B.

The first transfer pipe L15is branched off by the switching valve11to the branch transfer pipe L151A and the branch transfer pipe L151B. By this branching of the pipe, the separation device80(the transmission side802) is connected with the carbon dioxide recovery line10A formed of the water vapor condenser4A and the carbon dioxide sublimator5A via the first transfer pipe L15and the branch transfer pipe L51A and connected with the carbon dioxide recovery line10B formed of the water vapor condenser4B and the carbon dioxide sublimator5B via the first transfer pipe L15and the branch transfer pipe L151B. Then, operation of the switching valve11allows selection of flow of the carbon dioxide and the water vapor which are diffused from the separation device80(the transmission side802) to either one of the carbon dioxide recovery lines10A and10B. Herein, the branch transfer pipe L151A (L151B) is provided with the open-close valve13A (13B) between the switching valve11and the water vapor condenser4A (4B).

The water vapor condenser4A (4B) is the one identical with the water vapor condenser4A (4B) in the carbon dioxide recovery device50B to condense the water vapor by the refrigerant flowing in the refrigerant circuit12A (12B) by use of the heat exchanger41A (41B) provided therein. The water vapor condenser4A (4B) is connected to the carbon dioxide sublimator5A (5B) via the second transfer pipe L16A (L16B). Herein, the second transfer pipe L16A (L16B) is provided with the open-close valve14A (14B) between the water vapor condenser4A (4B) and the carbon dioxide sublimator5A (5B).

The carbon dioxide sublimator5A (5B) is the one identical with the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery devices50A,50B, and100A to sublimate (solidify) the carbon dioxide by the refrigerant flowing in the refrigerant circuit12A (12B) by use of the heat exchanger51A (51B) provided therein.

Further, the refrigerant circuit12A (12B) is configured such that the refrigerant flows in an order of the carbon dioxide sublimator5A (5B) and the water vapor condenser4A (4B) as similar to the carbon dioxide recovery device50B. As the refrigerant, the cold heat formed by regasification of liquefied fuel (one example of fluid) is used as similar to the carbon dioxide recovery devices50A,50B, and100A.

Function of the refrigerant, the water vapor condenser4A (4B), and the carbon dioxide sublimator5A (5B) in the carbon dioxide recovery device100B having the above-mentioned configuration is explained below.

The refrigerant passes through the refrigerant circuit12A (12B) to firstly cool inside the carbon dioxide sublimator5A (5B) to the temperature appropriate for sublimation (solidification) of the carbon dioxide by the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B) so that the carbon dioxide in the carbon dioxide sublimator5A (5B) is sublimated (solidified). This is similar to the carbon dioxide recovery devices50A,50B, and100A. Herein, the temperature appropriate for sublimation (solidification) of the carbon dioxide is about minus 85 degrees centigrade or below when the combustion exhaust gas from an iron manufacturing plant or a cement plant is used as the to-be-separated gas, about minus 96 degrees centigrade or below when the combustion exhaust gas from a power plant is used as the to-be-separated gas, and about minus 140 degrees centigrade or below when the atmosphere is used as the to-be-separated gas as mentioned above.

When sublimation (solidification) of the carbon dioxide is performed in the carbon dioxide sublimator5A (5B), the carbon dioxide sublimator5A (5B) is depressurized to be under negative pressure. Thereby, the carbon dioxide sublimator5A (5B) functions as a pump to perform suction of the water vapor and the carbon dioxide that have been diffused from the separation device80. This suction generates flow of the water vapor and the carbon dioxide toward the water vapor condenser4A (4B) and the carbon dioxide sublimator5A (5B).

Further, in association with decompression of the carbon dioxide sublimator5A (5B), the separation device80connected in series is depressurized to about 4 kPa, which is similar to the carbon dioxide recovery device100A.

