AU2008236123B2

AU2008236123B2 - Carbon dioxide underground reserving system

Info

Publication number: AU2008236123B2
Application number: AU2008236123A
Authority: AU
Inventors: Hirokazu Kishi; Masayuki Masuda; Yuji Sekine
Original assignee: Tokyo Electric Power Co Inc
Current assignee: Tokyo Electric Power Co Holdings Inc
Priority date: 2007-03-27
Filing date: 2008-03-25
Publication date: 2012-08-02
Anticipated expiration: 2028-03-25
Also published as: JP2008238054A; JP4924140B2; AU2008236123A1; WO2008123222A1

Abstract

[PROBLEMS] To effect long-term stable reservation/isolation of carbon dioxide in an aquifer by pressure feeding into the aquifer the carbon dioxide in the state of being dissolved in a solvent (seawater or water) at high concentration close to the level of saturation concentration. [MEANS FOR SOLVING PROBLEMS] The system comprises a carbon dioxide compressor (2) for compressing carbon dioxide to a liquid or supercritical condition; a pressure feeding pump (3) for effecting compression/delivery of a solvent consisting of seawater and/or water; one or more dissolving tanks (4) for allowing injection of compressed carbon dioxide and solvent therein to thereby cause the solvent to dissolve the carbon dioxide into a carbon dioxide dissolution water; and an injection well (5) extending from the ground surface to the aquifer, used to press fit the resultant carbon dioxide dissolution water into the underground aquifer. Each of the dissolving tanks (4) has a hermetically sealed container (10) provided at its inferior portion with a carbon dioxide fill port (11) for injection of carbon dioxide fed from the carbon dioxide compressor (2) and with a solvent fill port (12) for injection of the solvent fed from the solvent pressure feeding pump (3). The container (10) is filled with a granular filler (16).

