Co 2transcritical freezing system and freezing method

Abstract

The present invention relates to the technical field of deep underground space stratum reinforcement, and particularly to a CO2 transcritical freezing system and freezing method. The system comprises: a freezing subsystem comprising a first liquid intake pipe and a first liquid return pipe which are arranged on the ground and are configured to convey low-temperature liquid CO2 to the stratum for stratum freezing construction; a liquefaction subsystem for compressing the volume of normal-temperature gaseous CO2, such that the movement of molecules between the gaseous CO2 is restricted and reduced, and the gaseous CO₂ is converted into low-temperature liquid CO2; and an intake and return pipeline subsystem. CO2 media used in the present invention effectively solves the problems of flammability and explosibility, high risk and difficulty in treatment, environmental pollution, etc., caused by liquid ammonia and brine used in traditional freezing construction. Further, a water-bearing stratum, a weak stratum, etc., are frozen and reinforced by means of compression-converted low-temperature liquid CO2 to form a water-proof stratum and a temporary support, thereby effectively preventing seepage of water and sinking, displacement and collapse of a wall surface and a bottom plate, and improving the stability of a frozen area to be excavated.

Description

A transcritical CO2 freezing system and freezing method Technical Field

[0001] This invention relates to the field of deep underground space stratum reinforcement technology, and particularly to the field of freezing construction in deep underground spaces and well shafts passing through aquifers, soft soil, soft rock, fracture zones and other unfavorable strata. Specifically, it relates to a CO2 transcritical freezing system and freezing method. Background Technology

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

[0003] Currently, 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, which uses liquid ammonia and brine as the medium and coolant. However, the liquid ammonia used is flammable and explosive, posing a high safety risk. Large amounts of brine are difficult to handle and pollute the environment. As a result, the freezing method has certain defects in actual construction and cannot meet the requirements of safety, efficiency and environmental protection.

[0004] The above content is only used to help understand the technical solution of the present invention, and does not represent an admission that the above content is the closest prior art. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a CO2 transcritical freezing system and freezing method.

[0006] To solve the above-mentioned 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 located above the formation, which are used to deliver low-temperature liquid CO2 to the formation for freezing construction.

[0008] The liquefaction subsystem is used to compress the volume of room-temperature gaseous CO2, thereby restricting and reducing the movement of molecules between gaseous CO2 molecules, and transforming it into low-temperature liquid CO2.

[0009] The inlet and outlet pipeline subsystem is used to circulate the cryogenic liquid CO2 that flows through the freezing subsystem.

[0010] Furthermore, the freezing subsystem also includes:

[0011] Multiple inlet branch pipes are evenly distributed below the first inlet pipe and are used for insertion into the formation.

[0012] The return branch pipes are located below the first return branch pipe and are evenly distributed in multiples, and are spaced out on the outside of the inlet branch pipe.

[0013] Furthermore, the liquefaction subsystem includes:

[0014] Storage tank, a sealed container used for storing gaseous CO2;

[0015] A compressor is used to compress the gaseous CO2 inside the storage tank and convert it into cryogenic liquid CO2.

[0016] A conduit is provided between the storage tank and the compressor to uniformly distribute and transport the gaseous CO2 filling the storage tank to the compressor.

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

[0018] The second liquid inlet pipe is located 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] The second return pipe is connected to the first return pipe and is installed on the compressor, and is used to return the liquid CO2 that has entered the formation into the compressor.

[0020] A pressurized pump station is installed on the delivery pipeline of the second inlet pipe to provide power for the delivery of liquid CO2 to the first inlet pipe.

[0021] Furthermore, a channel extending from top to bottom is provided on the outside of the return branch pipe and correspondingly on the stratum, and the return branch pipe is housed inside the channel.

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

[0023] S1, Determine the construction location:

[0024] Based on the hydrogeological conditions of the underground deep space and well shaft to be constructed, the area to be frozen around the underground deep space and well shaft is planned and determined.

[0025] S2, Hole drilling construction:

[0026] Multiple equally spaced channels were opened around the planned area to be frozen using deep drilling.

[0027] S3, Layout of freezing equipment:

[0028] Connect the conduit between the storage tank and the compressor, and then connect the second inlet pipe and the second return pipe with a pressurization pump station to the compressor respectively. The second inlet pipe is connected to the first inlet pipe, and the second return pipe is connected to the first return pipe.