After cooling inside the carbon dioxide sublimator5A (5B), the refrigerant flows to the water vapor condenser4A (4B) to cool inside the water vapor condenser4A (4B) by the heat exchanger41A (41B) of the water vapor sublimator4A (4B). The temperature of the refrigerant increases by heat exchanging in the heat exchanger51A (51B) of the carbon dioxide sublimator5A (5B), and thus the inside of the water vapor condenser4A (4B) is cooled down to about 1 degree centigrade.

Since the water vapor condenser4A (4B) is about 1 degree centigrade, the carbon dioxide and the water vapor which are sucked by the negative pressure generated in the carbon dioxide sublimator5A (5B) and discharged from the separation device80(the transmission side802) are made to flow into the water vapor condenser4A (4B) to be cooled down to about 20 degrees centigrade. Thereby, the water vapor is condensed to become water. The water is stored on a bottom part of the water vapor condenser4A (4B), and the thus stored water is discharged through the drain43A (43B) by opening the open-close valve15A (15B).

The carbon dioxide that has flown with the water vapor in the water vapor condenser4A (4B) remains as gaseous body in a temperature about 20 degrees centigrade, and accordingly, the carbon dioxide is sucked by the carbon dioxide sublimator5A (5B) so that the carbon dioxide passes through the second transfer pipe L16A (L16B) and flows in the carbon dioxide sublimator5A (5B). Then, the carbon dioxide having flown in the carbon dioxide sublimator5A (5B) is sublimated (solidified) as mentioned above.

As explained above, the carbon dioxide recovery device100A according to the fourth embodiment and the carbon dioxide recovery device100B according to its modified example are configured such that the separation device80is provided with the permeable membrane803to selectively transmit carbon dioxide, and the permeable membrane803transmits the carbon dioxide included in the to-be-separated gas (such as combustion exhaust gas) that has been supplied to the separation device80to separate the carbon dioxide from the to-be-separated gas (such as the combustion exhaust gas). The carbon dioxide sublimators5A,5B are connected to the transmission side802of the permeable membrane803of the separation device80.

According to the above-mentioned carbon dioxide recovery devices100A,100B, the separation device80is provided with the permeable membrane (for example, an inorganic membrane such as a zeolite membrane and an organic membrane such as a molecular gate membrane)803to selectively transmit the carbon dioxide, and thus the carbon dioxide included in the to-be-separated gas (such as the combustion exhaust gas) that has been supplied to the separation device80is separated to the transmission side802of the permeable membrane803. Then, the carbon dioxide sublimators5A,5B are connected to the transmission side802of the permeable membrane803of the separation device80, and accordingly, the carbon dioxide separated from the to-be-separated gas is cooled by the refrigerant and sublimated (solidified) in the carbon dioxide sublimators5A,5B. The carbon dioxide sublimators5A,5B are depressurized by this sublimation (solidification) to depressurize the transmission side802of the separation device80connected with the carbon dioxide sublimators5A,5B, so that separation of the carbon dioxide by the permeable membrane803is promoted. A pump or the like for decompression is not required, and thus no electric power is necessary, achieving energy conservation. Further, this energy conservation can achieve suppression of increase in electric power cost and achieve suppression of generation of further carbon dioxide for power generation.

In the carbon dioxide recovery devices1A,1B,50A,50B,100A, and100B explained above, after the carbon dioxide is sublimated (solidified) to obtain dry ice, an inside temperature of the carbon dioxide sublimator5A (5B) is returned to a normal temperature to sublimate (gasify) the dry ice and the device recovers the dry ice from the take-out pipe54A (54B). As above, in recovering the carbon dioxide as gaseous body, for example, if a chemical plant is located adjacent to the carbon dioxide recovery devices1A,1B,50A,50B,100A, and100B, the carbon dioxide recovered as the gaseous body can be supplied to the chemical plant through a pipe, so that the carbon dioxide can be efficiently used.

