CO2 transcritical freezing system and freezing method

Abstract

The invention relates to the technical field of deep underground space stratum reinforcement, in particular to a CO2 transcritical freezing system and method.The CO2 transcritical freezing system comprises a freezing subsystem which comprises a first liquid inlet pipe and a first liquid return pipe which are arranged above a stratum and used for conveying low-temperature liquid CO2 to the stratum to conduct stratum freezing construction; the liquefaction subsystem is used for compressing the volume of the normal-temperature gaseous CO2, so that the movement of molecules in the gaseous CO2 is limited and reduced, and the gaseous CO2 is converted into low-temperature liquid CO2; and an inlet and return pipeline subsystem. The CO2 medium adopted by the invention effectively solves the problems of flammability, explosiveness, high risk, difficulty in treatment, environmental pollution and the like caused by liquid ammonia and saline water utilized in the traditional freezing construction; and a water-bearing layer, a soft stratum and the like are frozen and reinforced through compressed and converted low-temperature liquid CO2, a water-resisting layer and a temporary support are formed, seepage of water and sinking, displacement and collapse of the wall face and the bottom plate are effectively prevented, and the stability of the frozen area to be excavated is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of deep underground space stratum reinforcement, in particular to the field of freezing construction of deep underground spaces and wellbores passing through aquifers, soft soil, soft rocks, broken zones and other unfavorable strata, and specifically to a CO2 transcritical freezing system and freezing method. Background Art

[0002] With the continuous and rapid development of the economy and society, the development and utilization of deep underground space in cities and the exploitation of deep mineral resources will face adverse and complex geological conditions such as groundwater, soft soil, soft rock, and broken zones.

[0003] At present, various traditional pile foundation construction methods are widely used, but they are costly and have risks and defects in waterproofing. There is also the traditional freezing method construction. The current technology uses liquid ammonia and brine as the medium and refrigerant. Because the liquid ammonia used is flammable and explosive, the safety risk is high. A large amount of brine is difficult to handle and pollutes the environment. As a result, the above-mentioned freezing method construction has certain defects in actual construction and cannot meet the requirements of safety, efficiency and environmental protection.

[0004] The above contents are only used to assist in understanding the technical solution of the present invention, and do not constitute an admission that the above contents are the closest prior art. Summary of the invention

[0005] The object of the present invention is to solve the above-mentioned deficiencies and provide a CO2 transcritical freezing system and freezing method.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solution: a CO2 transcritical freezing system, comprising:

[0007] The freezing subsystem includes a first liquid inlet pipe and a first liquid return pipe arranged above the formation, and is used to transport low-temperature liquid CO2 to the formation for formation freezing construction;

[0008] The liquefaction subsystem is used to compress the volume of gaseous CO2 at room temperature so that the movement of molecules in the gaseous CO2 is restricted and reduced, and then converted into low-temperature liquid CO2;

[0009] The inlet and return pipeline subsystem is used to carry out liquid return circulation of the low-temperature liquid CO2 transported by the freezing subsystem.

[0010] Furthermore, the freezing subsystem further includes:

[0011] A liquid inlet branch pipe, located at the lower part of the first liquid inlet pipe and evenly provided with a plurality of branches, for being inserted into the formation;

[0012] The liquid return branch pipe is located at the lower part of the first liquid return pipe and is evenly provided with a plurality of them, and is sleeved on the outside of the liquid inlet branch pipe at intervals.

[0013] Furthermore, the liquefaction subsystem includes:

[0014] Storage tanks are used as closed containers for storing gaseous CO2;

[0015] A compressor, used to compress the volume of gaseous CO2 inside the storage tank and convert it into cryogenic liquid CO2;

[0016] The conduit is arranged between the storage tank and the compressor, and is used for evenly distributing and transporting the gaseous CO2 filled in the storage tank to the compressor.

[0017] Furthermore, the inlet and return piping subsystem includes:

[0018] A second liquid inlet pipe is provided between the first liquid inlet pipe and the compressor, and is used to transport the low-temperature liquid CO2 compressed and converted by the compressor to the formation;

[0019] A second liquid return pipe, connected to the first liquid return pipe and disposed on the compressor, for returning the liquid CO2 entering the formation into the compressor;

[0020] The booster pump station is arranged on the delivery pipeline of the second liquid inlet pipe, and is used to provide power for delivering liquid CO2 to the first liquid inlet pipe.