[0029] S4, Freeze Construction:

[0030] Multiple return liquid branch pipes, welded to the first return liquid pipe, are sequentially lowered into the multiple channels. Then, an inlet branch pipe, welded to the first inlet pipe, is installed inside each return liquid branch pipe. The pressurization pump station is turned on to transport low-temperature liquid CO2 into the channel to freeze the unfavorable strata around the area to be frozen, forming a frozen wall to ensure the normal progress of subsequent excavation work in the area to be frozen.

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

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

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

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

[0035] Compared with existing technologies, the present invention has the following beneficial effects: The CO2 medium used in the present invention effectively solves the problems of flammability, explosiveness, high risk, difficulty in handling, and environmental pollution caused by liquid ammonia and brine used in traditional freezing construction, thus meeting the requirements of safety, efficiency and environmental protection; it also freezes and reinforces aquifers and soft strata by compressing and converting low-temperature liquid CO2, forming a waterproof layer and temporary support, effectively preventing water seepage and settlement, displacement and collapse of the wall and bottom plate, 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. Attached Figure Description

[0036] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

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

[0038] Figure 2 is a schematic diagram of a planar arrangement structure according to an embodiment of the present invention;

[0039] Figure 3 is a schematic diagram of the elevation layout structure according to an embodiment of the present invention;

[0040] Figure 4 is an enlarged view of the structure at point A in Figure 3.

[0041] In the diagram: 1. Freezing subsystem; 11. First inlet pipe; 111. Inlet branch pipe; 12. First return pipe; 121. Return branch pipe; 2. Liquefaction subsystem; 21. Storage tank; 22. Compressor; 23. Conduit; 3. Inlet and return pipeline subsystem; 31. Second inlet pipe; 32. Second return pipe; 33. Pressurization pump station; 4. Channel. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within 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 positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0044] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, "multiple" refers to two or more. Moreover, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0045] As shown in Figures 1-4, 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 installed above the formation, which are used to transport low-temperature liquid CO2 to the formation for freezing construction.

[0047] Liquefaction subsystem 2 is used to compress the volume of room temperature gaseous CO2, thereby restricting and reducing the movement of molecules between gaseous CO2 molecules, and transforming it into low temperature liquid CO2.

[0048] The inlet and outlet pipeline subsystem 3 is used to circulate the cryogenic liquid CO2 that flows through the freezing subsystem 1.

[0049] In practice, the liquefaction subsystem 2 converts gaseous CO2 at room temperature into high-pressure, low-temperature liquid CO2 at -30°C to -50°C. Through the conversion of CO2 at different pressures and states, the low-temperature liquid CO2 is transported to the target formation through the first inlet pipe 11 and the first return pipe 12 included in the freezing subsystem 1 for freezing, forming a water-proof layer and improving the properties of the frozen formation. The liquid CO2 that enters the formation is returned to the liquefaction subsystem 2 through the inlet and return pipeline subsystem 3, forming a circulating transport path, ensuring the utilization rate of liquid CO2, and minimizing the uneven temperature of the transported liquid CO2.

[0050] The first inlet pipe 11 and the first return pipe 12 included in the freezing subsystem 1 both adopt a ring structure, and the planar shape of the first inlet pipe 11 and the first return pipe 12 conforms to the shape of the top opening of the area to be frozen.

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

[0052] Multiple liquid inlet branch pipes 111 are located below the first liquid inlet pipe 11 and are evenly distributed therein, for insertion into the formation.

[0053] Multiple return branch pipes 121 are located below the first return pipe 12 and are evenly distributed, and are spaced out from the outside of the inlet branch pipes 111. This design, by evenly welding multiple inlet branch pipes 111 to the lower surface of the first inlet pipe 11 and multiple return branch pipes 121 to the lower surface of the first return pipe 12, and by combining the corresponding inlet branch pipes 111 and return branch pipes 121, allows the cryogenic liquid CO2 transported to the formation through the inlet branch pipes 111 to freeze the formation, and then transported back to the inlet / outlet pipeline subsystem 3 through the return branch pipes 121, effectively avoiding uneven temperature distribution of the transported liquid CO2.

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

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

[0056] Storage tank 21 is a sealed container used for storing gaseous CO2.