Alternatively, in the carbon dioxide recovery devices1A,1B,50A,50B,100A, and100B, the carbon dioxide may be recovered as liquid body instead of gaseous body. In considering transportation after recovery of the carbon dioxide, it is better to recover as the liquid body since transportation by lorries or trucks is made more easily. Further, in the carbon dioxide sublimator5A (5B), liquefication of the dry ice rather than gasification can achieve a reduction in an increase range of a temperature inside the carbon dioxide sublimator5A (5B). Therefore, in order to sublimate (solidify) the carbon dioxide again after taking out the carbon dioxide from the carbon dioxide sublimator5A (5B), the cold heat used as the refrigerant for cooling the carbon dioxide sublimators5A,5B can be saved.

FIG.7is a graph showing a state of the carbon dioxide. According to this graph, a region surrounded by a melting line ML and a vaporization line VL is a region obtained by a liquid phase of the carbon dioxide (hereinafter, referred as liquefied carbon dioxide). Accordingly, in order to recover the liquefied carbon dioxide from the carbon dioxide sublimator5A (5B), the temperature of the dry ice needs to be increased at least to a triple point TP where the melting line ML, the vaporization line VL, and a sublimation line SL are crossed. However, before the temperature reaches the triple point TP, a certain amount of carbon dioxide gets gasified, and the thus gasified carbon dioxide cannot be liquefied depending on changes in the temperature under an isochoric state, resulting in loss of the carbon dioxide. To address this, the carbon dioxide sublimator5A (5B) is preferably controlled as mentioned below in order to make this loss as less as possible.

After performing sublimation (solidification) of the carbon dioxide in the carbon dioxide sublimators5A,5B, heat pumps52A,52B (one example of a heating medium) of the carbon dioxide sublimators5A,5B are set at a temperature of the triple point or higher of the carbon dioxide. Thereby, inside the carbon dioxide sublimators5A,5B that have been cooled for sublimating (solidifying) the carbon dioxide is heated to liquefy the carbon dioxide which is in a form of the dry ice.

Then, heating by the heat pumps52A,52B are halted at the time when the temperature of the obtained liquefied carbon dioxide is in a range of minus 56.6 degrees centigrade to minus 50 degrees centigrade inclusive so that the liquefied carbon dioxide is collected with less loss.

The applicant has confirmed from experiments that the liquefied carbon dioxide can be recovered with less loss when the temperature of the liquefied carbon dioxide is in the range of about minus 50 degrees centigrade to 10 degrees centigrade. However, once the temperature of the carbon dioxide has reached the triple point, there is a possibility that the temperature suddenly goes higher from the triple point, resulting in an increase in the loss In response to this, heating is stopped at the time when the temperature is in the range of minus 56.6 degrees centigrade to minus 50 degrees centigrade inclusive so that the temperature of the liquefied carbon dioxide can be in the above-mentioned range of about minus 50 degrees centigrade to 10 degrees centigrade.

The timing of stopping heating by the heat pumps52A.52B may be the time when a pressure inside the carbon dioxide sublimators5A,5B becomes 518 kPa or more and 800 kPa or less. This pressure range corresponds to a range in the graph ofFIG.7on the vaporization line VL in a range of minus 56.6 degrees centigrade to minus 50 degrees centigrade inclusive.

Further, it is preferable to start heating by the heat pumps52A,52B for recovering the liquefied carbon dioxide from the carbon dioxide sublimators5A,5B after the carbon dioxide is sublimated (solidified) until a ratio of a volume of the dry ice to a volume of the carbon dioxide sublimators5A,5B (hereinafter, referred simply as a volume ratio) is in a range of 0.1 to 0.3 inclusive. Thus, the liquefied carbon dioxide can be recovered with less loss.

FIG.8is a chart indicating a mass ratio of recoverable liquefied carbon dioxide and a mass ratio of gasified carbon dioxide (namely, a mass ratio of carbon dioxide that cannot be recovered and results in loss) with respect to a mass of the dry ice for each predetermined volume ratio in a case that the liquefied carbon dioxide is recovered under a condition (hereinafter, referred as a recovery condition) that the temperature of the liquefied carbon dioxide is minus 50 degrees centigrade and a pressure inside the carbon dioxide sublimators5A,5B is about 530 kPa.

