Description HIGH PRESSURE CARBON DIOXIDE FINE-BUBBLE GENERATING APPARATUS AND CARBON DIOXIDE UNDERGROUND STORAGE SYSTEM MAKING USE OF THE APPARATUS Technical Field [0001] The present invention relates to a high pressure carbon dioxide fine-bubble generating apparatus used to achieve an improvement in dissolution efficiency when carbon dioxide captured from a large scale discharge source of carbon dioxide, or the like is dissolved in a solvent composed of seawater and/or water to be injected into a ground in order to contribute to reduction of carbon dioxide, which is one of greenhouse effect gases responsible for global warming, and a carbon dioxide underground storage system making use of the apparatus to store carbon dioxide stably over a long term. Background Art [0002] Conventionally, it has been tried to compress carbon dioxide, which is captured from exhausted gases, in a liquid or supercritical condition to inject the same under pressure into a ground from an injection well as described in the 1 following non-Patent Documents 1 and 2 when the carbon dioxide is to be stored in an exhausted petroleum field or gas field in the ground, or in an aquifer. Generally, the carbon dioxide is injected under pressure into a storage layer having a depth of 800 meters or more to maintain a supercritical condition of carbon dioxide (temperature of 31 *C or higher and pressure of 7.4 MPa or more in case of carbon dioxide) to make carbon dioxide large in density to accomplish an efficient storage. [00031 Since carbon dioxide put in a supercritical condition is smaller in specific gravity than a peripheral underground water and moves upward due to buoyancy, however, it is required that a seal layer (cap lock) being dome-shaped to trap carbon dioxide floating centrally of an upper portion thereof be formed as an aquifer for storage of carbon dioxide. Incidentally, while it is generally confirmed that a storage layer in a petroleum field or a gas field has a trap structure having a combination of the seal layer and the dome shape, it is a task to find an aquifer, which is conformed to such conditions, in the nature. Therefore, there has been desired a method that enlarges applicable conditions and does not permit carbon dioxide to float but stores the carbon dioxide in the ground stably over a long term. [0004] On the other hand, methods of injecting carbon dioxide 2 under pressure into a ground include one, which is described in the following Patent Document 1 and in which carbon dioxide increased in pressure by a C02 booster and water increased in pressure by a pump are injected under pressure from above a pipe extending into a ground from an earth surface while flowing and mixing together, one, which is described in the following Patent Document 2 and in which carbon dioxide is stored in an underground layer of a petroleum field or a gas field while being put in a state of being dissolved in water by a mixer, one, which is described in the following Patent Document 3 and in which gases containing carbon dioxide are made micro-bubbles to be dispersed in water or seawater and the carbon dioxide being made micro-bubbles is isolated in a deep underground. All the methods comprise injecting a solvent of seawater or water and carbon dioxide under pressure into an aquifer to dissolve the carbon dioxide in the solvent to store the same. [0005] With the methods described in the Patent Documents 1 to 3, however, carbon dioxide is dissolved at a high concentration of a saturated concentration level into a solvent to bring about a state of being made larger in specific gravity than a peripheral underground water to store carbon dioxide into an aquifer stably over a long term, but a dissolved level of carbon dioxide is thought to be insufficient according to conditions 3 of dissolution to cause a fear that it is not possible to bring about a state of being made larger in specific gravity than a peripheral underground water, in the case where the solvent comprises only water and means of dissolution comprises "confluence", "mixer", and "micro-bubble generator". [0006) Hereupon, the applicant of the present application has proposed, in the following Patent Document 4, a carbon dioxide underground storage system comprising a carbon dioxide compressor that compresses carbon dioxide to a liquid or supercritical condition, a pressure feeding pump that performs compression-delivery of a solvent composed of seawater and/or water, one or more dissolving tanks that permit injection of the compressed carbon dioxide and the solvent thereinto to permit the solvent to dissolve the carbon dioxide to make carbon dioxide dissolved water, and an injection well extending from the ground surface to the aquifer to have the resultant carbon dioxide dissolved water injected under pressure into the underground aquifer, and wherein the dissolving tanks comprise a closed container provided on a lower portion thereof with a carbon dioxide injection port, into which carbon dioxide fed from the carbon dioxide compressor is injected, and a solvent injection port, into which a solvent fed from the solvent pressure feeding pump is injected, and the container is formed on an upper portion thereof with a discharge port, from which 4 the carbon dioxide dissolved water is discharged, and filled with a granular filler. Non-Patent Document 1: IPCC, "IPCC Special Report on Carbon Dioxide Capture and Storage", Chapter 5, 2005, Cambridge University Press Non-Patent Document 2: Shinichi Ozeki, Yasuji Kano, "Looking forward to Petroleum Natural Gas Upstream Technology toward realization of "Carbon Dioxide Underground Storage" Project", "Petroleum Natural Gas Review", Independent Administrative Corporation, Petroleum Natural Gas Metallic Mineral Resource Organization, 2006.7, Vol. 40, No. 4, pages 57-70 Patent Document 1: JP-A-6-170215 Patent Document 2: JP-A-3-258340 Patent Document 3: JP-A-2004-50167 Patent Document 4: Japanese Patent Application No. 2007-82078 Disclosure of the Invention Problems that the Invention is to Solve [0007] However, the dissolving tank in the Patent Document 4 involves a problem that the dissolving tank is increased in volume in order to promote sufficient dissolution of carbon dioxide and to process a large quantity of carbon dioxide efficiently and a problem that the dissolving tank is increased in flow passage length, that is, height dimension in order to 5 ensure retention time in the dissolving tank. [0008] In order to solve such problem, the inventors