ARTIFICIAL GROUND FREEZING METHOD AND ARTIFICIAL GROUND FREEZING SYSTEM

Abstract

The purpose of the present invention is to provide an artificial ground freezing method having good coolant thermal efficiency without a gas-phase coolant being released into the ground or into the air. For that purpose, the present invention has: a freeze pipe (1: casing) for freezing the ground buried in the ground and a coolant circulation pipe (2) provided on the inside of the freeze pipe (1), wherein the coolant flowing inside the coolant circulation pipe (2) is carbon dioxide; and a coolant apparatus (10) that cools and supplies the carbon dioxide to the coolant circulation pipe (2), the coolant circulation pipe (2) comprising a first coolant circulation pipe (2A) on which a plurality of micro-coolant passages (2A delta) is formed, wherein the tip portion (tip portion in the ground) of the first coolant circulation pipe (2A) is connected to a plugging member (3: bottom socket) that connects the plurality of micro-coolant passages (2A delta) of the first coolant circulation pipe (2A) to a coolant supply side and coolant return side.

Claims

1: An artificial ground freezing system characterized in that: the system comprises a coolant apparatus which cools and supplies the coolant to a coolant circulation pipe, and a coolant circulating in the coolant circulation pipe is carbon dioxide; the coolant circulation pipe comprises a first coolant circulation pipe having a plurality of micro-coolant passages formed inside thereof; and that a tip portion of the first coolant circulation pipe is connected with a plugging member which communicates a coolant supply side of the plurality of micro-coolant passages of the first coolant circulation pipe with a coolant return side thereof.

2: The artificial ground freezing system according to claim 1, wherein said system comprises: a freeze pipe being buried in order to freeze a ground; and a coolant circulation pipe being provided inside of the freeze pipe.

3: The artificial ground freezing system according to claim 1, wherein an end on the coolant supply side of the first coolant circulation pipe is connected with a connecting member which divides the plurality of micro-coolant passages of the first coolant circulation pipe into the coolant supply side and the coolant return side, and wherein the coolant supply side and the coolant return side of the plurality of micro-coolant passages of the first coolant circulation pipe are connected with second coolant circulation pipes through the connecting member.

4: The artificial ground freezing system according to claim 3, wherein the connecting member is provided in the ground.

5: The artificial ground freezing system according to claim 3, wherein the connecting member is provided at a region being closer to the coolant supply side than the ground.

6: The artificial ground freezing system according to claim 1, wherein a heat transfer fluid is filled in a region corresponding to the ground to be frozen, and an insulator is provided in a region corresponding to the ground not to be frozen.

7: An artificial ground freezing method characterized in that an artificial ground freezing system is used in the method, said system comprises a coolant apparatus for cooling and supplying the coolant to the coolant circulation pipe, and a coolant circulating in the coolant circulation pipe is carbon dioxide; liquid-phase carbon dioxide circulates in the coolant circulation pipe comprises a first coolant circulation pipe having a plurality of micro-coolant passages formed therein carbon dioxide supplied from the coolant apparatus on a coolant supply side flows in some portions of the plurality of micro-coolant passages of the first coolant circulation pipe having the tip portion to which a plugging member is connected, and carbon dioxide flows toward the coolant supply side in the other portions of the plurality of micro-coolant passages on a coolant return side.

8: The artificial ground freezing method according to claim 7, wherein said artificial ground freezing system comprises a freeze pipe being buried in order to freeze a ground and a coolant circulation pipe being provided inside of the freeze pipe.

9: The artificial ground freezing method according to claim 7, wherein an end on the coolant supply side of the first coolant circulation pipe is connected with a connecting member, and carbon dioxide flowing on the coolant supply side of the plurality of micro-coolant passages of the first coolant circulation pipe and carbon dioxide flowing on the coolant return side flow on a coolant supply side and a coolant return side of second coolant circulation pipes, respectively, through the connecting member.

10: The artificial ground freezing method according to claim 9, wherein the connecting member is provided in the ground.

11: The artificial ground freezing method according to claim 9, wherein the connecting member is provided in a region being closer to the coolant supply side than the ground.

12: The artificial ground freezing method according to claim 7, comprising: a step for filling a heat transfer fluid in a region corresponding to the ground to be frozen; and a step for providing an insulator in a region of the ground not to be frozen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0063] FIG. 1 is a block diagram showing an abstract of an artificial ground freezing method according to one of the embodiments of the present invention;

[0064] FIG. 2 is a perspective cross-sectional view showing a partially the coolant circulation pipe according to one of the embodiments of the present invention;

[0065] FIG. 3 is an explanatory drawing showing coolant circulation pipes, a plugging member and a connecting member according to the first embodiment of the present invention;

[0066] FIG. 4 is a perspective view showing constructions of the freeze pipe according to the first embodiment;

[0067] FIG. 5 is a front cross-sectional view of the freeze pipe shown in FIG. 4;

[0068] FIG. 6 is a front cross-sectional view showing a freeze pipe according to the second embodiment of the present invention;

[0069] FIG. 7 is an explanatory drawing showing an end of the coolant circulation pipe according to the second embodiment;

[0070] FIG. 8 is a perspective view showing a situation that the coolant circulation pipe is inserted into the freeze pipe according to the second embodiment;

[0071] FIG. 9 is a plan view showing a spacer according to the second embodiment which spacer is used in a case that a plurality of the coolant circulation pipes are inserted into the freeze pipe;

[0072] FIG. 10 is a cross-sectional view showing a situation that a plurality of coolant circulation pipes are inserted into the freeze pipe according to an alternative example of the first embodiment and the second embodiment;

[0073] FIG. 11 is a perspective view showing a coolant circulation pipe according to a third embodiment of the present invention;