For example, when the liquefied carbon dioxide is recovered under the above-mentioned recovery condition with a volume ratio of 0.12, the mass ratio of the recoverable liquefied carbon dioxide is 0.938 and the mass ratio of the gasified carbon dioxide is 0.062. Increase in the volume ratio from 0.12 causes increase in the mass ratio of the recoverable liquefied carbon dioxide, and accordingly, the loss is reduced. Then, when the liquefied carbon dioxide is recovered under the above recovery condition with the volume ratio of 0.3, the mass ratio of the recoverable liquefied carbon dioxide is 0.979 and the mass ratio of the gasified carbon dioxide is 0.021. In other words, after the carbon dioxide is sublimated (solidified) until the volume ratio is in the range of 0.1 to 0.3 inclusive, 90% or more than the mass of the dry ice can be recovered as the liquefied carbon dioxide as mentioned above.

Herein, the applicant has confirmed from experiments that the volume ratio less than 0.1 results in the mass ratio of the recoverable liquefied carbon dioxide as less than 0.9. The mass ratio less than 0.9 causes an increase in the loss by that amount, which is not preferable. Further, the applicant has confirmed from experiments that the volume ratio more than 0.3 results in a saturated state of the mass ratio of the recoverable liquefied carbon dioxide. If the carbon dioxide is to be sublimated (solidified) until the volume ratio becomes 0.3 or more, only the time required for sublimation (solidification) is increased while the mass ratio of the recoverable liquefied carbon dioxide is not increased, resulting in degradation in a recovery efficiency in the carbon dioxide, which is not preferable.

As mentioned above, in order to recover the liquefied carbon dioxide obtained in the carbon dioxide sublimators5A,5B, the open-close valves17A (17B) of the take-out pipe54A (54B) may be opened. Heating inside the carbon dioxide sublimators5A,5B causes increase in the pressure inside the carbon dioxide sublimators5A,5B, so that valve-opening of the open-close valves17A,17B leads to discharge of the liquefied carbon dioxide from the take-out pipe54A (54B) by push-out of the pressure inside the carbon dioxide sublimators5A,5B.

Fifth Embodiment

Further, when the liquefied carbon dioxide is to be recovered from the carbon dioxide sublimators5A,5B, like a carbon dioxide recovery device1C according to a fifth embodiment shown inFIG.9, for example, the carbon dioxide sublimators5A,5B may be connected with gas-liquid separators91A,91B, respectively. These gas-liquid separators91A,91B are, for example, devices configured to separate liquid and gas by use of a centrifugal force or surface tension and the like. The carbon dioxide recovery device1C shown inFIG.9has the same configuration as the carbon dioxide recovery device1A inFIG.1except the configuration that the gas-liquid separators91A,91B are connected to the carbon dioxide sublimators5A,5B. However, the configuration inFIG.9is only an example, and the gas-liquid separators91A,91B may be connected to the carbon dioxide sublimators5A,5B of any one of the carbon dioxide recovery devices1B,50A,50B,100A, and100B.

When a gaseous body such as nitrogen that remains in a gas state at minus 162 degrees centigrade (the temperature of the above-mentioned cold heat) flows into the carbon dioxide sublimators5A,5B (hereinafter, explanation is made with nitrogen as one example), nitrogen remains in the gas state even under the temperature and pressure condition for receiving the liquefied carbon dioxide from the carbon dioxide sublimators5A5B, so that the nitrogen could be discharged with the liquefied carbon dioxide when the liquefied carbon dioxide is to be output through the take-out pipe54A (54B) of the carbon dioxide sublimators5A,5B. To address this, the gas-liquid separators91A,91B are connected to the carbon dioxide sublimators5A,5B so that the liquefied carbon dioxide and the nitrogen flow into the gas-liquid separators91A,91B from the take-out pipe54A (54B), and thus the liquefied carbon dioxide and the nitrogen can be separated in the gas-liquid separators91A,91B.