of the present application have carried out studies earnestly to obtain knowledge that it is effective to generate fine-bubble carbon dioxide to achieve an increase in contact area with a solvent. While, for example, the micro-bubble generator described above has been developed as a fine-bubble generating apparatus, some micro-bubble generators, which involve release of internal and external pressures, cannot be adopted in principle since dissolution of carbon dioxide is performed under a high pressure condition of at least 8 MPa (8 to 20 MPa). Also, ejector systems and revolving current systems are not examined under a high pressure condition and include mechanisms being too complex to be applied to a high pressure condition, thus involving a problem of deficiency in reliability and durability. [0009] Hereupon, firstly, it is a main object of the invention to provide a high pressure carbon dioxide fine-bubble generating apparatus having an efficient and high processing capacity of generating fine-bubble and mixing carbon dioxide into a solvent under a high pressure condition. [0010] Also, secondly, it is an object to provide a carbon 6 dioxide underground storage system, by which a carbon dioxide dissolved water is injected under pressure into an aquifer to be stored in a state, in which carbon dioxide is dissolved at a high concentration around a saturated concentration level into a solvent (seawater or water), by the use of the high pressure carbon dioxide fine-bubble generating apparatus. Means for Solving the Problem [0011] In order to solve such problem, the invention according to claim 1 provides a high pressure carbon dioxide fine-bubble generating apparatus that generates fine-bubble and mixes carbon dioxide, which is compressed to a liquid or supercritical condition, into a solvent, high pressure carbon dioxide fine-bubble generating apparatus characterized in that a supply pipeline of the carbon dioxide is arranged in a main pipeline, through which the solvent is caused to flow at a predetermined, high flow velocity, or a supply pipeline of the carbon dioxide is arranged to be fitted externally onto the main pipeline, small holes are formed on a pipeline wall surface, which partitions the solvent and carbon dioxide, and a shearing force of a solvent flowing through the main pipeline mixes the carbon dioxide while fine-bubble generating the same. [0012] 7 With the invention according to claim 1, a shearing force of a solvent flowing through the main pipeline mixes the carbon dioxide while fine-bubble generating the same. With such construction, it is possible to generate fine-bubble and mix carbon dioxide into a solvent efficiently in a state, in which a high pressure condition is maintained, with a high processing capacity without being accompanied by pressure release. Also, since the construction is composed of a combination of pipelines, it can be incorporated simply into a pipeline. [0013) Provided as the invention according to claim 2 is the high pressure carbon dioxide fine-bubble generating apparatus according to claim 1, wherein a flow velocity of the solvent and a diameter of the small holes are set so that the Weber number (We) found by the following formula (1) is made at least 10. [Formula 1] We = (p.V 2 d)/a (1) where pw: water density (kg/m 3 ), V: water flow velocity in a pipeline (m/s), d: diameter of the small holes (m), and a: interfacial tension (N/m). By making the Weber number (We) at least 10 according to later-described Embodiment 2-3 in setting a flow velocity of the solvent and a diameter of the small holes, the invention according to claim 2 enables fine-bubble generation 8 efficiently with a high processing capacity to present a high dissolution efficiency. [0014] In order to solve the second problem described above, the invention according to claim 3 provides a carbon dioxide underground storage system, by which carbon dioxide in a state of being dissolved into a solvent is injected under pressure into an aquifer to be stored, the carbon dioxide underground storage system comprising a carbon dioxide compressor that compresses carbon dioxide to a liquid or supercritical condition, and a pressure feeding pump that performs compression- delivery of a solvent composed of seawater and/or water, and mounts a high pressure carbon dioxide fine-bubble generating apparatus including in that a supply pipeline of the carbon dioxide is arranged in amain pipeline, through which the solvent is caused to flow at a predetermined, high flow velocity, or a supply pipeline of the carbon dioxide is arranged to be fitted externally onto the main pipeline, small holes are formed on a pipeline wall surface, which partitions the solvent and carbon dioxide, and a shearing force of a solvent flowing through the main pipeline mixes the carbon dioxide while fine-bubble generating the same, and wherein one or more dissolving tanks are mounted subsequent to the high pressure carbon dioxide fine-bubble generating apparatus to comprise a closed container provided on a lower portion thereof with 9 a solvent injection port, into which the carbon dioxide as generated fine-bubble is injected, the container being formed on an upper portion thereof with a discharge port, from which the carbon dioxide dissolved water is discharged, and filled with a granular filler, and an injection well extending from the ground surface to the aquifer is mounted to have the carbon dioxide dissolved water, which is discharged from the dissolving tank or tanks, injected under pressure into the underground aquifer. [0015] With the invention according to claim 3, firstly, the dissolving tank or tanks are constructed with a granular filler filled in a closed container, whereby it is possible in the dissolving tank or tanks to dissolve carbon dioxide (a liquid or supercritical condition) at a high concentration around a saturated concentration level into a solvent (seawater or water), so that a carbon dioxide dissolved water becomes larger in specific gravity than the peripheral, underground water, thus enabling storing carbon dioxide stably over a long term. [0016] Also, a high pressure carbon dioxide fine-bubble generating apparatus is mounted preceding the dissolving tank or tanks whereby it is possible as shown in later-described Embodiment 2-1 to realize high dissolution efficiency by virtue of a synergetic effect with the dissolving tank or tanks. 