[0074] FIG. 12 is a front cross-sectional view showing the coolant circulation pipe, a plugging member and a connecting member according to the third embodiment;

[0075] FIG. 13 is a fragmentary cross-sectional view showing one example of constructions of a joint member of the coolant circulation pipe;

[0076] FIG. 14 is a perspective view showing constructions of another joint member of the coolant circulation pipes according to the third embodiment not shown in FIG. 12;

[0077] FIG. 15 is an explanatory drawing showing an alternative example of the first embodiment;

[0078] FIG. 16 is an explanatory drawing showing a brine heat exchange cycle;

[0079] FIG. 17 is an explanatory drawing showing an another example of the plugging member according to the first embodiment;

[0080] FIG. 18 is an explanatory drawing showing a further alternative example of the plugging member according to the first embodiment;

[0081] FIG. 19 is an explanatory drawing showing an alternative example of the connecting member according to the first embodiment;

[0082] FIG. 20 is an explanatory drawing showing a further alternative example of the connecting member according to the first embodiment; and

[0083] FIG. 21 is an explanatory drawing showing a more one example of the connecting member according to the first embodiment not shown in FIGS. 19 and 20.

DESCRIPTION OF EMBODIMENTS

[0084] Embodiments of the present invention will be described with reference to the accompanying drawings.

[0085] FIG. 1 shows an outline of a heat exchange cycle according to the first embodiment and the second embodiment shown in the drawings.

[0086] In FIG. 1, a plurality of freeze pipes 1 (casing) for freezing a ground G are buried in the ground (2 pipes in FIG. 1), and the freeze pipes 1 (casing) are provided with coolant circulation pipes 2 in parallel. A secondary coolant which circulates in the coolant circulation pipes 2 is carbon dioxide (CO.sub.2), said liquid-phase carbon dioxide being supplied from a part above the ground performs heat exchange with the ground G, and said liquid-phase carbon dioxide freezes the ground G by sensible heat or latent heat of vaporization thereof.

[0087] The artificial ground freezing system shown in FIG. 1 includes a coolant apparatus 10 and a coolant circulation pump 11, said coolant apparatus 10 cools the liquid-phase carbon dioxide and supplies it to the freeze pipe 1. The coolant apparatus 10 includes a liquefier 10A (carbon dioxide liquefier), a condenser 10B, and a cooling tower 10C.

[0088] In the liquefier 10A, carbon dioxide, which has been subjected heat exchange with the ground G while circulating in the coolant circulation pipes 2, is subjected to heat exchange with a primary coolant, and a phase thereof is changed into low-temperature liquid-phase carbon dioxide, and the low-temperature liquid-phase carbon dioxide is supplied to the coolant circulation pipes 2 again in order to circulate therein.

[0089] The primary coolant circulating in the coolant apparatus 10 is, for example, a coolant R404a etc., the carbon dioxide as a secondary coolant is evaporated and vaporized by heat supplied from the ground G, and is cooled and condensed by heat exchange with water in the condenser 10B. The water warmed in the condenser 10B by heat of vaporization of the primary coolant (e.g., coolant R404a) is cooled by the cooling tower 10C.

[0090] In FIG. 1, coolant circulation pipes 2 are inserted into two freeze pipes 1 in parallel, but an arrangement of the coolant circulation pipes is not specifically restricted in this construction (it is possible to position the coolant circulation pipes in a serial arrangement). In a case that liquid-phase carbon dioxide as a coolant (secondary coolant) can keep cold energy enough to freeze the soil around the pipes, the coolant circulation pipes 2 may be inserted into a plurality of freeze pipes 1 in serial arrangement.

[0091] A freeze pipe may be a casing adopted from for drilling equipment, for instance, in a condition buried in the ground, and protect a collapse of a borehole wall. It is possible to provide the coolant circulation pipes 2 in a borehole (not shown) being provided into the ground, without using of freeze pipes 1.

[0092] In the artificial ground freezing method shown in FIG. 1, liquid-phase carbon dioxide is applied or used as a secondary coolant, the liquid-phase carbon dioxide being supplied from an apparatus (not shown) on the ground cools the ground G or absorbs latent heat of vaporization from the ground G, and then freezes the ground. Accordingly, this method is better in thermal efficiency than a prior art method in which sensible heat of a (brine) coolant is applied.

[0093] Herein, the artificial ground freezing system shown in FIG. 1, liquid-phase carbon dioxide circulates in a closed system. In this system, it is not necessary to release coolant gas into the ground, and also, it is not necessary to release coolant gas into the atmosphere. Accordingly, since the artificial ground freezing method shown in FIG. 1 can reduce liquefied gas consumption quantity, the method shown in FIG. 1 is more effective in an economical aspect than a prior art method in which liquefied gas is used as a coolant. Additionally, in the artificial ground freezing method shown in FIG. 1, since coolant gas is not released at a construction site, oxygen concentration is not reduced and it is prevented that construction worker should be worked in an environment in which oxygen concentration is reduced and becomes an oxygen-deficient environment.

[0094] In addition, since the coefficient of viscosity of liquid-phase carbon dioxide is extremely small which is approximate 1/90 times the coefficient of viscosity of brine, it is possible to reduce cross-section of the second coolant circulation pipes and to increase the flow rate of the second coolant circulating in the second coolant circulation pipe.

[0095] Additionally, in a case that liquid-phase carbon dioxide circulates as a secondary coolant, there is a case that the liquid-phase carbon dioxide is vaporized while passing through the ground, and then, in this case, a mixture of a liquid-phase coolant and a gas-phase coolant flow in the coolant circulation pipes and the viscosity thereof is reduced further.