[0057] Compressor 22 is used to compress the gaseous CO2 inside the storage tank 21 and convert it into cryogenic liquid CO2.

[0058] The conduit 23, located between the storage tank 21 and the compressor 22, is used to evenly distribute and transport the gaseous CO2 filled inside the storage tank 21 to the compressor 22. This design, with the conduit 23 connected to the storage tank 21 and the compressor 22 at both ends respectively, allows the storage tank 21, which consists of two or more rigid, sealed containers storing gaseous CO2, to have a ball valve at its upper part for connecting to a gaseous CO2 filling device, ensuring a sufficient supply of gaseous CO2. At its lower part, the conduit 23, equipped with a ball valve structure, connects to three or more compressors 22. This allows the compressors 22 to perform work, converting the gaseous CO2 at room temperature into high-pressure, low-temperature liquid CO2 at -30°C to -50°C.

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

[0060] In one embodiment, the inlet and outlet piping subsystem 3 includes:

[0061] The second liquid inlet pipe 31 is disposed 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] The second return pipe 32 is connected to the first return pipe 12 and is installed on the compressor 22, for returning liquid CO2 that has entered the formation into the compressor 22.

[0063] A booster pump station 33, installed on the delivery pipeline of the second inlet pipe 31, provides power for the delivery of liquid CO2 to the first inlet pipe 11. This design, with the second inlet pipe 31 welded to the first inlet pipe 11 and one end connected to the outlet of the compressor 22 via a ball valve, allows the booster pump station 33 connected to the second inlet pipe 31 to deliver high-pressure, low-temperature liquid CO2 towards the first inlet pipe 11, until it enters the formation through multiple inlet branch pipes 111 welded to the lower surface of the first inlet pipe 11. Conversely, with the second return pipe 32 welded to the first return pipe 12 and one end connected to the return end of the compressor 22 via a ball valve, the liquid CO2 entering the formation can be circulated back into the compressor 22, achieving a closed-loop circulation delivery effect and preventing uneven temperature distribution of the low-temperature liquid CO2 during delivery within the formation.

[0064] In one embodiment, a channel 4 is provided on the outside of the return branch pipe 121 and correspondingly in the stratum, extending from top to bottom, and the return branch pipe 121 is housed inside the channel 4. This design allows for deep drilling operations using a rotary drilling rig around the area to be frozen, with the drilling depth and diameter fully accommodating the return branch pipe 121. The metal wall of the return branch pipe 121 facilitates heat exchange, freezing the soil layer near the channel 4 to form a frozen wall, achieving the same effect as pile foundation support and ensuring safe construction operations in the area to be frozen.

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

[0066] S1, Determine the construction location:

[0067] Based on the hydrogeological conditions of the underground deep space and well shaft to be constructed, the area to be frozen around the underground deep space and well shaft is planned and determined.

[0068] S2, Hole drilling construction:

[0069] Multiple equally spaced channels were opened around the planned area to be frozen using deep drilling.

[0070] S3, Layout of freezing equipment:

[0071] A conduit 23 is connected between the storage tank 21 and the compressor 22. Then, a second inlet pipe 31 and a second return pipe 32 with a pressurization pump station 33 are connected to the compressor 22 respectively. The second inlet pipe 31 is connected to the first inlet pipe 11, and the second return pipe 32 is connected to the first return pipe 12.

[0072] S4, Freeze Construction:

[0073] Multiple return liquid branch pipes 121, which are welded to the first return liquid pipe 12, are sequentially lowered into the multiple channels 4. Then, an inlet branch pipe 111, which is welded to the first inlet pipe 11, is inserted into each return liquid branch pipe 121. The pressurization pump station 33 is turned on to transport low-temperature liquid CO2 into the channel 4 to freeze the unfavorable strata around the area to be frozen, forming a frozen wall to ensure that the subsequent excavation work in the area to be frozen can proceed normally.

[0074] In practice, the CO2 compressor 22 performs work to convert gaseous CO2 at room temperature into high-pressure, low-temperature liquid CO2 at -30°C to -50°C. Through the conversion of CO2 at different pressures and states, the low-temperature liquid CO2 is transported to the required freezing stratum, thereby improving the freezing properties of the stratum and meeting the needs of construction.

[0075] In one embodiment, the deep drilling method implemented in step S2 uses a drilling rig. This design is suitable for penetrating different types of soil, cutting the soil by rotating the drill bit to perform deep drilling operations in the strata, and has good operability.