10 Consequently, the dissolving tank or tanks can be made compact and a high processing capacity is provided. [0017] The invention according to claim 4 provides the carbon dioxide underground storage system according to claim 3, wherein a separator tank that separates the whole quantity of a carbon dioxide dissolved water as fed into a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state, in which carbon dioxide is dissolved in solubility, and a carbon dioxide pressure feeder that returns the non-dissolved carbon dioxide as separated to an intermediate flow passage between the carbon dioxide compressor and the dissolving tank are provided in the course of a flow passage extending to the injection well from the dissolving tank. [0018] With the invention according to claim 4, non-dissolved carbon dioxide is separated from the whole quantity of a carbon dioxide dissolved water, which is created in the dissolving tank or tanks, in the separator tank, and the non-dissolved carbon dioxide is returned to the dissolving tank or tanks, whereby carbon dioxide in a state of being dissolved into a solvent (seawater or water) can be surely injected under pressure at a saturated concentration level into the underground. The carbon dioxide dissolved water will become larger in specific gravity than the peripheral, underground 11 water in then aquifer and is even injected into the aquifer to cause carbon dioxide not to float, thus enabling storing carbon dioxide in the aquifer stably over a long term. [0019] In order to solve the second problem described above, the second invention according to claim 5 provides a carbon dioxide underground storage system, by which carbon dioxide in a state of being dissolved into a solvent is injected under pressure into an underground aquifer to be stored, the carbon dioxide underground storage system comprising a carbon dioxide compressor that compresses carbon dioxide to a liquid or supercritical condition, a pressure feeding pump that performs compression- delivery of a solvent composed of seawater and/or water, one or more dissolving tanks that permit injection of the compressed carbon dioxide and the solvent thereinto to permit the solvent to dissolve the carbon dioxide to make carbon dioxide dissolved water, and an injection well extending from the ground surface to the aquifer to have the resultant carbon dioxide dissolved water injected under pressure into the underground aquifer, and wherein the dissolving tanks comprise a closed container provided on a lower portion thereof with a carbon dioxide injection port, into which carbon dioxide fed from the carbon dioxide compressor is injected, and a solvent injection port, into which a solvent fed from the solvent pressure feeding pump 12 is injected, the container being formed on an upper portion thereof with a discharge port, from which the carbon dioxide dissolved water is discharged, and filled with a granular filler, a separator tank that separates the whole quantity of a carbon dioxide dissolved water as fed into a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state, in which carbon dioxide is dissolved in solubility, anda carbon dioxide pressure feeder that feeds the carbon dioxide as separated in the separator tank under pressure are provided in the course of a flow passage extending to the injection well from the dissolving tank, a high pressure carbon dioxide fine-bubble generating apparatus is mounted subsequently to the carbon dioxide pressure feeder such that a carbon dioxide supply pipeline, to which the carbon dioxide fed under pressure from the carbon dioxide pressure feeder is fed, or a carbon dioxide supply pipeline, which is fitted externally onto the main pipeline and to which the carbon dioxide fed under pressure from the carbon dioxide pressure feeder is fed, is arranged in the main pipeline, through which the carbon dioxide dissolved water is caused to flow at a predetermined, high flow velocity, small holes are formed on a pipeline wall surface, which partitions the carbon dioxide dissolved water and carbon dioxide, and the carbon dioxide is mixed while being generated fine-bubble by a shearing force of the carbon dioxide dissolved 13 water flowing through the main pipeline. [0020] The invention according to claim 5 shows a configuration, in which the high pressure carbon dioxide fine-bubble generating apparatus is incorporated into a pipeline extending to the injection well from the dissolving tank. [0021] The invention according to claim 6 provides the carbon dioxide underground storage system according to claim 5, wherein a branch device is arranged between the carbon dioxide pressure feeder and the supply pipeline to branch carbon dioxide fed under pressure from the carbon dioxide pressure feeder, the branch device branches that quantity of the carbon dioxide, which can be dissolved in a path extending from the fine-bubble generating apparatus to the aquifer, to feed the same under pressure to the supply pipeline, and the remainder of the carbon dioxide is returned to the dissolving tank or tanks. [0022] With the invention according to claim 6, a non-dissolved carbon dioxide is returned to the dissolving tank or tanks whereby carbon dioxide in a state of being dissolved into a solvent (seawater or water) can be surely injected under pressure at a saturated concentration level into the underground. 14 [0023] The invention according to claim 7 provides the carbon dioxide underground storage system according to any one of claims 3 to 6, wherein the granular filler filled in the dissolving tank or tanks is composed of any one of, or a combination of sand, crushed stone, Raschig ring, and saddle. [0024] With the invention according to claim 7, any one of, or a combination of sand, crushed stone, Raschig ring, and saddle is used as a granular filler filled in the dissolving tanks. [0025] The invention according to claim 8 provides the carbon dioxide underground storage system according to any one of claims 3 to 7, wherein the granular filler filled in the dissolving tank or tanks has an optimum, average particle size, which is determined by a quantity of dissolved carbon dioxide determined by flow rates of carbon dioxide and a solvent and the shape of dissolving tanks and a pressure loss in the dissolving tanks, every kind of a filler. [0026] With the invention according to claim 8, used as the granular filler is one having an optimum, average particle size, which is determined by a quantity of dissolved carbon dioxide determined by flow rates of carbon dioxide and a solvent and the shape of the