Description

Description CARBON DIOXIDE UNDERGROUND STORAGE SYSTEM Technical Field (0001] The present invention relates to a carbon dioxide underground storage system that injects carbon dioxide, which is captured from a large scale discharge source of carbon dioxide, or the like, under pressure into a ground to store the same stably over a long term in order to contribute to reduction of carbon dioxide, which is one of greenhouse effect gases responsible for global warming. 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 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. 1 [0003] 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, there arises a problem 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 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 CO 2 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 2 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. 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 [0005] With the methods described in the Patent Documents 1 to 3, however, carbon dioxide is dissolved at a high concentration 3 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 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". Also, there is a fear that it is not possible to confirm the quantity of carbon dioxide as dissolved according to a location of dissolution. [0006] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. [0006A] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be 4 understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Disclosure of the Invention [0007] According to the invention, there is provided 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, a pressure feeding pump that performs compression and 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-water solution, and an injection well extending from the ground surface to the aquifer to have the resultant carbon dioxide-water solution 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 5 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 the carbon dioxide-water solution is discharged, and filled with a granular filler. [0008] According to an embodiment of the invention, 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 the carbon dioxide-water solution is discharged, and filled with a granular filler, whereby carbon dioxide (a liquid or supercritical condition) can be dissolved at a high concentration around a saturated concentration level into a solvent (seawater or water) in the dissolving tanks, so that the carbon dioxide-water solution is made larger in specific gravity than a peripheral underground water, thus enabling storing carbon dioxide in an aquifer stably over a long term. [0009] The granular filler may be composed of any one of, or a 6 combination of sand, crushed stone, Raschig ring, and saddle. [0010] According to an embodiment of the invention, 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. [0011] The granular filler may have an optimum, average particle size, which is determined for each kind of filler 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. [0012] According to an embodiment of the invention, 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 dissolving tanks, for each kind of a filler, so that an average particle size amounting to the optimum, average particle size is excellent in efficiency of dissolution. [0013] One or plural rectifying plates, on which a multiplicity of openings are formed so as to partition a flow passage, may 7 be provided in the filled region of the filler. According to an embodiment of the invention, the rectifying plates are provided to thereby promote dissolution of carbon dioxide in the dissolving tanks. [00141 A separator tank that separates a non-dissolved carbon dioxide and a carbon dioxide- water solution in a state where carbon dioxide is dissolved in saturated concentration in the whole quantity of a carbon dioxide- water solution, 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 may be provided in the course of a flow passage extending to the injection well from the dissolving tank. [0015) According to an embodiment of the invention, a non-dissolved carbon dioxide is separated in the separator tank from the whole quantity of a carbon dioxide- water solution created in the dissolving tanks and the non-dissolved carbon dioxide is returned to the dissolving tanks whereby injection under pressure into the ground is made possible in a state, in which carbon dioxide is dissolved at a saturated concentration level into a solvent (seawater or water) . The carbon dioxide-water solution is made larger in specific gravity than 8 a peripheral underground water in the aquifer, so that even when injected into an aquifer, carbon dioxide will not float but can be stored in an aquifer stably over a long term. [0016] A plurality of the dissolving tanks may be arranged, wherein, for a part of the dissolving tanks, a separator tank, by which a carbon dioxide-water solution as fed is separated into a non-dissolved carbon dioxide and a carbon dioxide-water solution in a state in which carbon dioxide is dissolved in saturated concentration, is arranged midway a flow passage extending to an injection well from a dissolving tank, 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 is arranged, and wherein, for the remainder of the dissolving tanks, a flow passage is connected to a downstream side of the separator tank. [0017] According to an embodiment of the invention, control is exercised in expectation of dissolution of carbon dioxide into the underground water to inject carbon dioxide under pressure into the underground aquifer in a state, in which a non-dissolved carbon dioxide is contained (5 % of solvent weight at maximum), to dissolve the non-dissolved carbon dioxide into 9 the underground water. In addition, only a period of time, during which carbon dioxide is injected under pressure and the carbon dioxide flows in the aquifer, is taken into consideration as a period of time, during which carbon dioxide is dissolved into the underground water. Comparing the invention according to this embodiment with the invention according to embodiment discussed above it, it is possible to decrease a quantity of seawater or water as used and energy required for the processing per unit weight of carbon dioxide. [0018] A carbon dioxide-water solution discharged from the dissolving tanks may be injected under pressure into the underground aquifer while being put in a state of containing a non-dissolved carbon dioxide. [0019] According to an embodiment of the invention, it is possible to promote a reduction of a quantity of seawater or water as used and energy required for the processing per unit weight of carbon dioxide. Any separator is dispensed with by adjusting the quantity of carbon dioxide introduced into the dissolving tanks so as to make a non-dissolved carbon dioxide non-existent