[0096] Accordingly, the artificial ground freezing system shown in FIG. 1 can reduce the diameter of a freeze pipe and employ a longer freeze pipe. Consequently, the artificial ground freezing system shown in FIG. 1 can reduce the capacity of the coolant circulation pump 11 to reduce machine rental costs and pump driving energy.

[0097] Then, in the system shown in FIG. 1, since the cross-section area of the coolant circulation pipes 2 for flowing liquid-phase carbon dioxide can be reduced, the flat member shown in FIG. 2 (having a micro-coolant passage 2Aδ) can be used as the coolant circulation pipe 2A (first coolant circulation pipe: e.g., aluminum).

[0098] In FIG. 2, a first coolant circulation pipe 2A being entirely made of a flat member includes a micro channel structure having a plurality of micro-coolant passages 2Aδ (10 micro-coolant passages in the embodiment shown) a cross-section of each of which is quadrangle (rectangle). The first coolant circulation pipe 2A is made of e.g., aluminum and excellent in thermal characteristics typical of a micro channel structure.

[0099] In FIG. 2, a cross-section of the micro-coolant passage 2Aδ is rectangle in order to increase a contact area between the inner peripheral surface of the micro-coolant passage 2Aδ and a coolant (for example, contact area between an aluminum micro-coolant passage 2Aδ and a coolant), and then, to improve an effect of freezing of a coolant. However, it is possible to make the cross-section of the micro-coolant passage 2Aδ non-rectangle (e.g., circle).

[0100] Additionally, in this specification, the coolant circulation pipe 2A (first coolant circulation pipe) being in the form of flat member shown in FIG. 2, can be referred to as “micro channel.” Also, in this specification, a coolant circulation pipe 3C, in the form of hollow cylinder (pipe) shown in FIGS. 11 to 14, can be referred to as “micro channel.”

[0101] According to the first embodiment of the present invention, when a first coolant circulation pipe 2A is provided in a freeze pipe 1 (casing), as shown in FIG. 3, a bottom socket 3 (plugging member) is brazed on the bottom (underground end) of the first coolant circulation pipe 2A (micro channel). The connection between the first coolant circulation pipe 2A and the bottom socket 3, however, may be carried out by means of a non-brazing method.

[0102] In FIG. 3, micro-coolant passages 2Aδ-G provided on the left side in the first coolant circulation pipe 2A (5 micro-coolant passages provided on the left side out of 10 micro-coolant passages 2Aδ in FIG. 3) correspond to a coolant supply side, and micro-coolant passages 2Aδ-R provided on the right side (5 micro-coolant passages provided on the right side out of 10 micro-coolant passages 2Aδ) correspond to a coolant return side that returns to a coolant apparatus 10 (FIG. 1).

[0103] In FIG. 3, the micro-coolant passages 2Aδ-G provided on the left side and the micro-coolant passages 2Aδ-R provided on the right side are communicated each other by the bottom socket 3. In other words, in the first embodiment, one first coolant circulation pipe 2A (micro channel) comprises pipes on a coolant supply side and pipes on a coolant return side.

[0104] In FIG. 3, the bottom socket 3 is provided with a communicating portion 2Aδ-C for communicating the micro-coolant passages 2Aδ-G on the coolant supply side with the micro-coolant passages 2Aδ-R on the coolant return side.

[0105] The liquid-phase carbon dioxide (secondary coolant) supplied from the coolant supply side (e.g. on the ground) flows in the micro-coolant passages 2Aδ-G on the coolant supply side (arrow G), passes through the communicating portion 2Aδ-C in the bottom socket 3 (arrow C), flows in the micro-coolant passages 2Aδ-R on the coolant return side (arrow R), and returns to the coolant apparatus 10 (FIG. 1). Numeral 4D in FIG. 3 indicates a dividing wall which is provided so that a coolant on the coolant supply side and a coolant on the coolant return side are not mixed.

[0106] A top socket 4 (connecting member) is brazed to the above-ground side of a first coolant circulation pipe 2A (micro channel). The connection between the first coolant circulation pipe 2A and the top socket 4, however, may be carried out by means of a non-brazing method.

[0107] The micro-coolant passages 2Aδ-G on the coolant supply side and the micro-coolant passage 2Aδ-R on the coolant return side of the first coolant circulation pipe 2A are connected by the top socket 4 with a coolant supply side and a coolant return side of coolant circulation pipes 2B (second coolant circulation pipes), respectively, a cross-section of which are circular cross-section. The supply side and the return side of the coolant circulation pipes 2B with a circular cross-section are connected with a coolant supply side and a coolant return side (cooling side) of a coolant apparatus 10 (FIG. 1) of liquid-phase carbon dioxide, respectively.

[0108] The constructions of the partly freeze pipe structure of the first embodiment are shown in FIGS. 4 and 5.

[0109] In FIGS. 4 and 5, the system is constructed so as to freeze a lower region from a packer 7 in the ground G merely, and not freeze upper region from the packer 7 in the ground G.

[0110] In FIGS. 4 and 5, in order to inhibit heat exchange between the liquid-phase carbon dioxide in the second coolant circulation pipes 2B (pipes with a circular cross-section) extending in a non-frozen region of the ground G and the ground region being above the packer 7, an insulator 6 is filled in a space between the second coolant circulation pipes 2B (pipes with a circular cross-section) and a casing 1 (freeze pipe). Then, the packer 7 is preferably made of an insulator.

[0111] Herein, a diameter of the second coolant circulation pipes 2B is set to be small enough so as to keep (ensure) a space for filling the insulator 6. Subsequently, the insulator 6 (e.g., urethane foam, styrene foam) is filled from the bottom of the casing 1 through a filling pipe (not shown) so as to be filled in a space between the second coolant circulation pipes 2B and the casing 1.