[0021] Furthermore, a channel penetrating from top to bottom is correspondingly arranged outside the liquid return branch pipe and on the stratum, and the liquid return branch pipe is accommodated inside the channel.

[0022] A CO2 transcritical freezing method, used in the CO2 transcritical freezing system, comprises the following steps:

[0023] S1, determine the construction location:

[0024] According to the hydrogeological conditions of the deep underground space and the wellbore to be constructed, the area to be frozen around the deep underground space and the wellbore shall be planned and determined;

[0025] S2, hole making construction:

[0026] Use deep drilling to open multiple channels with equal spacing around the planned area to be frozen;

[0027] S3, freeze equipment layout:

[0028] A conduit is connected between the storage tank and the compressor, and then a second liquid inlet pipe and a second liquid return pipe with a pressurizing pump station are respectively connected to the compressor, wherein the second liquid inlet pipe is connected to the first liquid inlet pipe, and the second liquid return pipe is connected to the first liquid return pipe;

[0029] S4, freeze construction:

[0030] Multiple liquid return branch pipes welded to the first liquid return pipe are sequentially lowered into the opened multiple channels, and then a liquid inlet branch pipe welded to the first liquid inlet pipe is installed inside each liquid return branch pipe. The pressure pump station is turned on to transport low-temperature liquid CO2 into the channel to freeze the poor strata around the area to be frozen to form a frozen wall, thereby ensuring that subsequent excavation construction in the area to be frozen proceeds normally.

[0031] Furthermore, the deep drilling method implemented in step S2 uses a drilling rig as the equipment.

[0032] Furthermore, in the deep drilling method in step S2, the equipment is calibrated every 5-10 m of drilling.

[0033] Furthermore, the plane shape planned on the area to be frozen in step S2 is consistent with the plane shape formed by the multiple channels with deep holes around it.

[0034] Furthermore, the difference between the cross-sections of the liquid return branch pipe and the liquid inlet branch pipe used in step S4 is greater than the cross-sectional area of ​​the liquid inlet branch pipe.

[0035] Compared with the prior art, the present invention has the following beneficial effects: the CO2 medium adopted in the present invention effectively solves the problems of flammability, explosion, high risk, difficulty in handling, and environmental pollution brought about by liquid ammonia and brine used in traditional freezing construction, and meets the requirements of safety, high efficiency and environmental protection; the low-temperature liquid CO2 converted by compression is also used to freeze and reinforce aquifers, soft strata, etc., to form a waterproof layer and temporary support, effectively preventing water seepage and sinking, displacement, and collapse of walls and bottom plates, improving the stability of the frozen area to be excavated, and reducing and avoiding the risks and defects in waterproofing that may occur in other traditional pile foundation construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0037] Figure 1 A schematic diagram of a multi-subsystem distribution structure according to an embodiment of the present invention;

[0038] Figure 2 It is a schematic diagram of the planar layout structure of an embodiment of the present invention;

[0039] Figure 3 It is a schematic diagram of the facade layout structure of an embodiment of the present invention;

[0040] Figure 4 for Figure 3 Enlarged structural diagram at point A in the middle.

[0041] In the figure: 1. Freezing subsystem; 11. First liquid inlet pipe; 111. Liquid inlet branch pipe; 12. First liquid return pipe; 121. Liquid return branch pipe; 2. Liquefaction subsystem; 21. Storage tank; 22. Compressor; 23. Conduit; 3. Inlet and return pipeline subsystem; 31. Second liquid inlet pipe; 32. Second liquid return pipe; 33. Pressurizing pump station; 4. Channel. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0043] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0044] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, "multiple" refers to more than two. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0045] like Figure 1-4 As shown, the present invention provides a CO2 transcritical freezing system, comprising:

[0046] The freezing subsystem 1 includes a first liquid inlet pipe 11 and a first liquid return pipe 12 arranged above the formation, and is used to transport low-temperature liquid CO2 to the formation for formation freezing construction;

[0047] Liquefaction subsystem 2 is used to compress the volume of gaseous CO2 at room temperature so that the movement of molecules in the gaseous CO2 is restricted and reduced, and then the gaseous CO2 is converted into low-temperature liquid CO2;

[0048] The inlet and return pipeline subsystem 3 is used for liquid return circulation of the low-temperature liquid CO2 transported by the freezing subsystem 1.