in the aquifer after the lapse of a period of time, during which carbon dioxide is injected into the aquifer, and it becomes possible to reduce the quantity of seawater or water 10 as used and energy as used. [0020] As described above in detail, it is possible according to embodiments of the invention to store carbon dioxide in an aquifer stably over a long term in a state, in which carbon dioxide is dissolved at a high concentration around a saturated concentration level into a solvent. Best Mode for Carrying Out the Invention [0021] Embodiments of the invention will be described below with reference to the drawings. [0022] A carbon dioxide underground storage system 1 according to the an embodiment of the invention traps carbon dioxide, which is captured from a large scale exhaust 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. [0023] In this manner, since 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 and carbon dioxide 11 is stored into an aquifer stably over a long term, a target quantity of dissolution of carbon dioxide in embodiments of the invention is 40 to 50 kg, preferably 45 to 50 kg per 1 m3 of a solvent. [0024] 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 under pressure into the underground aquifer, and a pressure loss in a piping system. [0025] [First component pattern] Fig. 1 is a conceptual view showing a first component pattern of a carbon dioxide underground storage system 1 according to an embodiment of the invention. As shown in Fig. 1, the carbon dioxide underground storage system 1 comprises a carbon dioxide compressor 2 that compresses carbon dioxide to a liquid or supercritical condition, a pressure feeding pump 3 for compression and 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 therein to cause the solvent to dissolve the carbon dioxide to make a carbon dioxide dissolved water, and an injection well 5 extending from 12 the ground surface to an aquifer to allow the carbon dioxide dissolved water as created to be injected under pressure into the underground aquifer. [0026] In addition, according to the embodiment, the dissolving tanks 4 are mounted in plural to promote dissolution of carbon dioxide but one tank will do at need. [0027] As shown in Fig. 2, with the dissolving tanks 4, a carbon dioxide injection port 11, through which carbon dioxide fed from the carbon dioxide compressor 2 is injected, and a solvent injection port 12, through 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, 15 are arranged on upper and lower portions in the vessel 10 to compartment an interior of the vessel 10 vertically, and a granular filler 16 is filled between the perforated plates 14, 15. [0028] 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 13 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 a 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. [0029] Also, the filler 16 has preferably 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 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 an optimum, average particle size every kind of a filler. (1) The relationship between an average particle size of a 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 a filler and a pressure loss of a dissolving tank 14 [0030] 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 dissolution quantity of 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. In addition, in the case where a predetermined quantity of dissolved carbon dioxide cannot be determined, it is taken into consideration to adopt measures for making a dissolving tank large in size. [0031] A filler 16 having the optimum, average particle size is used to lead to an excellent dissolution efficiency of carbon dioxide. [0032] As shown in Fig. 2, 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, 15 it is possible to form a construction having 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. [0033] Here, in explaining flow in the dissolving tanks 4 with reference to Fig. 2, carbon dioxide and a solvent, which are fed under pressure into the vessel 10 from the carbon dioxide injection port 11 and the solvent injection port 12, are mixed together in a lower hopper portion 17 and enter a region, in which the filler 16 is filled, evenly from the lower, perforated plate 14. 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 an upper, perforated plate 15, 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 15 is discharged from the discharge port 13. [0034] It is desired that one or plural rectifying plates 19, on which a multiplicity of openings are formed so as to 16 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 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. [0035] Also, in the first component pattern, 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 a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state where carbon dioxide is dissolved in saturated concentration in the whole quantity of a carbon dioxide dissolved water, and a carbon dioxide pressure feeder 7 that returns the non-dissolved carbon dioxide as separated to an intermediate flow passage between the carbon dioxide compressor 2 and the dissolving tanks 4. [0036] In the first component pattern, the whole quantity of 17 a carbon dioxide dissolved water created in the dissolving tanks 4 is accommodated for, and carbon dioxide in a state of being dissolved in a solvent (seawater or water) in level of solubility can be fed 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. The carbon dioxide dissolved water will become larger in specific gravity than the peripheral, underground water around 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. [0037] As shown in Fig. 3, 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 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 18 carbon dioxide is separated. [0038] Respective flow rates of a solvent and carbon dioxide per one dissolving tank 1 can be found from a whole flow rate determined by 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 by 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 dissolution quantity of carbon dioxide. [0039] 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 a target value of concentration of dissolution of carbon dioxide. 