[0112] On the other hand, to efficiently perform heat exchange between the liquid-phase carbon dioxide in the first coolant circulation pipe 2A (micro channel) extending in a region of the ground G to be frozen and the ground G of the lower region from the packer 7, a heat transfer fluid 5 is filled in a space between the first coolant circulation pipe 2A and the casing 1. The heat transfer fluid 5 is preferably excellent in heat transfer, but may be easily available tap water.

[0113] In the embodiment shown in FIGS. 4 and 5, a space is sufficiently provided between the flat first coolant circulation pipe 2A (micro channel) and the casing 1 in which the heat transfer fluid 5 is filled.

[0114] Herein, in a case that the insulator 6 is a fluid, in order to mix the insulator 6 (fluid) and the heat transfer fluid 5, it is necessary to divide a region of the ground to be frozen and a region of the ground not to be frozen inside of the casing 1 in a fluid-tight manner, by means of the packer 7 which is located and expanded at an area between a region to be frozen and a region not to be frozen.

[0115] On the other hand, when the insulator 6 is a cloth (or flexible and flat) member, the cloth insulator 6 is wound onto the second coolant circulation pipes 2B to reduce heat exchange between the liquid-phase carbon dioxide in the second coolant circulation pipes 2B and the ground. After the cloth insulator 6 is wound onto the second coolant circulation pipes 2B to be fixed (The state that the cloth insulator 6 is wound is not shown), the heat transfer fluid 5 is filled. In a case that a cloth insulator 6 is used, since there is not possibility for generating a situation that the insulator 6 and the heat transfer fluid 5 are mixed, the packer 7 is not necessary.

[0116] In ground freezing work, a casing 1 of a freeze pipe is provided in a borehole drilled for placing freeze pipes to retain a borehole wall. In this specification, the casing is sometimes referred to as “freeze pipe.”

[0117] In a case that high-pressure water is used as a fluid for cutting or drilling a borehole, means for preventing water infiltration (not shown) is provided, and that the water in the casing 1 must be discharged by means of water discharge apparatus (not shown) such as a pump, it is possible to discharge the water in the casing 1 by means of water discharge means such as a pump, after the casing 1 is provided, the means for preventing water infiltration (not shown) is installed at the tip portion (underground end portion) of the casing 1. After the water is discharged, the first coolant circulation pipe 2A (micro channel) having a bottom socket 3 and a top socket 4, which are brazed on the first coolant circulation pipe 2A, is positioned in the casing 1.

[0118] According to the first embodiment shown in drawings, the first coolant circulation pipe 2A (micro channel) and the second coolant circulation pipes 2B (pipe with a circular cross-section) are used as a coolant circulation pipe 2. Herein, since the first coolant circulation pipe 2A (micro channel) is flat and made of aluminum, it is possible to bend and stretch the first coolant circulation pipe. Consequently, as shown in FIG. 8, a micro channel 2A, the length of which is equivalent to a vertical depth of 100 m of frozen ground to be formed underground, can be prepared by rolling a plugging member 3 and a connecting member 4 at a plant, transported at a construction site and stretched linearly to be directly inserted and provided into a borehole (casing 1).

[0119] The second coolant circulation pipes 2B (pipe with a circular cross-section) are small in diameter, it is possible to connect the second coolant circulation pipes 2B of certain length each other by means of a screw pipe-type joint, etc. Likewise, the second coolant circulation pipes 2B with a circular cross-section and the top socket 4 can be joined with a screw pipe-type joint, etc. Accordingly, the second coolant circulation pipes 2B can be connected with the first coolant circulation pipe 2A (micro channel) through the top socket 4 provided in the borehole (casing 1).

[0120] Insertion of the first coolant circulation pipe 2A (micro channel) into a freeze pipe requires no repeated welding of pipes of fixed length (different from double pipes as a prior art brine method).

[0121] By means of a construction without repeating welding of pipes of fixed length, in the first embodiment, constructional costs can significantly be reduced and leakage of a secondary coolant from welded pipes at a site is prevented.

[0122] No welding of first coolant circulation pipes 2A of fixed length (micro channel) can reduce effort for installing each freeze pipe. Moreover, both a first coolant circulation pipe 2A (micro channel) and second coolant circulation pipes 2B (pipes with a circular cross-section) are small in cross-section, enabling the diameter of the casing 1 (freeze pipe) to be smaller, and the construction efficiency and the construction period to be higher and shorter, respectively. Consequently, the horizontal interval between the freeze pipe and the connecting pipe can be reduced and the speed of freezing can be increased more preferably than a prior art brine method. By these advantages, a frozen wall can be formed within a short period of time.

[0123] According to the first embodiment having high construction efficiency, the horizontal interval between freeze pipes can be reduced and thermal conductive properties of cold energy in the ground can be improved.

[0124] Additionally, according to the first embodiment shown, since the heat transfer fluid 5 is filled in a region in the freeze pipe 1 corresponding to a region of the ground to be frozen, and an insulator 6 is provided in a region corresponding to a region of the ground not to be frozen, it is possible to freeze merely the ground to be frozen efficiently.

[0125] Although not shown in FIGS. 3 to 5, a plurality of first coolant circulation pipes 2A (micro channel) can be inserted into the freeze pipe. Accordingly, the flow rate of a coolant (carbon dioxide) can be increased and the method of freezing the ground can efficiently be implemented.

[0126] In the first embodiment shown in FIGS. 1 to 5, first coolant circulation pipes 2A (micro channel) are extended in parallel with the freeze pipe 1. As shown in FIG. 15, however, first coolant circulation pipes 2A can spirally be extended.