[0076] In one embodiment, the equipment is calibrated every 5-10 meters during the deep drilling process in step S2. This design strictly controls internal deviation, promptly corrects excessive deviation, and generates a drilling deviation diagram in a timely manner. Holes that do not meet design requirements must be patched to ensure the accuracy of hole position and depth.

[0077] In one embodiment, the planar shape planned on the area to be frozen in step S2 corresponds to the planar shape formed by the multiple deep-drilled channels 4 around it. This design allows for freezing of the surrounding area in accordance with the planar shape planned on the area to be frozen, avoiding water seepage and displacement, subsidence, and collapse of the supporting wall during subsequent construction operations, thereby improving the stability and quality of the area to be frozen.

[0078] In one embodiment, the difference in cross-section between the return branch pipe 121 and the inlet branch pipe 111 used in step S4 is greater than the cross-sectional area of ​​the inlet branch pipe 111. This design allows the inlet branch pipe 111 to be fitted inside the return branch pipe 121 with sufficient space to ensure that the incoming liquid CO2 quickly freezes the soil layer near channel 4, while also ensuring the normal operation of the return circulation. This avoids uneven temperature distribution of the liquid CO2, improves the freezing efficiency of the liquid CO2, and results in good performance.

[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 invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A CO2 transcritical freezing system, characterized in that, include: The freezing subsystem (1) includes a first liquid inlet pipe (11) and a first liquid return pipe (12) installed above the formation, which are used to transport low-temperature liquid CO2 to the formation for formation freezing construction. The liquefaction subsystem (2) is used to compress the volume of room temperature gaseous CO2, thereby restricting and reducing the movement of molecules between gaseous CO2 molecules, and transforming it into low temperature liquid CO2. The inlet and outlet pipeline subsystem (3) is used to return the cryogenic liquid CO2 that flows through the freezing subsystem (1) for circulation.

2. The CO2 transcritical freezing system according to claim 1, characterized in that, The freezing subsystem (1) also includes: A liquid inlet branch pipe (111) is located below the first liquid inlet pipe (11) and is provided in multiple evenly, for insertion into the formation; The return branch pipe (121) is located at the lower part of the first return pipe (12) and is evenly provided in multiples, and is spaced out outside the inlet branch pipe (111).

3. The CO2 transcritical freezing system according to claim 1, characterized in that, The liquefaction subsystem (2) includes: Storage tank (21), a sealed container for storing gaseous CO2; Compressor (22) is used to compress the gaseous CO2 inside the storage tank (21) and convert it into cryogenic liquid CO2; A conduit (23) is disposed between the storage tank (21) and the compressor (22) for uniformly distributing and transporting the gaseous CO2 filled inside the storage tank (21) to the compressor (22).

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

5. A CO2 transcritical freezing system according to claim 2, characterized in that: The return branch pipe (121) is provided with a channel (4) that runs from top to bottom on the outside of the stratum, and the return branch pipe (121) is housed inside the channel (4).

6. A transcritical CO2 freezing method, used in any one of the transcritical CO2 freezing systems as described in claims 1-5, characterized in that, Includes the following steps: S1, Determine the construction location: Based on the hydrogeological conditions of the underground deep space and well shaft to be constructed, the area to be frozen around the underground deep space and well shaft is planned and determined. S2, Hole drilling construction: Multiple equally spaced channels were opened around the planned area to be frozen using deep drilling (4); S3, Freezing equipment layout: A conduit (23) is connected between the storage tank (21) and the compressor (22). Then, a second inlet pipe (31) and a second return pipe (32) with a pressurization pump station (33) are connected to the compressor (22). The second inlet pipe (31) is connected to the first inlet pipe (11), and the second return pipe (32) is connected to the first return pipe (12). S4, Freeze Construction: Multiple return pipes (121) welded to the first return pipe (12) are sequentially lowered into the multiple channels (4) opened. Then, an inlet pipe (111) welded to the first inlet pipe (11) is inserted into each return pipe (121). The pressurization pump station (33) is turned on to transport low-temperature liquid CO2 into the channel (4) to freeze the unfavorable strata around the area to be frozen, forming a frozen wall to ensure that the subsequent excavation of the area to be frozen can proceed normally.

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

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

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

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

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