[0049] In a specific implementation, the liquefaction subsystem 2 converts gaseous CO2 at room temperature into high-pressure and low-temperature liquid CO2 at -30° to -50°. By converting different pressures and different states of CO2, the low-temperature liquid CO2 is transported to the target position of the formation through the first liquid inlet pipe 11 and the first liquid return pipe 12 included in the freezing subsystem 1 to freeze, thereby forming a water-proof layer and improving the freezing properties of the formation. The liquid CO2 entering the formation will be transported into the liquefaction subsystem 2 through the return liquid transport of the inlet and return pipeline subsystem 3, forming a circulating transport path, thereby ensuring the utilization rate of the liquid CO2 and minimizing the uneven temperature of the transported liquid CO2.

[0050] The first liquid inlet pipe 11 and the first liquid return pipe 12 included in the freezing subsystem 1 both adopt an annular structure, and the plane shapes of the first liquid inlet pipe 11 and the first liquid return pipe 12 are consistent with the top open shape of the area to be frozen.

[0051] In one embodiment, the freezing subsystem 1 further includes:

[0052] A liquid inlet branch pipe 111, located at the lower part of the first liquid inlet pipe 11 and evenly provided with a plurality of branches, for being inserted into the formation;

[0053] The liquid return branch pipe 121 is located at the lower part of the first liquid return pipe 12 and is evenly provided with a plurality of them, which are sleeved at intervals on the outside of the liquid inlet branch pipe 111. In this design, by uniformly welding a plurality of liquid inlet branches 111 on the lower surface of the first liquid inlet pipe 11, and uniformly welding a plurality of liquid return branches 121 on the lower surface of the first liquid return pipe 12, and sleeve-combining the liquid inlet branches 111 and the liquid return branches 121 corresponding to each other in position, the low-temperature liquid CO2 transported to the formation through the liquid inlet branch pipe 111 freezes the formation, and then the liquid is transported back to the inlet and return pipeline subsystem 3 through the liquid return branch pipe 121, effectively avoiding uneven temperature distribution of the transported liquid CO2.

[0054] It should be noted that the liquid inlet branch pipe 111 and the liquid return branch pipe 121 are both constructed by vertically welding multiple sections of steel pipes. The lengths of the liquid inlet branch pipe 111 and the liquid return branch pipe 121 can be determined according to actual construction conditions to meet construction requirements in multiple construction scenarios.

[0055] In one embodiment, the liquefaction subsystem 2 includes:

[0056] A storage tank 21 is used as a closed container for storing gaseous CO2;

[0057] A compressor 22, used to compress the gaseous CO2 inside the storage tank 21 into low-temperature liquid CO2;

[0058] The conduit 23 is arranged between the storage tank 21 and the compressor 22, and is used to evenly distribute and transport the gaseous CO2 filled in the storage tank 21 to the compressor 22. In this design, the conduit 23 is connected to the storage tank 21 and the compressor 22 at both ends, wherein the storage tank 21 uses more than two rigid closed containers to store gaseous CO2, and a ball valve is provided on the upper part thereof to connect the filling device of gaseous CO2 to ensure sufficient supply of gaseous CO2, and more than three compressors 22 are connected at the lower part thereof through the conduit 23 with a ball valve structure, and the compressor 22 can be used to do work to convert the gaseous CO2 at normal temperature into high-pressure and low-temperature liquid CO2 at -30° to -50°.

[0059] It should be noted that the number of storage tanks 21 and the number of compressors 22 are determined according to actual construction conditions to ensure the conversion capacity of gaseous CO2 into high-pressure and low-temperature liquid CO2.

[0060] In one embodiment, the inlet and return pipeline subsystem 3 includes:

[0061] A second liquid inlet pipe 31 is provided between the first liquid inlet pipe 11 and the compressor 22, and is used to transport the low-temperature liquid CO2 compressed and converted by the compressor 22 to the formation;

[0062] A second liquid return pipe 32, connected to the first liquid return pipe 12 and disposed on the compressor 22, for returning the liquid CO2 entering the formation into the compressor 22;

[0063] The booster pump station 33 is arranged on the delivery pipeline of the second liquid inlet pipe 31, and is used to provide power for delivering liquid CO2 to the first liquid inlet pipe 11. In this design, by welding the second liquid inlet pipe 31 on the first liquid inlet pipe 11, and connecting one end of the second liquid inlet pipe 31 to the liquid outlet end of the compressor 22 through a ball valve, the high-pressure and low-temperature liquid CO2 can be delivered to the first liquid inlet pipe 11 under the action of the booster pump station 33 connected to the second liquid inlet pipe 31, until it enters the formation through the multiple liquid inlet branches 111 welded on the lower surface of the first liquid inlet pipe 11; and by welding the second liquid return pipe 32 on the first liquid return pipe 12, and connecting one end of the second liquid return pipe 32 to the liquid return end of the compressor 22 through a ball valve, the liquid CO2 entering the formation can be circulated and delivered to the compressor 22, thereby achieving a closed circulation delivery effect, and avoiding uneven temperature distribution of the low-temperature liquid CO2 delivered in the formation.