19 [0040] 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, 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. [0041] [Second component pattern] A second component pattern is the same in main components of a carbon dioxide underground storage system 1 as the first component pattern but different in the following points therefrom. That is, as shown in Fig. 4, a plurality of dissolving tanks 4 are arranged, for a part of the dissolving tanks 4, a separator tank 6, by which a carbon dioxide dissolved water as fed is separated into a non-dissolved carbon dioxide and a carbon dioxide dissolved water in a state, in which carbon dioxide is dissolved in saturated concentration, is arranged midway a flow passage extending to an injection well 5 from a dissolving tank 4 and a carbon dioxide pressure feeder 7 that returns the non-dissolved carbon dioxide as separated to an intermediate flow passage between the carbon dioxide compressor 2 and the dissolving tank 4, is arranged, while for 20 the remainder of the dissolving tanks, a flow passage is connected to a downstream side of the separator tank 6. [0042] In the second component pattern, control is exercised in expectation of dissolution of carbon dioxide into the underground water to inject carbon dioxide under pressure into the underground aquifer in a state, in which a non-dissolved carbon dioxide is contained (5 % of solvent weight at maximum), to dissolve the non-dissolved carbon dioxide into the underground water. In addition, only a period of time, during which carbon dioxide is injected under pressure and the carbon dioxide flows in the aquifer, is taken into consideration as a period of time, during which carbon dioxide is dissolved into the underground water. [0043] As compared with the first component pattern, the second component pattern enables reducing a quantity of seawater or water as used and energy required for the processing of carbon dioxide per unit weight of carbon dioxide. [0044) [Third component pattern] As shown in Fig. 5, a third component pattern is different from the first component pattern in that a carbon dioxide dissolved water discharged from dissolving tanks 4 is injected under pressure into the underground aquifer while being put in a state of containing a non-dissolved carbon dioxide. 21 [0045] The third component pattern promotes reduction of a quantity of seawater or water as used and energy required for the processing per unit weight of carbon dioxide. In the third component pattern, a non-dissolved carbon dioxide (5 % of solvent weight at maximum) is controlled in expectation of dissolution of carbon dioxide into the underground water so as to accomplish dissolution of carbon dioxide into the underground water in the underground aquifer. Only a period of time, during which a non-dissolved carbon dioxide is injected and the carbon dioxide flows in the aquifer, is taken into consideration as a period of time, during which carbon dioxide is dissolved into the underground water. In the dissolving tanks 4, any separator is dispensed with by adjusting the quantity of carbon dioxide introduced into the dissolving tanks so as to make a non-dissolved carbon dioxide non-existent in the aquifer after the lapse of the period of time, and it becomes possible to reduce the quantity of seawater or water as used and energy as used. Embodiment [0046] In order to prove a state, in which carbon dioxide is dissolved by the carbon dioxide underground storage system 1, a test device shown in Fig. 6 was used to make a dissolution test of carbon dioxide. 22 [0047] As shown in Fig. 6, 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 dissolving 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. [0048] Figs. 7 and 8, 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 23 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. [0049] Figs. 9 to 11 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, in the same manner as described above, while there is a tendency 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 carbon dioxide underground storage system was effective. [0050] Fig. 12 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. 24 [0051] Fig. 13 is a graph showing the relationship between an average particle size of a 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. Brief Description of the Drawings [0052] [Fig. 1] Fig. 1 is a conceptual view showing a carbon dioxide underground storage system 1 (first component pattern) according to an embodiment of the invention. [Fig. 2] Fig. 2 is a longitudinal, cross sectional view showing a dissolving tank 4. [Fig. 3) Fig. 3 is a longitudinal, cross sectional view showing a separator tank 6. [Fig. 4] Fig. 4 is a conceptual view showing a carbon dioxide underground storage system 1 (second component pattern) according to an embodiment of the invention. [Fig. 5] Fig. 5 is a conceptual view showing a carbon dioxide underground storage system 1 (third component pattern) according to an embodiment of the invention. [Fig. 6] Fig. 1 is a conceptual view showing a test device. [Fig. 7] Fig. 7 is a graph showing the relationship 25 between the weight ratio for a flow rate of salt water and grain, and the quantity of carbon dioxide as dissolved at temperature 29 *C. [Fig. 8] Fig. 8 is a graph showing the relationship between the weight ratio for a flow rate of salt water and grain, and the quantity of carbon dioxide as dissolved at temperature 33 *C. [Fig. 9] Fig. 9 is a graph showing the relationship between the weight ratio for a flow rate of salt water and pressure, and the quantity of carbon dioxide as dissolved at temperature 25 0 C. [Fig. 10] Fig. 10 is a graph showing the relationship between the weight ratio for a flow rate of salt water and pressure, and the quantity of carbon dioxide as dissolved at temperature 29 0 C. [Fig. 11] Fig. 11 is a graph showing the relationship between the weight ratio for a flow rate of salt water and pressure, and the quantity of carbon dioxide as dissolved at temperature 33 *C. [Fig. 12] Fig. 12 is a graph showing the relationship between temperature and the quantity of carbon dioxide as dissolved. [Fig. 13] Fig. 13 is a graph showing the relationship between an average particle size of filler and the quantity of carbon dioxide as dissolved. 26 Description of Reference Numerals and Signs (0053] 1: underground storage system, 2: carbon dioxide compressor, 3: solvent pressure feeding pump, 4: dissolving tank, 5: injection well, 6: separator tank, 7: carbon dioxide pressure feeder, 10: vessel, 11: carbon dioxide injection port, 12: solvent injection port, 13: discharge port, 14, 15: perforated plate, 16: filler, 19: rectifying plate, 20: vessel, 21: inflow pipe, 22: non-dissolved carbon dioxide discharge port, 23: carbon dioxide discharge port 27 Fig. 1 2: CARBON DIOXIDE COMPRESSOR 3: SOLVENT PRESSURE FEEDING PUMP 4: DISSOLVING TANK 5: INJECTION WELL 6: SEPARATOR TANK 7: CARBON DIOXIDE PRESSURE FEEDER a: NON-DISSOLVED CARBON DIOXIDE b: GROUND LAYER c: AQUIFER (STORAGE LAYER) Fig. 2 a: CARBON DIOXIDE DISSOLVED WATER b: CARBON DIOXIDE c: SOLVENT Fig. 3 a: NON-DISSOLVED CARBON DIOXIDE b: INTERFACE c: CARBON DIOXIDE DISSOLVED WATER d: NON-DISSOLVED CARBON DIOXIDE BUBBLE Fig. 4 a: NON-DISSOLVED CARBON DIOXIDE b: CARBON DIOXIDE DISSOLVED WATER 28 c: CARBON DIOXIDE d: SOLVENT Fig. 6 a: PRESSURE HOLDING VALVE b: SALT WATER Fig. 7 a: TEMPERATURE b: QUANTITY OF CARBON DIOXIDE AS DISSOLVED c: WEIGHT RATIO % (CARBON DIOXIDE/SALT WATER) d: FLOW RATE OF SALT WATER e: GRAIN Fig. 9 f: PRESSURE 29