dissolving tanks and a pressure loss in the 15 dissolving tanks, every kind of a filler, so that an average particle size amounting to the optimum, average particle size is excellent in efficiency of dissolution. [0027] The invention according to claim 9 provides the carbon dioxide underground storage system according to any one of claims 3 to 8, wherein one or plural rectifying plates, on which a multiplicity of openings are formed so as to partition a flow passage, are provided in the filled region of the filler. With the invention according to claim 9, the rectifying plates are provided to thereby promote dissolution of carbon dioxide in the dissolving tanks. Effect of the Invention [0028] As described above in detail, with the high pressure carbon dioxide fine-bubble generating apparatus according to the invention, it is possible to generate fine-bubble and mix carbon dioxide into a solvent efficiently under a high pressure condition with a high processing capacity. [0029] Also, with the carbon dioxide underground storage system according to the invention, it is possible to inject a carbon dioxide dissolved water under pressure into an aquifer in a state, in which carbon dioxide is dissolved at a high 16 concentration around a saturated concentration level into a solvent (seawater or water), to store carbon dioxide. Best Mode for Carrying Out the Invention [0030] Embodiments of the invention will be described below with reference to the drawings. A detailed explanation will be given in the order of a high pressure carbon dioxide fine-bubble generating apparatus 7 and a carbon dioxide storage system 1 making use of the apparatus. [0031] [high pressure carbon dioxide fine-bubble generating apparatus 7] The high pressure carbon dioxide fine-bubble generating apparatus 7 (referred below simply to as fine-bubble generating apparatus) will be described in detail with reference to Figs. 1 to 3. The fine-bubble generating apparatus 7 generates fine-bubble carbon dioxide, which is compressed to a liquid or supercritical condition, to mix the same in a solvent to thereby promote dissolution of carbon dioxide owing to an increase in contact area. The fine-bubble generating apparatus 7 is used singly, or preferably used in combination with dissolving tanks 4 as in an embodiment described later. [0032] 17 (First embodiment) A fine-bubble generating apparatus 7A according to a first embodiment shown in Fig. 1 makes use of seawater and/or water as a solvent in the case of a first component pattern of two carbon dioxide underground storage systems described later and makes use of a carbon dioxide dissolved water as a solvent as a solvent in the case of a second component pattern, a carbon dioxide supply pipeline 31 being arranged to be fitted externally onto a main pipeline 30, through which the solvent is caused to flow at a predetermined, high flow velocity, small holes 30a, 30a, ... being formed on a pipeline wall surface, which partitions the solvent and carbon dioxide, or a pipeline wall surface of the main pipeline 30 in the case of an example shown in the figure, and a shearing force of the solvent flowing through the main pipeline 30 acting to generate fine-bubble carbon dioxide, which is compressed to a liquid or supercritical condition, to mix the same therein. [0033] It is desired that when being provided in plural, the small holes 30a be arranged circumferentially evenly on the pipeline wall surface of the main pipeline 30 and at intervals in multi-stages in an axial direction as shown in the figure. [0034] It is desired that the velocity of flow of the solvent and a diameter of the small holes 30a be set so that Weber's 18 number (We) found by the following formula (1) amounts to 10 or more according to Embodiment 2-3 described later. However, this is on condition that the velocity of flow of carbon dioxide from the small holes is at least 8x10- 2 m/s. [Formula 1] We = (pwV 2 d)/a (i) Here, pw: water density (kg/m 3 ), V: water flow velocity in a pipeline (m/s), d: diameter of the small holes (m), and a: interfacial tension (N/m). [0035] In addition, the generated fine-bubble carbon dioxide is sufficient to have substantially a diameter of 0.05 to 0.2 mm and it is unnecessary to generate fine-bubble carbon dioxide especially to micro-level (10 to several tens pm). [0036] (Second embodiment) With fine-bubble generating apparatus 7B, 7C according to a second embodiment shown in Figs. 2 and 3, a carbon dioxide supply pipeline 31 is arranged in a main pipeline 30, through which a solvent is caused to flow at a predetermined, high flow velocity, small holes 31a, 31a, ... are formed on a pipeline wall surface, which partitions the solvent and carbon dioxide, or a pipeline wall surface of the carbon dioxide supply pipeline 31 in the case of an example shown in the figure, and a shearing force of the solvent flowing through the main pipeline 30 acts 19 to generate fine-bubble carbon dioxide, which is compressed to a liquid or supercritical condition, to mix the same therein. [0037] [carbon dioxide underground storage system 11 A carbon dioxide underground storage system lA shown in Fig. 4 traps carbon dioxide, which is captured from a large scale discharge source of carbon dioxide, or the like, into the underground aquifer in a state, in which carbon dioxide is dissolved at a high concentration around a saturated concentration level into a solvent (seawater or water), to store the same stably over a long term. [0038] Since carbon dioxide is dissolved into a solvent at a high concentration of a saturated concentration level to bring about a state of being made larger in specific gravity than a peripheral underground water to store carbon dioxide in the aquifer stably over a long term, a target quantity of dissolution of carbon dioxide is 40 to 50 kg, preferably 45 to 50 kg per 1 m 3 of a solvent. [0039] Also, pressure in the system is maintained in a state of high pressure of at least 8 MPa so as to cause dissolution in a state, in which carbon dioxide is maintained in a liquid or supercritical condition, and taking into consideration pressure, at which a carbon dioxide dissolved water is injected 20 under pressure into the underground aquifer, and a pressure loss in a piping system. [0040] [First component pattern] As shown in Fig. 4, the underground storage system 1A comprises a carbon dioxide compressor 2 that compresses carbon dioxide to a liquid or supercritical condition, a pressure feeding pump 3 for compression- delivery