[0064] In one embodiment, a channel 4 is provided on the outside of the liquid return branch pipe 121 and on the ground correspondingly, and the liquid return branch pipe 121 is accommodated in the channel 4. With this design, a rotary drill is used to perform deep drilling operations on the ground and around the area to be frozen, and the depth and diameter of the drilling can fully accommodate the liquid return branch pipe 121. The metal wall surface of the liquid return branch pipe 121 is used for heat exchange, and the soil layer near the channel 4 is frozen to form a frozen wall, achieving the same effect as pile foundation support, and ensuring the subsequent safe construction operation of the area to be frozen.

[0065] A CO2 transcritical freezing method, used in the CO2 transcritical freezing system, comprises the following steps:

[0066] S1, determine the construction location:

[0067] According to the hydrogeological conditions of the deep underground space and the wellbore to be constructed, the deep underground space and the area around the wellbore to be frozen are planned and determined;

[0068] S2, hole making construction:

[0069] A plurality of channels with equal spacing are opened around the planned area to be frozen by deep drilling 4;

[0070] S3, freeze equipment layout:

[0071] A conduit 23 is connected between the storage tank 21 and the compressor 22, and then a second liquid inlet pipe 31 and a second liquid return pipe 32 having a pressurizing pump station 33 are respectively connected to the compressor 22, wherein the second liquid inlet pipe 31 is connected to the first liquid inlet pipe 11, and the second liquid return pipe 32 is connected to the first liquid return pipe 12;

[0072] S4, freeze construction:

[0073] A plurality of liquid return branch pipes 121 welded to the first liquid return pipe 12 are sequentially lowered into the opened plurality of channels 4, and then a liquid inlet branch pipe 111 welded to the first liquid inlet pipe 11 is installed and inserted inside each liquid return branch pipe 121. The booster pump station 33 is turned on to transport low-temperature liquid CO2 into the channel 4 to freeze the poor strata around the area to be frozen to form a frozen wall, thereby ensuring that subsequent excavation construction in the area to be frozen proceeds normally.

[0074] In specific implementation, the CO2 compressor 22 works to convert gaseous CO2 at room temperature into high-pressure, low-temperature liquid CO2 at -30° to -50°. By converting CO2 at different pressures and different states, the low-temperature liquid CO2 is transported to the required frozen stratum, thereby improving the properties of the frozen stratum and meeting the needs of construction.

[0075] In one embodiment, the deep drilling method implemented in step S2 uses a drilling machine, which is suitable for penetrating different types of soils, cutting the soil by rotating the drill bit, and performing deep drilling operations on the strata, and has good operability.

[0076] In one embodiment, the equipment is calibrated every 5-10 m in the deep drilling method in step S2. With this design, the internal deviation is strictly controlled, the over-deviation is corrected in time, and the drilling deviation map is drawn in time. The deviation that does not meet the design requirements must be supplemented to ensure the accuracy of the hole position and depth.

[0077] In one embodiment, the plane shape planned on the area to be frozen in step S2 is consistent with the plane shape formed by the multiple channels 4 with deep holes around it. This design can freeze the surrounding areas in accordance with the plane shape planned on the area to be frozen, avoiding water seepage and displacement, sinking and collapse of the supporting wall in subsequent construction operations, and improving the stability and quality of the area to be frozen.

[0078] In one embodiment, the difference between the cross-sections of the liquid return branch pipe 121 and the liquid inlet branch pipe 111 used in step S4 is greater than the cross-sectional area of ​​the liquid inlet branch pipe 111. With this design, the liquid inlet branch pipe 111 can be sleeved in the liquid return branch pipe 121 and sufficient accommodation space is reserved, ensuring that the incoming liquid CO2 quickly freezes the soil layer near the channel 4, and ensuring the normal liquid return cycle, avoiding uneven temperature of the liquid CO2, improving the freezing efficiency of the liquid CO2, and having a good use effect.