[0127] BY means of extending first coolant circulation pipes 2A spirally, a distance of a coolant (carbon dioxide) flowing in a first coolant circulation pipe 2A is long and the efficiency of discharging cold energy retained in the coolant into the soil is improved.

[0128] Other constructions and effects in an alternative embodiment in FIG. 15 are the same as in the first embodiment shown in FIGS. 1 to 5.

[0129] Herein, the bottom socket (plugging member) is not restricted to the embodiment shown in FIG. 3. One example shown in FIG. 17 is that the width of the bottom socket 3A (plugging member) (in horizontal direction in FIG. 17) is determined at the same as that of the first coolant circulation pipe 2A (micro channel) to eliminate lateral bulge in the bottom socket 3A (in horizontal direction in FIG. 17) for achieving easier pipe insertion.

[0130] As shown in FIG. 18, a “lid”-shaped bottom socket 3B (plugging member) can be provided at an underground end (lower end in FIG. 18) of the first coolant circulation pipe 2A (micro channel). Specifically, to provide a communicating portion 2Aδ-C, both edges 2AE of the first coolant circulation pipe 2A (micro channel) vertically extend longer than partition walls 2A-F toward an underground end (lower side in FIG. 18) by a predetermined dimension (dimension necessary to secure the vertical length of the communicating portion 2Aδ-C). By forming a lid-shaped bottom socket 3A (plugging member), the bottom socket 3A can easily and assuredly be connected with the first coolant circulation pipe 2A (micro channel).

[0131] Other constructions of the bottom sockets 3A, 3B (plugging member) shown in FIGS. 17 and 18 are the same as in the embodiment in FIG. 3.

[0132] The top socket (connecting member) is not restricted to the embodiment shown in FIG. 3, as with the bottom socket (plugging member).

[0133] The width of the top socket 4A (connecting member) shown in FIG. 19 (in horizontal direction in FIG. 19) is the same as the width of the first coolant circulation pipe 2A (micro channel), and the extended portion of the top socket 4A is not wider than the first coolant circulation pipe 2A (in horizontal direction in FIG. 19). Accordingly, the socket 4A can be easily inserted into the first coolant circulation pipe 2A.

[0134] In FIG. 19, numeral 4D refers to a dividing wall, and the dividing wall 4D divides a coolant for flowing in a micro-coolant passage 2Aδ-G on a coolant supply side and a coolant for flowing in a micro-coolant passage 2Aδ-R on a coolant return side to prevent from mixing.

[0135] The bottom socket 3B (plugging member) shown in FIG. 20 is provided as a “lid”-shaped member on a coolant supply side (upper end in FIG. 20) of the first coolant circulation pipe 2A (micro channel).

[0136] Also, in this case, both edges 2AE of the first coolant circulation pipe 2A (micro channel) are projected vertically in comparison with partition walls 2A-F in a direction toward an end on a coolant supply side (upward direction in FIG. 18) by a predetermined dimension, a space is formed for communicating the second coolant circulation pipe 2B on the coolant supply side and a micro-coolant passage 2Aδ-G on the coolant supply side, and a space is formed for communicating the micro-coolant passage 2Aδ-G on the coolant return side and the second coolant circulation pipe 2B on the coolant return side. A dividing wall 4D is also prepared.

[0137] By forming a lid-shaped top socket 4A (connecting member), the socket 4A can be connected with a first coolant circulation pipe 2A (micro channel) easily and surely.

[0138] Other constructions of the top sockets 4A, 4B (connecting member) in the FIGS. 19 and 20 are the same as the embodiment in in FIG. 3.

[0139] Herein, a dividing wall 4D is fixed on the top socket 4 shown in FIG. 3, the top socket 4A shown in FIG. 19 and the top socket 4B shown in FIG. 20. However, a dividing wall 4D-A is moveably formed on a top socket 4C shown in FIG. 21 in arrow H direction. This means that the dividing wall 4D may be fixed on the top sockets 4, 4A, and 4B (connecting member), or may be movable as the dividing wall 4D-A on the top socket 4C shown in FIG. 21 (connecting member).

[0140] Although not clearly shown in FIG. 21, the dividing wall 4D-A moves along a top wall 4T of the top socket 4C in arrow H direction. This construction for moving the dividing wall 4D-A n the arrow H direction can be provided by a known structure including a rack and a pinion, with an electric motor (not shown) as a power source.

[0141] A second embodiment of the present invention will be described with reference to FIGS. 6 to 9.

[0142] In the first embodiment shown in FIGS. 3 to 5, a first coolant circulation pipe 2A, composed of micro-coolant passages, is provided only near the bottom in a freeze pipe 1 (casing), and second coolant circulation pipes 2B (pipes with a circular cross-section) connected with the first coolant circulation pipe 2A through a top socket 4 (connecting member) are also inserted into the freeze pipe 1 (casing).

[0143] On the other hand, in the second embodiment, the first coolant circulation pipe 2A (micro channel) is inserted into a freeze pipe 1 (casing) throughout a vertical direction area (in vertical direction in FIG. 6) corresponding to the freeze pipe 1, while second coolant circulation pipes 2B with a circular cross-section are not inserted into the freeze pipe 1 (casing).

[0144] In FIG. 6, the first coolant circulation pipe 2A (micro channel) is provided along the freeze pipe 1 (casing) vertically.

[0145] In the first coolant circulation pipe 2A (micro channel), micro-coolant passages 2Aδ-G on the left side (5 micro-coolant passages on the left side in FIG. 6 in 10 micro-coolant passages 2Aδ shown in FIG. 2) correspond to a coolant supply side (arrow G), and micro-coolant passages 2Aδ-R in the right side region (5 micro-coolant passages on the right side in FIG. 6 in 10 micro-coolant passages 2Aδ shown in FIG. 2) correspond to a coolant return side (arrow R) that returns to a coolant apparatus 10 (FIG. 1). FIGS. 6 and 7 show micro-coolant passages 2Aδ-G on a coolant supply side from the ground and micro-coolant passages 2Aδ-R on a coolant return side that returns to the ground, each composed of 5 micro-coolant passages 2Aδ.