of a solvent composed of seawater and/or water, fine-bubble generating apparatus 7, 7, ... that generate fine-bubble carbon dioxide, which is compressed to the liquid or supercritical condition, to mix the same into a solvent, a plurality of dissolving tanks 4, 4, ... that allow injection of a solvent, into which the carbon dioxide generated fine-bubble by the fine-bubble generating apparatus 7, 7, ... is mixed, and dissolution of the carbon dioxide into the solvent to make a carbon dioxide dissolved water, andan injectionwell 5 extending fromthe ground surface to the aquifer to allow the resultant carbon dioxide dissolved water to be injected under pressure into the underground aquifer. In addition, according to the embodiment, the dissolving tanks 4 are mounted in plural to promote dissolution of carbon dioxide but suffice to be provided in any number conformed to a processing capacity. [0041] As shown in Fig. 5, the fine-bubble generating apparatus 21 7 use the fine-bubble generating apparatus 7, according to the second embodiment, in which the carbon dioxide supply pipeline 31 is arranged in the main pipeline 30, which is mounted below each of the dissolving tanks 4 and through which a solvent is caused to flow at a predetermined, high flow velocity, the small holes 31a, 31a, ... are formed on that pipeline wall surface of the carbon dioxide supply pipeline 31, which partitions the solvent and carbon dioxide, and a shearing force of the solvent flowing through the main pipeline 30 acts to generate fine-bubble carbon dioxide, which is compressed to a liquid or supercritical condition, to mix the same therein. [0042] As shown in Fig. 5, the dissolving tanks 4 are constructed such that an injection port 9, into which a solvent mixed with the carbon dioxide generated fine-bubble by the fine-bubble generating apparatus 7 is injected, is formed on a lower portion of a closed vessel 10, a discharge port 13, through which the carbon dioxide dissolved water is discharged, is formed on an upper portion of the vessel 10, perforated plates 14, 14 are arranged on the upper and lower portions of the vessel 10 to compartment an interior of the vessel 10 vertically, and a granular filler 16 is filled between the perforated plates 14, 14. Also, a mesh plate 15 is mounted at the injection port 9. [0043] 22 The filler 16 serves to promote agitation of a solvent and carbon dioxide to make dissolution of carbon dioxide efficient, and can be composed of, for example, any one of, or a combination of sand, crushed stone, Raschig ring, and saddle. The Raschig ring comprises a cylindrical-shaped filler used in a packed tower and composed of ceramic, plastic, metal, carbon, etc. and can adopt generally widely used ones. The saddle is filler, which is used in a packed tower and formed from ceramic, saddle-shaped, and is generally formed to be made smaller in pressure loss than the Raschig ring. [0044] Also, the filler 16 preferably has an optimum, average particle size, which is determined by a quantity of dissolved carbon dioxide determined by flow rates of carbon dioxide and a solvent and the shape of the dissolving tanks and a pressure loss in the dissolving tanks, every kind of a filler. Specifically, after the two following relationships (1) and (2) for an average particle size of a filler are obtained experimentarily, an average particle size, which makes a quantity of dissolution largest for an allowable pressure loss (a pressure difference between an injection port and a discharge port of a dissolving tank) in a dissolving tank, is selected as an optimum, average particle size every kind of a filler. (1) The relationship between an average particle size of 23 filler and a quantity of dissolved carbon dioxide for predetermined flow rates of carbon dioxide and a solvent and the shape of a dissolving tank. (2) The relationship between an average particle size of filler and a pressure loss of a dissolving tank. [0045] Generally, the characteristics for the average particle size of a filler is such that (1) given flow rates of carbon dioxide and a solvent and the shape of a dissolving tank, the smaller an average particle size of a filler, the larger the quantity of dissolved carbon dioxide. (2) On the other hand, there is a tendency that the smaller an average particle size of a filler, the larger a pressure loss due to flow of carbon dioxide and a solvent in a dissolving tank, and so energy used for ensuring a predetermined flow rate increases. Accordingly, an average particle size of filler should be selected taking comprehensive account of the flow rates of carbon dioxide and a solvent and the shape of a dissolving tank. A filler 16 having the optimum, average particle size is used to lead to an excellent dissolution efficiency of carbon dioxide. [0046] As shown in Fig. 5, the vessel 10 is preferably in the form of a pipe being longitudinal and closed. Thereby, it becomes possible to ensure time, during which carbon dioxide and a solvent are retained in the dissolving tanks 4. Also, 24 it is possible to form a construction having a pressure tightness for the set pressure in the system and to create carbon dioxide dissolved water continuously and stably in a short period of time. (0047] Here, in explaining flow in the dissolving tanks 4, carbon dioxide and a solvent, which are fed under pressure into the vessel 10 from the injection port 9, enter a region, in which the filler 16 is filled, evenly from the mesh plate 15. In the region, in which the filler 16 is filled, a solvent and carbon dioxide are adequately agitated in keeping with flow between the filler 16, so that carbon dioxide is dissolved into the solvent to flow upward. When this action accomplishes arrival to the upper, perforated plate 14, carbon dioxide dissolved water with carbon dioxide substantially dissolved into the solvent is created to reach a saturated dissolved level of the solvent. Thereafter, the carbon dioxide dissolved water having entered an upper hopper portion 18 from the upper, perforated plate 14 is discharged from the discharge port 13. [0048] It is desired that one or plural rectifying plates 19, on which a multiplicity of openings are formed so as to partition a flow passage, be provided in the region, in which the filler 16 is filled, in the dissolving tanks 4. The provision of the rectifying plates 19 serves to evenly 25 straighten flows of carbon dioxide and a solvent caused by the filler 16 and an increase in chances, in which the both contact