[0079] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A CO2 transcritical freezing system, characterized in that: include: The freezing subsystem (1) comprises a first liquid inlet pipe (11) and a first liquid return pipe (12) arranged above the formation, and is used to transport low-temperature liquid CO2 to the formation for freezing the formation; The liquefaction subsystem (2) is used to compress the volume of gaseous CO2 at room temperature so that the movement of molecules in the gaseous CO2 is restricted and reduced, thereby converting the gaseous CO2 into low-temperature liquid CO2; The inlet and return pipeline subsystem (3) is used to carry out liquid return circulation of the low-temperature liquid CO2 transported by the freezing subsystem (1).

2. A CO2 transcritical freezing system according to claim 1, characterized in that: The freezing subsystem (1) further comprises: A liquid inlet branch pipe (111), located at the lower part of the first liquid inlet pipe (11) and evenly provided with a plurality of branches, for being inserted into the formation; The liquid return branch pipe (121) is located at the lower part of the first liquid return pipe (12) and is evenly provided in plurality and is sleeved at intervals on the outside of the liquid inlet branch pipe (111).

3. A CO2 transcritical freezing system according to claim 1, characterized in that: The liquefaction subsystem (2) comprises: A storage tank (21) is used as a closed container for storing gaseous CO2; A compressor (22) for compressing the volume of gaseous CO2 inside the storage tank (21) to convert it into cryogenic liquid CO2; The conduit (23) is arranged between the storage tank (21) and the compressor (22) and is used to evenly distribute and transport the gaseous CO2 filled in the storage tank (21) to the compressor (22).

4. A CO2 transcritical freezing system according to claim 3, characterized in that: The inlet and return pipeline subsystem (3) comprises: A second liquid inlet pipe (31), arranged between the first liquid inlet pipe (11) and the compressor (22), and used for transporting low-temperature liquid CO2 compressed and converted by the compressor (22) to the formation; a second liquid return pipe (32), connected to the first liquid return pipe (12) and arranged on the compressor (22), for returning the liquid CO2 entering the formation into the compressor (22); The pressure pump station (33) is arranged on the delivery pipeline of the second liquid inlet pipe (31) and is used to provide power for delivering liquid CO2 to the first liquid inlet pipe (11).

5. A CO2 transcritical freezing system according to claim 2, characterized in that: A channel (4) is provided on the outside of the liquid return branch pipe (121) and on the ground layer correspondingly, and the liquid return branch pipe (121) is accommodated and arranged inside the channel (4).

6. A CO2 transcritical freezing method, used in a CO2 transcritical freezing system as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: S1, determine the construction location: According to the hydrogeological conditions of the deep underground space and the wellbore to be constructed, the deep underground space and the area around the wellbore to be frozen are planned and determined; S2, hole making construction: A plurality of channels (4) are opened around the planned area to be frozen by deep drilling at equal intervals; S3, freeze equipment layout: A conduit (23) is connected between the storage tank (21) and the compressor (22), and then a second liquid inlet pipe (31) and a second liquid return pipe (32) having a pressurizing pump station (33) are respectively connected to the compressor (22), wherein the second liquid inlet pipe (31) is in communication with the first liquid inlet pipe (11), and the second liquid return pipe (32) is in communication with the first liquid return pipe (12); S4, freeze construction: A plurality of liquid return branch pipes (121) welded to the first liquid return pipe (12) are sequentially lowered into the plurality of channels (4) that have been opened, and then a liquid inlet branch pipe (111) welded to the first liquid inlet pipe (11) is inserted and installed inside each liquid return branch pipe (121). The pressure pump station (33) is turned on to transport low-temperature liquid CO2 into the channel (4) to freeze the poor strata around the area to be frozen to form a frozen wall, thereby ensuring that subsequent excavation construction in the area to be frozen proceeds normally.

7. A CO2 transcritical freezing method according to claim 6, characterized in that: The deep drilling method implemented in step S2 uses a drilling rig as the equipment.

8. A CO2 transcritical freezing method according to claim 7, characterized in that: In the deep drilling method in step S2, the equipment is calibrated every 5-10 m of drilling.

9. A CO2 transcritical freezing method according to claim 6, characterized in that: The plane shape planned on the area to be frozen in step S2 is consistent with the plane shape formed by the multiple channels (4) with deep holes around it.

10. A CO2 transcritical freezing method according to claim 6, characterized in that: The difference between the cross-sections of the liquid return branch pipe (121) and the liquid inlet branch pipe (111) used in step S4 is greater than the cross-sectional area of ​​the liquid inlet branch pipe (111).

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