[0146] In FIG. 6, on the ground being above the freeze pipe 1 (casing), the top of the first coolant circulation pipe 2A (micro channel) is connected with the top socket 4 and the socket is connected with the second coolant circulation pipes 2B (pipe with a circular cross-section), the coolant supply side of the first coolant circulation pipe 2A is connected with the coolant supply side of the second coolant circulation pipe 2B, and also, the coolant return side of the first coolant circulation pipe 2A is connected with the coolant return side of the second coolant circulation pipe 2B.

[0147] The coolant circulation pipes 2B with a circular cross-section are connected with the coolant supply side and the coolant return side (cooling side) of the coolant apparatus 10 (FIG. 1) of liquid-phase carbon dioxide. This means that the construction of the freezing system on the ground in FIG. 6 is the same as the construction where the top of the coolant circulation pipe 2A (micro channel) is connected with the top socket 4 in the first embodiment shown in FIG. 3.

[0148] In the second embodiment, the first coolant circulation pipe 2A can also spirally be extended (FIG. 15).

[0149] As shown in FIG. 7, at the lower portion of the first coolant circulation pipe 2A (micro channel), a bottom socket 3 (plugging member) is brazed on the bottom of the first coolant circulation pipe 2A, as shown in FIG. 3 (as the first embodiment), so that the micro-coolant passages 2Aδ-G on the coolant supply side are communicated with the micro-coolant passages 2Aδ-R on the coolant return side through the bottom socket 3, and the communicating portion 2Aδ-C is formed.

[0150] The freezing system according to the second embodiment, as shown in FIG. 6, provides the partly freeze pipes structures of a partial freeze pipe for freezing merely a partial region of a ground G.

[0151] In FIG. 6, as described in reference with FIGS. 4 and 5, the region of the ground to be frozen is an area below the packer 7, and therefore, the heat transfer fluid 5 is filled in a space between the first coolant circulation pipe 2A (micro channel) extending in a region below the packer 7 and the casing 1.

[0152] On the other hand, a region of the ground not to be frozen is an area above the packer 7, and therefore, an insulator 6 is filled in a space between the first coolant circulation pipe 2A (micro channel) extending in a region above the packer 7 and the casing 1 (freeze pipe).

[0153] Further, FIG. 6 shows a case that the insulator 6 is a fluid, and the region of the ground to be frozen and the region of the ground not to be frozen are divided in fluid-tight manner by expanding the packer 7. This construction is carried out in order to prevent mixture of the fluid insulator 6 and the heat transfer fluid 5.

[0154] On the other hand, in a case that the insulator 6 is made of cloth (flexible plate-shaped body) and is wound onto the first coolant circulation pipe 2A (micro channel) in order to control heat exchange between the liquid-phase carbon dioxide as a coolant and the ground, since the insulator 6 and the heat transfer fluid 5 are not mixed, it is not necessary to provide the packer 7.

[0155] In a prior art brine method, a freeze pipe buried in the ground is constructed as a double-pipe in order to comprise a supply side path and a return side path of brine (secondary coolant). On the other hand, in the second embodiment shown in the drawings, since one of the first coolant circulation pipe 2A (micro channel) can be inserted into the hollow circular pipe casing 1, the coolant pipes can be easily provided and the work efficiency can be improved extremely.

[0156] Also, as like as the first embodiment, since the first coolant circulation pipe 2A (micro channel) is shaped in flat manner and made of aluminum, it is possible to bend and stretch the first coolant circulation pipe 2A. Accordingly, as shown in FIG. 8, a micro channel for the first coolant circulation pipe 2A, the length of which corresponds to a vertical depth of 100 m of frozen ground to be formed underground, is connected with a plugging member 3 and a connecting member 4 by brazing, is rolled at a plant, is transported at a construction site, is stretched linearly by a micro channel rolling machine 9 to be directly inserted, and is provided into a borehole (freeze pipe 1). Consequently, welding of double pipes of fixed length, which is required in a prior art brine method, is not required, and therefore, construction work of providing the coolant pipes is significantly reduced. Also, potential leakage of the secondary coolant from portions being welded at the construction site is prevented.

[0157] As shown in FIG. 8, in a case that two or more micro channels 2A (first coolant circulation pipes) are buried (buried) in the ground, it is preferable that a spacer 8 for horizontally holding each of the micro channels 2A is provided, in order to carry out smooth insertion of a plurality of micro channels 2A into a single borehole (freeze pipe 1), to prevent a contact of a plurality of micro channels 2A each other after said insertion, to prevent a contact of the micro channels 2A with an inner wall of the borehole (freeze pipe 1), and more advantageously, to keep an appropriate horizontal interval of the plurality of micro channels 2A each other.

[0158] The spacer 8, as shown in FIG. 8, is provided so as to make a space between a plurality of micro channels (first coolant circulation pipes 2A).

[0159] Typical shapes of the spacer 8 are shown in FIG. 9 (1), FIG. 9(2), and FIG. 9(3).

[0160] Since the shape of the spacer 8 varies according to the number of micro channels (the first coolant circulation pipes 2A) to be inserted into the borehole (freeze pipe 1), a spacer with numeral 8A shown in FIG. 9(1) is used in a case that two micro channels 2A should be inserted into the borehole, a spacer with numeral 8B shown in FIG. 9(2) is used in a case that three micro channels 2A should be inserted into the borehole, and a spacer with numeral 8C shown in FIG. 9(3) is used in a case that four micro channels 2A should be inserted into the borehole.