each other, leads to an improvement in dissolution of carbon dioxide in the dissolving tanks 4. Since a retention time in the dissolving tanks 4 and a quantity of dissolved carbon dioxide are substantially in proportion to each other up to the saturated dissolved level, it is desirable to set an apparatus scale so as to accomplish a retention time conformed to a target dissolution quantity under a predetermined operating condition. (0049] Also, in the first component pattern, as shown in Fig. 4, provided in the course of a flow passage extending to the injection well 5 from the dissolving tanks 4 are a separator tank 6 that separates the whole quantity of a carbon dioxide dissolved water as fed into a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state, in which carbon dioxide is dissolved in solubility, and a carbon dioxide pressure feeder 8 that returns the non-dissolved carbon dioxide as separated to an intermediate flow passage between the carbon dioxide compressor 2 and the fine-bubble generating apparatus 7. [0050] The whole quantity of a carbon dioxide dissolved water discharged from the dissolving tanks 4 is accommodated for, 26 and carbon dioxide in a state of being dissolved in a solvent (seawater or water) in level of solubility can be injected under pressure into the underground by separating a non-dissolved carbon dioxide in the separator tank 6 and returning the non-dissolved carbon dioxide to the dissolving tanks 4. Accordingly, the carbon dioxide dissolved water will not contain a non-dissolved carbon dioxide but becomes larger in specific gravity than the peripheral, underground water in an aquifer and is even injected into the aquifer to cause carbon dioxide not to float, thus enabling storing carbon dioxide in the aquifer stably over a long term. [0051] As shown in Fig. 6, the separator tank 6 is provided with an inflow pipe 21, which is provided upright in a closed vessel 20 to have a predetermined height from a lower surface thereof and connected to a flow passage of a carbon dioxide dissolved water passing through the dissolving tanks 4, the carbon dioxide dissolved water is filled substantially in the vessel 20, a non-dissolved carbon dioxide is subjected to gravity separation on an upper side, a non-dissolved carbon dioxide discharge port 22 is formed on an upper part of the vessel 20 to permit the non-dissolved carbon dioxide to be discharged, and a carbon dioxide dissolved water discharge port 23 is formed on a lower part of the vessel 20 to permit a carbon dioxide dissolved water to be discharged after the non-dissolved 27 [0054] In the first component pattern, since a carbon dioxide dissolved water discharged from all the dissolving tanks 4, 4, --- is injected into the separator tank 6 as described above, a non-dissolved carbon dioxide contained in a carbon dioxide dissolved water discharged from the dissolving tanks 4, 4, is completely separated in the separator tank 6 and a carbon dioxide dissolved water in a state, in which carbon dioxide is completely dissolved in the solvent, is injected under pressure into the injection well 5. [0055] [Second component pattern] An underground storage system 1B according to a second component pattern will be described below with reference to Figs. 7 and 8. [0056] As shown in Fig. 7, the underground storage system 1B mainly comprises a carbon dioxide compressor 2 that compresses carbon dioxide to a liquid or supercritical condition, a pressure feeding pump 3 for compression- delivery of a solvent composed of seawater and/or water, a plurality of dissolving tanks 4, 4, --- that allow injection of the compressed carbon dioxide and a solvent thereinto to cause the solvent to dissolve the carbon dioxide thereinto to make a carbon dioxide dissolved water, and an injection well 5 extending from the ground surface 29 carbon dioxide is separated. [0052] Respective flow rates of a solvent and carbon dioxide per one dissolving tank can be found from a weight ratio of carbon dioxide as injected and a solvent (carbon dioxide weight/solvent weight) for a whole flow rate determined by the volume of the dissolving tanks 4 and retention time, during which carbon dioxide and a solvent are retained in the dissolving tanks 4. At this time, the weight ratio of carbon dioxide and a solvent is determined on the basis of a desired dissolution quantity of carbon dioxide. A flow and dissolution test is beforehand made to find the relationship between the weight ratio of carbon dioxide and a solvent and a quantity of dissolved carbon dioxide. [0053] As described in detail in the following embodiments, the concentration of dissolution in the dissolving tanks 4 has influences on the weight ratio of carbon dioxide as injected and a solvent (carbon dioxide weight/solvent weight). Specifically, when the weight ratio as injected increases, the concentration of dissolution in the dissolving tanks 4 tends to increase, so that with a view to promoting dissolution of carbon dioxide, the injected weight ratio of carbon dioxide and a solvent is preferably set to be larger than the target value of concentration of dissolution of carbon dioxide. 28 As shown in Fig. 8, with the dissolving tanks 4, a carbon dioxide injection port 11, into which carbon dioxide fed from the carbon dioxide compressor 2 is injected, and a solvent injection port 12, into which a solvent fed from the solvent pressure feeding pump 3 is injected, are formed on a lower portion of a closed vessel 10, a discharge port 13, through which the carbon dioxide dissolved water is discharged, is formed on an upper portion of the vessel 10, perforated plates 14, 14 are arranged on the upper and lower portions of the vessel 10 to compartment an interior of the vessel 10 vertically, and a granular filler 16 is filled between the perforated plates 14, 14. [0058] In the second component pattern, a branch device 32 may be arranged between the carbon dioxide pressure feeder 8 and the supply pipeline 30 to branch carbon dioxide fed under pressure from the carbon dioxide pressure feeder 8, the branch device 32 may branch that quantity of the carbon dioxide, which can be dissolved in a path extending from the fine-bubble generating apparatus 7 to the aquifer, to feed the same under pressure to the supply pipeline 30, and the remainder of the carbon dioxide may be returned to the dissolving tanks 4. Embodiment 1 [0059] 31 In order to prove a state, in which carbon dioxide was dissolved by the underground storage system 1, a test device