To the gas-liquid separators91A,91B, gas discharge pipes94A,94B provided with open-close valves92A,92B are connected, and by opening the open-close valves92A,92B, the separated nitrogen can be discharged from the gas discharge pipes94A,94B. Further, to the gas-liquid separators91A,91B, liquefied-carbon-dioxide discharge pipes95A,95B provided with open-close valves93A,93B are connected, and by opening the open-close valves93A,93B, the liquefied carbon dioxide that has been separated from the nitrogen can be taken out from the liquefied-carbon-dioxide discharge pipes95A,95B.

Sixth Embodiment

Furthermore, when carbon dioxide is to be recovered in a form of liquid, the carbon dioxide sublimators5A,5B may be connected with solid-liquid separators96A,96B as a carbon dioxide recovery device1D according to a sixth embodiment shown inFIG.10. These solid-liquid separators96A, % B are, for example, devices configured to separate liquid and solid by use of a sedimentation method, a centrifugation method, a compression method, a filtration method, and others. Herein, the carbon dioxide recovery device1D shown inFIG.10has the same configuration as the carbon dioxide recovery device1A shown inFIG.1except the configuration that the carbon dioxide sublimators5A,5B are connected with the solid-liquid separators96A,96B, respectively. However, the configuration shown inFIG.10is only one illustration, and the solid-liquid separators96A,96B may be connected to the carbon dioxide sublimators5A,5B of the respective carbon dioxide recovery devices1B,50A,50B,100A, and100B.

When moisture is mixed in the carbon dioxide sublimators5A,5B in a process of obtaining liquefied carbon dioxide from dry ice, the moisture is solidified to turn ice depending on a temperature condition in recovering the liquefied carbon dioxide from the carbon dioxide sublimators5A,5B. This ice could be discharged with the liquefied carbon dioxide when the liquefied carbon dioxide is to be output from the take-out pipe54A (54B) of the carbon dioxide sublimators5A,5B. To address this, the solid-liquid separators96A,96B are connected to the carbon dioxide sublimators5A,5B, respectively, such that the liquefied carbon dioxide and the ice flow into the solid-liquid separators96A,96B from the take-out pipe54A (54B), and thereby the liquefied carbon dioxide and the ice can be separated in the solid-liquid separators96A, % B.

The solid-liquid separators % A,96B are connected with liquefied-carbon-dioxide discharge pipes98A,98B provided with open-close valves97A,97B, respectively, and the liquefied carbon dioxide that has been separated from the ice can be taken out from the liquefied-carbon-dioxide discharge pipes98A,98B by opening the open-close valves97A,97B.

Further, the above explanation has been made with a situation where the carbon dioxide sublimators5A,5B are connected with either the gas-liquid separators91A,91B or the solid-liquid separators96A,96B, but the carbon dioxide sublimators5A,5B may be connected with the gas-liquid separators91A,91B and the solid-liquid separators96A,96B in this order in series.

Configuration of Carbon Dioxide Sublimator

The carbon dioxide sublimators5A,5B used for the above-mentioned carbon dioxide recovery devices1A,1B,1C,1D,50A,50B,100A, and100B may have a configuration as shown inFIG.13andFIG.14. InFIG.13,FIG.14, and the following explanation, indication of the carbon dioxide sublimator is simply made as the carbon dioxide sublimator5.

The carbon dioxide sublimator5is configured by coupling a sublimation chamber55for sublimating (solidifying) carbon dioxide and a recovery chamber56for recovering a dry ice90as the sublimated (solidified) carbon dioxide.