Claims

1. 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, a pressure feeding pump that performs compression and 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 a carbon dioxide water solution, and an injection well extending from the ground surface to the aquifer to have the resultant carbon dioxide-water solution 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 the carbon dioxide-water solution is discharged, and filled with a granular filler.

2. The carbon dioxide underground storage system according to claim 1, wherein the granular filler is composed of any one 30 of, or a combination of sand, crushed stone, Raschig ring, and saddle.

3. The carbon dioxide underground storage system according to claim 1 or 2, wherein the granular filler has an optimum, average particle size, which is determined for each kind of filler 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.

4. The carbon dioxide underground storage system according to any one of claims 1 to 3, 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.

5. The carbon dioxide underground storage system according to any one of claims 1 to 4, wherein a separator tank that separates a non-dissolved carbon dioxide and a carbon dioxide-water solution in a state where carbon dioxide is dissolved in saturated concentration in the whole quantity of a carbon dioxide-water solution, 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.

6. The carbon dioxide underground storage system according to any one of claims 1 to 4, 31 wherein a plurality of the dissolving tanks are arranged, wherein, for a part of the dissolving tanks, a separator tank, by which a carbon dioxide- water solution as fed is separated into a non-dissolved carbon dioxide and a carbon dioxide-water solution in a state in which carbon dioxide is dissolved in saturated concentration, is arranged midway in a flow passage extending to an injection well from a dissolving tank, 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 is arranged, and wherein, for the remainder of the dissolving tanks, a flow passage is connected to a downstream side of the separator tank.

7. The carbon dioxide underground storage system according to any one of claims 1 to 4, wherein a carbon dioxide-water solution discharged from the dissolving tanks is injected under pressure into the underground aquifer while being put in a state of containing a non-dissolved carbon dioxide.

8. A carbon dioxide underground storage system substantially as hereinbefore described with reference to the accompanying drawings. 32