shown in Fig. 9 was used to make a dissolution test of carbon dioxide. In addition, the fine-bubble generating apparatus 7 was mounted in the case where a fine-bubble generating apparatus was present in the second embodiment. [0060] With the test device, carbon dioxide in a carbon dioxide cylinder 30 was pressurized by a carbon dioxide compressor 2 to be injected into a dissolving tank 4, salt water in a salt water tank 31 was pressurized by a solvent pressure feeding pump 3 to be injected into the dissolving tank 4, the processing of dissolution of carbon dioxide was performed in the dissolving tank 4, and a carbon dioxide dissolved water was sampled after a non-dissolved carbon dioxide was separated from the carbon dioxide dissolved water in the separator tank. Here, the dissolving tank 4 had a volume of 850 ml and a sand-like material having an average particle size of 0.18 mm (grain 1), 0.63 mm (grain 2), and 1.32 mm (grain 3) was used as a filler 16. In the test, the quantity of carbon dioxide as dissolved was measured for a carbon dioxide dissolved water as sampled when temperature, pressure, flow rate of salt water, grain of the filler 16, and the weight ratio of carbon dioxide and salt water (carbon dioxide weight/salt water weight), respectively, were changed. 32 to the aquifer to allow the resultant carbon dioxide dissolved water to be injected under pressure into the underground aquifer, a separator tank 6 that separates the whole quantity of a carbon dioxide dissolved water as fed into a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state, in which carbon dioxide is dissolved in solubility, and a carbon dioxide pressure feeder 8 that feeds the carbon dioxide as separated in the separator tank 6 are provided in the course of a flow passage extending to the injection well 5 from the dissolving tanks 4, 4, ... , and the fine-bubble generating apparatus 7 is mounted subsequently to the carbon dioxide pressure feeder 8 such that a carbon dioxide supply pipeline 31, to which the carbon dioxide fed under pressure from the carbon dioxide pressure feeder 8 is fed, or a carbon dioxide supply pipeline 31, which is fitted externally onto the main pipeline 30 and to which the carbon dioxide fed under pressure from the carbon dioxide pressure feeder 8 is fed, is arranged in the main pipeline 30, through which the carbon dioxide dissolved water is caused to flow at a predetermined, high flow velocity, small holes are formed on a pipeline wall surface, which partitions the carbon dioxide dissolved water and carbon dioxide, and the carbon dioxide is mixed while being generated fine-bubble by a shearing force of the carbon dioxide dissolved water flowing through the main pipeline 30. [0057] 30 [0061] Figs. 10 and 11, respectively, are graphs showing the relationship between the weight ratio of carbon dioxide injected into the dissolving tank 4 and salt water (carbon dioxide weight/salt water weight), and the quantity of carbon dioxide as dissolved when salt water was changed in flow rate and the filler 16 was changed in grain at respective temperatures. Consequently, there is a tendency that at test temperature being either of 29 *C and 33 *C, the larger the weight ratio of carbon dioxide and salt water and the smaller the filler 16 in grain, the larger the quantity of carbon dioxide as dissolved. [0062] Figs. 12 to 14 are graphs showing the relationship between the weight ratio and the quantity of carbon dioxide as dissolved when salt water was changed in flow rate and pressure was changed at respective temperatures. Consequently, while there is a tendency in the same manner as described above that the larger the weight ratio of carbon dioxide and salt water, the larger the quantity of a carbon dioxide as dissolved, it was confirmed that the quantity of carbon dioxide as dissolved reached a substantially constant, saturated concentration level at a certain weight ratio or more and the underground storage system was effective. [0063] 33 Fig. 15 is a graph showing the relationship between a temperature and the quantity of carbon dioxide as dissolved at respective pressures. Consequently, it was confirmed that the quantity of carbon dioxide as dissolved was not affected much under general temperature conditions in the range of 25 *C to 40 *C. [0064] Fig. 16 is a graph showing the relationship between an average particle size of filler and the quantity of carbon dioxide as dissolved at respective flow rates of salt water. Consequently, in the embodiment, an average particle size of a filler is made at most an average particle size of 1.0 mm to make dissolution of carbon dioxide excellent in efficiency. Embodiment 2 [0065] (Embodiment 2-1) In the Embodiment 2-1, experiments were quantitatively made to examine an effect of dissolution in the fine-bubble generating apparatus 7 of the underground storage system 1 and an effect of dissolution in the dissolving tanks 4. The experiments were made with respect to the case 1: any filler was absent in the dissolving tanks 4 and any fine-bubble generating apparatus 7 was absent, the case 2: any filler was absent in the dissolving tanks 4 and the fine-bubble 34 generating apparatus 7 was present, and the case 3: a filler was present in the dissolving tanks 4 and the fine-bubble generating apparatus 7 was present, and a dissolution test was made for (1) a testing pressure: 15 MPa, a testing temperature: 29 0C, and a (carbon dioxide/salt water) weight ratio: about 8 % and (2) a testing pressure: 15 MPa, a testing temperature: 33 *C, and a (carbon dioxide/salt water) weight ratio: about 8 %. [0066] Fig. 17 shows the results. It could be proved from Fig. 17 that the fine-bubble generating apparatus 7 singly promoted dissolution of carbon dioxide considerably and that a combination of the fine-bubble generating apparatus 7 and the dissolving tanks 4 further promoted dissolution. [0067] (Embodiment 2-2) In the Embodiment 2-2, an experiment was made to verify an effect of promotion of dissolution by the fine-bubble generating apparatus 7. [0068] Generally, it is found that the relationship of the following formula (2) is established between the quantity of carbon dioxide as dissolved and a vessel height Z of a dissolving tank. [Formula 2] 35 Z = (Lm/ Kxa) {lnx* - ln (x* - x)} (2) Here, Z: vessel height (m), Lm: molar flow rate of water section (mol/m 2 s), Kxa: overall volumetric coefficient (mol/m 3 s), x*: saturated dissolved mol fraction, and x: dissolved mol fraction (measurement). [0069] A