The sublimation chamber55is connected with a transfer pipe L21to introduce the carbon dioxide to inside the sublimation chamber55from the transfer pipe L21. Herein, this transfer pipe L21corresponds to any one of the second transfer pipes L16A, L16B in the carbon dioxide recovery device1A (seeFIG.1), the branch transfer pipes L161A, L161B in the carbon dioxide recovery device1B (seeFIG.2), the transfer pipes L15A, L15B in the carbon dioxide recovery device50A (seeFIG.3), the second transfer pipes L16A, L16B in the carbon dioxide recovery device50B (seeFIG.4), the branch transfer pipes L151A, L151B in the carbon dioxide recovery device100A (seeFIG.5), the second transfer pipes L16A, L16B in the carbon dioxide recovery device100B (seeFIG.6), the second transfer pipes L16A, L16B in the carbon dioxide recovery device1C (seeFIG.9), and the second transfer pipes L16A, L16B in the carbon dioxide recovery device1D (seeFIG.10).

The sublimation chamber55is arranged inside with a heat exchanger51connected to a refrigerant circuit12. Thus, inside the sublimation chamber55can be cooled down to a temperature appropriate for sublimation (solidification) of the carbon dioxide. Herein, the temperature appropriate for sublimation (solidification) of the carbon dioxide is, as mentioned above, about minus 85 degrees centigrade or below when the combustion exhaust gas from an iron manufacturing plant or a cement plant is used as the to-be-separated gas, about minus 96 degrees centigrade or below when the combustion exhaust gas from the power plant is used as the to-be-separated gas, and about minus 140 degrees centigrade or below when the atmosphere is used as the to-be-separated gas. Further, an outer circumferential surface of the heat exchanger51is an attachment surface57(one example of an attachment portion) to which the dry ice90sublimated (solidified) in the sublimation chamber55is to be attached.

Further, the attachment surface57is connected with a heater58. This heater58is for example, a cartridge heater. Operation of the heater58allows local heating of the attachment surface57of the heat exchanger51. By heating the attachment surface57, a surface contacted with the attachment surface57of the dry ice90which is attached to the attachment surface57can be sublimated (gasified). Thus, the dry ice90can be fallen off from the attachment surface57.

The sublimation chamber55is provided with a first opening port552on an end portion on a side of the recovery chamber56. Further, the sublimation chamber55is provided with a slant portion551constituting a downward slope toward the first opening port552between the heat exchanger51and the first opening port552.

The recovery chamber56is provided with a second opening port561on an end portion on a side of the sublimation chamber55. Then, the first opening port552of the sublimation chamber55and the second opening port561of the recovery chamber56are connected via a shut-off member59. When the shut-off member59is brought in a closed state, inside the sublimation chamber55and inside the recovery chamber56are blocked (FIG.13), and when the shut-off member59is brought in an open state, inside the sublimation chamber55and inside the recovery chamber56are in a communicated state (FIG.14). The recovery chamber56is located below the attachment surface57, so that once inside the sublimation chamber55and inside the recovery chamber56are communicated, the recovery chamber56can receive the dry ice90which is falling off the attachment surface57. Further, the recovery chamber56is connected with a take-out pipe54. This take-out pipe54is identical with the above-mentioned take-out pipe54A (54B).

When the carbon dioxide sublimator5having the above-mentioned configuration is used, recovery of the carbon dioxide is performed as below.

Firstly, inside the sublimation chamber55is cooled by the heat exchanger51(the refrigerant flowing in the refrigerant circuit12) to a temperature appropriate for sublimation (solidification) of the carbon dioxide. At this time, the shut-off member59is made to be in the closed state. While inside the sublimation chamber55is being cooled down, the carbon dioxide is introduced in the sublimation chamber55from the transfer pipe L21. The carbon dioxide introduced in the sublimation chamber55is sublimated (solidified) to be attached to the attachment surface57as shown inFIG.13.