[0161] In order to insert the micro channels 2A into a borehole (freeze pipe 1) and to fill the heat transfer fluid 5 after insert of the micro channel 2A, a plurality of openings 8M are formed so as to pass the micro channel 2A there-through and openings 8H (hatched) are formed so as to fill the heat transfer fluid 5 there-through, the openings 8M and 8H are formed in spacers 8A to 8C shown in FIG. 9(1), FIG. 9 (2), and FIG. 9(3) respectively.

[0162] The spacer 8 is preferably made of metal excellent in heat transfer, but may be made of easily available inexpensive plastics.

[0163] In addition, the above-mentioned spacers 8 can be employed in the first embodiment.

[0164] The second embodiment includes the applications to radially outwardly provided freeze pipes in tunnels and horizontal freeze pipes in shafts.

[0165] Other constructions and effects of the second embodiment shown in FIGS. 6 to 9 are the same as in the first embodiment shown in FIGS. 3 to 5.

[0166] An alternative embodiment of the first embodiment and the second embodiment shown in FIGS. 3 to 9 is shown in FIG. 10. In FIG. 10, a plurality of coolant circulation pipes 2A1 as shown in FIGS. 3 to 9 are inserted into a freeze pipe 1.

[0167] In FIG. 10, 8 micro-coolant passages 2Aδ are formed inside of a flat coolant circulation pipe 2A1, having a female tenon 2F at one end and a male tenon 2M at the other end. A female tenon 2F of one coolant circulation pipe 2A1 and a male tenon 2M of its neighboring coolant circulation pipe 2A1 are engaged with each other to be arranged.

[0168] In FIG. 10, 6 flat coolant circulation pipes 2A1 are provided in the freeze pipe 1 in an overall hexagonal form.

[0169] An assembly jig 22 of a substantially hexagonal form is provided radially inwardly from 6 coolant circulation pipes 2A1 of an overall hexagonal form. The assembly jig 22 includes protrusions 24 each of which protrudes outwardly in radial direction. By engaging the protrusions 24 with positioning grooves 2G each of which recesses inwardly in radial direction from a coolant circulation pipe 2A1, the positions of the 6 coolant circulation pipes 2A1 are determined relative to the assembly jig 22. Accordingly, the assembly jig 22 and the 6 coolant circulation pipes 2A1 are integrally bundled by means of a cable tie 26.

[0170] The arrangement shown in FIG. 10 enables a plurality of coolant circulation pipes 2A1 to uniformly be provided in the freeze pipe 1 and the ground outside of the freeze pipe 1 to be efficiently cooled by carbon dioxide (coolant) flowing in a plurality of coolant circulation pipes 2A1.

[0171] Other constructions and effects of an alternative embodiment shown in FIG. 10 are the same as in the first embodiment and the second embodiment shown in FIGS. 3 to 9.

[0172] A third embodiment of the present invention will be described with reference to FIGS. 11 to 14.

[0173] In FIG. 11, a coolant circulation pipe (micro channel) used in the third embodiment is denoted as numeral “3C.” The coolant circulation pipe 3C is entirely formed of a hollow cylinder (pipe), and a plurality of micro-coolant passages 3Cδ-G (8 micro-coolant passages in FIG. 11) are formed in a radially outwardly located region. A radially inwardly located hollow portion 3Cδ-R constructs a coolant return path for returning a coolant to a coolant apparatus 10 (shown in FIG. 1), and also, an internal diameter of the radially inwardly located hollow portion 3Cδ-R is set so as to be larger than an internal diameter of a micro-coolant passages 3C δ-G.

[0174] The hollow portion of the coolant circulation pipe 3C may be written by phrases “a coolant return path 3Cδ-R” or “a coolant path 3C—5-R”. As mentioned above, a coolant circulation pipe 3C, in the form of hollow cylinder (pipe), may herein be denoted as “micro channel,” as shown in FIGS. 11 to 14.

[0175] In FIG. 12, a bottom socket 33 (plugging member) is brazed on the bottom of a first coolant circulation pipe 3C (micro channel) (underground end: lower portion in FIG. 12). This connection, however, may be achieved by a non-brazing method.

[0176] As mentioned above with reference to FIG. 11, a plurality of micro-coolant passages 3Cδ-G formed in a region radially outwardly located in the first coolant circulation pipe 3C in FIG. 12 correspond to a coolant supply side, and a coolant path 3Cδ-R formed in a region radially inwardly located in the first coolant circulation pipe 3C correspond to a coolant return side that returns to the coolant apparatus 10 (FIG. 1).

[0177] In FIG. 12, a micro-coolant passages 3Cδ-G in a radially outwardly located region and a coolant path 3Cδ-R in a radially inwardly located region are communicated by the bottom socket 33. Accordingly, the system according to the third embodiment, as in the first embodiment, also includes one first coolant circulation pipe 3C (micro channel), composed of a coolant supply side and a coolant return side.

[0178] In FIG. 12, the bottom socket 33 is provided with a communicating portion 3Cδ-C for communicating a micro-coolant passages 3Cδ-G on a coolant supply side and a coolant path 3Cδ-R on a coolant return side.

[0179] The liquid-phase carbon dioxide (secondary coolant) supplied from the coolant supply side flows in a plurality of micro-coolant passages 3Cδ-G on a coolant supply side (arrow G) to pass through the communicating portion 3Cδ-C in the bottom socket 33 (arrow C), the coolant paths 3Cδ-R on the coolant return side (arrow R) and return to the coolant apparatus 10 (FIG. 1).

[0180] The top socket 34 (connecting member) is brazed on the ground side of the first coolant circulation pipe 3C (micro channel) (upper portion in FIG. 12). However, as the bottom socket 33, this connection may be achieved by a non-brazing method.