vessel height Z required for dissolution depended upon an overall volumetric coefficient Kxa, the overall volumetric coefficient Kxa being made an index representative of dissolution efficiency. The experiments in respective cases without any fine-bubble generating apparatus and with a fine-bubble generating apparatus were made for (1) a testing pressure: 15 MPa, a testing temperature: 29 *C, and a weight ratio (carbon dioxide/salt water): about 8 %, (2) a testing pressure: 15 MPa, a testing temperature: 29 *C, and a (carbon dioxide/salt water) weight ratio: about 10 %, and (3) a testing pressure: 15 MPa, a testing temperature: 33 *C, and a (carbon dioxide/salt water) weight ratio: about 8 %, and as shown in Figs. 13 to 15, graphs were obtained, in which an axis of ordinate indicates overall volumetric coefficients Kxa (mol/m3S) and an axis of abscissa indicates molar flow velocity of water section (mol/(m 2 s)). In the graphs of Figs. 13 to 15, in a region, in which the molar flow velocity of water section (mol/ (m2- s) ) was high, an overall volumetric coefficient Kxa in the case with a fine-bubble generating 36 apparatus was at least 1.5 times that in the case without any fine-bubble generating apparatus. (0070] (Embodiment 2-3) The test result in the Embodiment 2-2 was rearranged with the use of Weber number We shown in formula (1) to present a graph as shown in Fig. 21, in which an axis of ordinate indicates overall volumetric coefficient ratios Kxa (B) / Kxa (NB) [here, Kaa (B) : overall volumetric coefficient with a fine-bubble generating apparatus, Kxa (NB) : overall volumetric coefficient without any fine-bubble generating apparatus], and an axis of abscissa indicates Weber number We. [0071] It was found from the figure that fine-bubble generation had a high dissolution efficiency in a region, in which the Weber number we was at least 10. Accordingly, it is desired in the fine-bubble generating apparatus 7 to set a flow velocity of a solvent and a diameter of small holes 30a(31a) so that the Weber number we is made at least 10. However, this was on condition that the flow velocity of carbon dioxide from the small holes is at least 8x10- 2 m/s according to the test. Brief Description of the Drawings [0072] [Fig. 1] Fig. 1 is a longitudinal, cross sectional view 37 showing a fine-bubble generating apparatus 7A according to a first embodiment. [Fig. 2] Fig. 2 is a longitudinal, cross sectional view showing a fine-bubble generating apparatus 7B according to a second embodiment (1). [Fig. 3] Fig. 3 is a longitudinal, cross sectional view showing a fine-bubble generating apparatus 7C according to the second embodiment (2). [Fig. 4] Fig. 4 is a conceptual view showing a carbon dioxide underground storage system 1A (first component pattern) according to the invention. [Fig. 5] Fig. 5 is a longitudinal, cross sectional view showing a dissolving tank 4. [Fig. 6] Fig. 6 is a longitudinal, cross sectional view showing a separator tank 6. [Fig. 7] Fig. 7 is a conceptual view showing a carbon dioxide underground storage system 1B (second component pattern) according to the invention. [Fig. 8] Fig. 8 is a longitudinal, cross sectional view showing a dissolving tank 4. [Fig. 9] Fig. 9 is a conceptual view showing a test device. [Fig. 10] Fig. 10 is a graph showing the relationship between a carbon dioxide/salt water weight ratio and the quantity of carbon dioxide as dissolved at temperature 29 0C 38 in the first embodiment when conditions of grain and a flow rate of salt water are changed. [Fig. 11] Fig. 11 is a graph showing the relationship between a carbon dioxide/salt water weight ratio and the quantity of carbon dioxide as dissolved at temperature 33 0C in the first embodiment when conditions of grain and a flow rate of salt water are changed. [Fig. 12] Fig. 12 is a graph showing the relationship between a carbon dioxide/salt water weight ratio and the quantity of carbon dioxide as dissolved at temperature 25 OC in the first embodiment when conditions of pressure and a flow rate of salt water are changed. [Fig. 133 Fig. 13 is a graph showing the relationship between a carbon dioxide/salt water weight ratio and the quantity of carbon dioxide as dissolved at temperature 29 0C in the first embodiment when conditions of pressure and a flow rate of salt water are changed. [Fig. 14] Fig. 14 is a graph showing the relationship between a carbon dioxide/salt water weight ratio and the quantity of carbon dioxide as dissolved at temperature 33 *C in the first embodiment when conditions of pressure and a flow rate of salt water are changed. [Fig. 15] Fig. 15 is a graph showing the relationship between temperature and the quantity of carbon dioxide as dissolved in the first embodiment. 39 [Fig. 161 Fig. 16 is a graph showing the relationship between an average particle size of filler and the quantity of carbon dioxide as dissolved in the first embodiment. [Fig. 17] Fig. 17 is a graph quantitatively showing results of a verification experiment for an effect of dissolution in a fine-bubble generating apparatus 7 and an effect of dissolution in a dissolving tank 4 in an Embodiment 2-1. [Fig. 18] Fig. 18 is a graph (1) representative of the relationship between an overall volumetric coefficient Kxa and a molar flow velocity of water section in an Embodiment 2-2. [Fig. 19] Fig. 19 is a graph (2) representative of the relationship between an overall volumetric coefficient Kxa and a molar flow velocity of water section in the Embodiment 2-2. [Fig. 20] Fig. 20 is a graph (3) representative of the relationship between an overall volumetric coefficient Kxa and a molar flow velocity of water section in an Embodiment 2-2. [Fig. 21] Fig. 21 is a graph representative of the relationship between an overall volumetric coefficient ratio Kxa(B)/ Kxa(NB) and Weber number We in an Embodiment 2-3. Description of Reference Numerals and Signs [0073] 1A-1B: underground storage system, 2: carbon dioxide compressor, 3: solvent pressure feeding pump, 4: dissolving 40 tank, 5: injection well, 6: separator tank, 7: fine-bubble generating apparatus, 8: carbon dioxide pressure feeder, 10: vessel, 11: carbon dioxide injection port, 12: solvent injection port, 13: discharge port, 14: perforated plate, 15: mesh plate, 16: filler, 19: rectifying plate, 20: vessel, 21: inflow pipe, 22: non-dissolved carbon dioxide discharge port, 23: carbon dioxide discharge port, 30: main pipeline, 31: carbon dioxide supply pipeline, 30a-31a: small hole, 32: branch device 41