The heater58is operated while the dry ice90remains attached to the attachment surface57, and thus the attachment surface57is heated to sublimate (gasify) the surface of the dry ice90to which the attachment surface57is attached. By this sublimation (gasification), the dry ice90attached to the attachment surface57is fallen off toward the slant portion551as indicated with an arrow A11inFIG.14by the gravity. Then, the dry ice90having fallen to the slant portion551slides on the slant portion551toward the first opening port552as indicated with an arrow A12by gravity. At this time, the shut-off member59is in the open state so that the dry ice90passes through the second opening port561from the first opening port552and then accommodated in the recovery chamber56. The dry ice90accommodated in the recovery chamber56is sublimated (gasified) or liquefied and recovered from the take-out pipe54. Herein, a casing of the recovery chamber56may be provided with a door or the like which is accessible to inside the recovery chamber56so that the carbon dioxide is recovered through that door in a form of solid.

Sublimation (gasification) of a contact surface of the dry ice90with the attachment surface57is enough for making the dry ice90fall from the attachment surface57, and thus heating of the heater58may be made in a short time. Accordingly, the temperature of the sublimation chamber55that has been cooled to the temperature appropriate for sublimation (solidification) of the carbon dioxide does not have to be increased until the dry ice90is gasified or liquefied. In other words, a temperature changing range of the sublimation chamber55in recovering the dry ice90can be made small, and thus it is possible to suppress thermal impact applying to the sublimation chamber55. Further, the thus small temperature changing range achieves suppression in loss of the cold heat and time which are required for cooling the sublimation chamber55in performing sublimation (solidification) of the carbon dioxide again in the sublimation chamber55after recovering the dry ice90.

Herein, in each of the above-mentioned carbon dioxide recovery devices1A,1B,1C,1D,50A,50B,100A, and100B, the two carbon dioxide sublimators5A,5B are used (seeFIG.1.FIG.2,FIG.3,FIG.4,FIG.5,FIG.6,FIG.9, andFIG.10). This is because while the one carbon dioxide sublimator5A or5B recovers the carbon dioxide that has been completed with sublimation (solidification), the other carbon dioxide sublimator5A or5B is made to perform sublimation (solidification) of the carbon dioxide, and thereby, recovery efficiency of the carbon dioxide can be improved.

However, if the carbon dioxide sublimator5shown inFIG.13andFIG.14is to be used, two sublimators do not necessarily have to be provided. As mentioned above, the carbon dioxide sublimator5can reduce the temperature changing range of the sublimation chamber55in recovering the dry ice90, so that the subsequent sublimation (solidification) can be performed in a short time after the dry ice90is made to fall off the attachment surface57, and thus the carbon dioxide can be efficiently recovered without using two sublimators.

The above-mentioned carbon dioxide recovery devices1A,1B,1C,1D,50A,50B,100A, and100B are only illustrations and have no any limitation to the present invention. Accordingly, the present invention can naturally be made with any improvements or modifications without departing from scope of the invention. For example, the features that the temperature of the water vapor condenser4A (4B) is set to 1 degree centigrade, the carbon dioxide sublimator5A (5B) is set at a temperature appropriate for sublimation (solidification) of the carbon dioxide, and the pressure of the separation device70A (70B) is decompressed to about 4 kPa are only illustrations and the invention is not limited to those. For example, the temperature of the carbon dioxide sublimator5A (5B) may be lower so that the carbon dioxide is made to turn dry ice more rapidly. However, if the temperature is lowered too much, there is contrarily a possibility of degradation in the recovery efficiency of the carbon dioxide since it is considered that when the carbon dioxide is to be recovered from the carbon dioxide sublimator5A (5B), sublimation (gasification) of the dry ice takes time and the pressure of the regeneration tower3becomes too low, so that the adsorbent is in a coexistence state of liquid and solid, resulting in degradation in efficiency of diffusing the carbon dioxide. Accordingly, the temperature of the carbon dioxide sublimator5A (5B) is appropriately adjusted in accordance with the recovery efficiency of the carbon dioxide.

REFERENCE SIGNS LIST