[0181] In FIG. 12, a micro-coolant passages 3Cδ-G on a coolant supply side of the first coolant circulation pipe 3C is connected with a coolant supply side (coolant circulation pipe 2B on the left side in FIG. 12) of a coolant circulation pipe 2B with a circular cross-section (second coolant circulation pipe) through a coolant supply path 34I, in the top socket 34. On the other hand, a coolant path 3Cδ-R on a coolant return side of the first coolant circulation pipe 3C is connected with a coolant return side (coolant circulation pipe 2B on the right side in FIG. 12) of the coolant circulation pipe 2B with a circular cross-section (second coolant circulation pipe) through a coolant supply path 340 in the top socket 34.

[0182] The supply side and the return side of the coolant circulation pipes 2B with a circular cross-section are connected with a coolant supply side and a coolant return side (cooling line) of the coolant apparatus 10 (FIG. 1) of liquid-phase carbon dioxide, respectively.

[0183] According to the third embodiment being explained in reference with FIGS. 11 and 12, a coolant supply path in the first coolant circulation pipe 3C corresponds to a plurality of micro-coolant passages 3Cδ-G which are formed in a radially outwardly located region, and all the micro-coolant passages 3Cδ-G formed in the first coolant circulation pipe 3C can be used (applied) as a coolant supply path to cool the ground efficiently.

[0184] On the other hand, when a coolant having cooled the ground and having absorbed underground heat returns to the coolant apparatus 10 (FIG. 1), since said coolant flows in the radially inwardly located coolant path 3Cδ-R with a relatively large diameter, a ratio of flow area relative to flow rate relating to the radially inwardly located coolant path is smaller than the coolant supply path 3Cδ-G, and therefore, it is a low degree of possibility that a heat of the coolant flowing in the return path is transmitted to the coolant flowing in the micro-coolant passages 3Cδ-G.

[0185] FIG. 13 shows one example of first coolant circulation pipes used in the third embodiment, and both ends of a first coolant circulation pipe 3C1 shown in FIG. 13 are complementary in shape to other ends. When the first coolant circulation pipes 3C1 shown in FIG. 13 are connected, ends having complementary shapes are engaged with each other to be fixed by a pipe fixing member 42.

[0186] In FIG. 13, numeral 44 refers to a seal member for preventing leakage of a coolant (e.g., O-ring).

[0187] However, the connection of the first coolant circulation pipes used in the third embodiment is not restricted to the embodiment shown in FIG. 13.

[0188] As shown in FIG. 14, an opening 50 of an upper end of one first coolant circulation pipe 3C21 (coolant circulation pipe 3C2 in lower portion in FIG. 14) can be constructed to receive a lower end of the other first coolant circulation pipe 3C22 (coolant circulation pipe 3C2 in upper portion in FIG. 14) for connection.

[0189] In order to prevent leakage of a coolant (carbon dioxide) from a connected portion, as shown in FIG. 14, a concave 52 (groove) extending circumferentially is formed on the outer peripheral surface of the upper first coolant circulation pipe 3C22, and a convex 56 made of sealing material (or O-ring) is formed in an opening 50 of a lower first coolant circulation pipe 3C21. When the first coolant circulation pipes 3C21, 3C22 are connected with each other, the convex 56 (sealing material) is engaged with the concave 50 to prevent leakage of a coolant (carbon dioxide) from a connected portion of the first coolant circulation pipes 3C21, 3C22.

[0190] Other constructions and effects in the third embodiment shown in FIGS. 11 to 14 are the same as in the embodiment shown in FIGS. 1 to 10.

[0191] Although the invention has been described through its specific form, it is to be understood that the described embodiment is only illustrative and is not intended to limit the scope of the invention.

[0192] In the embodiment shown herein, a borehole for inserting a freeze pipe is drilled using a casing drilling unit, but a borehole may be drilled by other methods (e.g., muddy water drilling method).

[0193] In the embodiments shown herein, a region extending vertically in the ground is frozen. However, in the present invention, a region horizontally extending in the ground and a region extending aslant from the vertical direction in the ground can be frozen.

[0194] In the embodiments shown herein, a region in the ground extending vertically downwardly from the ground is frozen. However, in the present invention, a region in the ground extending vertically upwardly can be frozen.

EXPLANATION OF LETTERS AND NUMERALS

[0195] 1 . . . Freeze pipe (casing) [0196] 2 . . . Coolant circulation pipe [0197] 2A, 3C, 3C1, 3C21, 3C22 . . . First coolant circulation pipe (micro channel) [0198] 2Aδ-G, 2Aδ-R, 3Cδ-G . . . Micro-coolant passage of first coolant circulation pipe [0199] 2B . . . Second coolant circulation pipe (coolant circulation pipe with circular cross-section) [0200] 3, 3A, 3B, 33 . . . Plugging member (bottom socket) [0201] 4, 4A, 4B, 4C, 34 . . . Connecting member (top socket) [0202] 5 . . . Heat transfer fluid [0203] 6 . . . Insulator [0204] 7 . . . Packer [0205] 8 . . . Spacer [0206] 8H, 8M . . . Opening of spacer [0207] 9 . . . Micro channel rolling machine [0208] 10 . . . Coolant apparatus [0209] 10A . . . Liquefier [0210] 10B . . . Condenser [0211] 10C . . . Cooling tower [0212] 11 . . . Coolant circulation pump [0213] 100 . . . refrigerator [0214] 100A . . . Evaporator [0215] 100B . . . Condenser [0216] 100C . . . Cooling tower [0217] 101 . . . Freeze pipe [0218] 102 . . . Coolant circulation pump