Energy tunnel enhanced heat exchange system and method based on artificial freezing

Abstract

The invention discloses an energy tunnel enhanced heat exchange system and method based on artificial freezing, and relates to the field of energy tunnel enhanced heat exchange. An energy tunnel enhanced heat exchange method based on artificial freezing is characterized in that in the freezing stage, the critical carbon dioxide artificial stratum freezing technology is adopted for freezing an underground target freezing area; in the shield excavation stage, heat exchange energy pipe pieces are laid in an artificial freezing area, and heat exchange pipes are formed; in the system operation stage, the ground source heat pump is arranged on the energy tunnel loop, the energy tunnel loop obtains terrestrial heat through the heat exchange pipe, fluid in the heat exchange pipe is circulated through the ground source heat pump, and therefore continuous geothermal energy is provided for the using loop. An energy tunnel enhanced heat exchange system based on artificial freezing comprises an underground energy tunnel, a supercritical carbon dioxide refrigerator and a ground source heat pump, wherein the supercritical carbon dioxide refrigerator and the ground source heat pump are arranged on the ground. Cold energy of the stratum in the freezing period is effectively utilized, and the geothermal energy extraction efficiency of the energy tunnel is improved.

Description

Technical Field

[0001] The present invention relates to an enhanced heat exchange technology for an energy tunnel, and in particular to an enhanced heat exchange system and method for an energy tunnel based on artificial freezing. Background Art

[0002] For some coastal cities, subway tunnel construction requires passing through various complex strata such as soft soil or water-rich sand layers. Artificial freezing methods are needed to assist construction, thereby maintaining the stability of the surrounding soil and preventing groundwater intrusion, thereby ensuring the safety and reliability of subway operation. During the maintenance freezing period and thawing period, the ground cold will gradually lose with the increase of time; if the ground cold during the freezing period can be effectively utilized, it will be beneficial in many aspects such as energy conservation and emission reduction, cost reduction, multi-functional utilization, and increased energy supply, and has important economic and environmental benefits. Therefore, it is urgent to solve how to utilize the ground cold during the freezing process.

[0003] As a new type of ground source heat pump technology for shallow geothermal energy development, energy tunnel technology integrates tunnel structure with underground pipe heat exchange system, has the advantages of good heat transfer effect, high heat exchange efficiency, small footprint, low construction cost, etc., and has good application prospects in the field of engineering energy conservation. However, it is found in engineering applications that due to the single use of energy tunnel technology, the temperature difference between the stratum and the outside world is gradually decreasing. Therefore, it is foreseeable that when the temperature difference between the stratum and the outside world is small, there will be a bottleneck of low heat exchange efficiency, resulting in a decrease in the extraction efficiency of geothermal energy.

[0004] If the energy tunnel technology is used well in the artificial freezing area, not only can the coldness of the strata during the freezing period be effectively utilized, but also the geothermal energy extraction efficiency of the energy tunnel can be improved. Summary of the invention

[0005] In view of the above background, the present invention proposes an energy tunnel enhanced heat exchange system and method based on artificial freezing, which can effectively utilize the coldness of the strata during the freezing period, improve the geothermal energy extraction efficiency of the energy tunnel, and then effectively provide geothermal energy for other buildings, achieve energy conservation and emission reduction, reduce costs, multi-functional utilization and increase energy supply, and have important economic and environmental benefits.

[0006] One of the purposes of the present invention is to provide a method for enhancing heat exchange in an energy tunnel based on artificial freezing, which is a first-of-its-kind method in the field.

[0007] Furthermore, the second object of the present invention is to provide an energy tunnel enhanced heat exchange system based on artificial freezing, which effectively utilizes the coldness of the stratum during freezing, increases the heat exchange efficiency of the energy tunnel, and achieves energy conservation and emission reduction, cost reduction, multi-functional utilization and increased energy supply. The embodiment adopts prefabricated heat exchange energy segments to improve the safety of the segments during the heat exchange process, thereby further ensuring the geothermal energy extraction efficiency of the system energy tunnel, which is more conducive to promotion and application.

[0008] Technical solution of the present invention: The present invention proposes an energy tunnel enhanced heat exchange method based on artificial freezing. The method idea is as follows: in the freezing stage, the underground target freezing area is frozen by using critical carbon dioxide artificial ground freezing technology. In the shield excavation stage, heat exchange energy pipe segments are laid in the artificial freezing area, i.e., the underground target freezing area, to form heat exchange pipes. In the system operation stage, a ground source heat pump is arranged on the energy tunnel loop. The energy tunnel loop obtains geothermal energy through the heat exchange pipe. The use loop of the energy tunnel loop is connected to a building that uses energy. The fluid in the heat exchange pipe is circulated by the ground source heat pump, thereby providing a continuous supply of geothermal energy to the use loop.

[0009] The above method scheme: Because critical state carbon dioxide is used to achieve ground freezing, carbon dioxide in the environment is consumed and reduced, the environment is improved, and it is environmentally friendly. Effective extraction and utilization of ground coldness is achieved, while avoiding large fluctuations in ground temperature, which helps to maintain ground temperature balance and maintain the stability of the ground environment. Effective utilization of the coldness of the ground during the freezing period improves the geothermal energy extraction efficiency of the energy tunnel, and then effectively provides geothermal energy for other buildings, achieving energy conservation and emission reduction, reducing costs, multi-functional utilization and increasing energy supply, with important economic and environmental benefits.

[0010] Critical carbon dioxide formation freezing technology is safer than traditional water cooling or cryogenic liquid cooling technology. The use of critical carbon dioxide in underground formations can avoid the risk of formation liquefaction and groundwater level changes, and reduce contact with groundwater.

[0011] An energy tunnel enhanced heat exchange system based on artificial freezing includes an energy tunnel arranged underground, and a supercritical carbon dioxide refrigerator and a ground source heat pump arranged on the ground, wherein: The heat exchange tunnel contains a heat exchange pipe loop, which is formed by connecting the heat exchange pipes of each section of the heat exchange energy pipe segments after they are pieced together, and also includes a compression diameter freezing pipe; The heat exchange energy tube segment comprises a steel cage, a heat exchange tube, an input tube, an output tube and a concrete layer. The heat exchange tube is formed by sequentially assembling a plurality of heat exchange units into a C shape. The two ends of the heat exchange tube serve as the input end and the output end respectively. The heat exchange unit is U-shaped. The openings of two adjacent heat exchange units are staggered. The heat exchange tube is wound and pasted on the outer surface of the steel cage. The input pipe and the output pipe are both axially attached to the inner side of the steel cage, the output end of the input pipe is connected to the input end of the heat exchange pipe, and the input section of the output pipe is connected to the output end of the heat exchange pipe; The concrete layer is poured and formed outside the steel cage and wraps the steel cage, heat exchange pipes, input pipes and output pipes inside; Each of the intensified small-diameter freezing pipes is attached to the outer wall of the concrete layer in parallel with each other, and the input end of each of the intensified small-diameter freezing pipes is connected to the supercritical carbon dioxide circulation pipeline, the input end of the supercritical carbon dioxide circulation pipeline is connected to the cold air output end of the supercritical carbon dioxide refrigerator, the output end of the supercritical carbon dioxide circulation pipeline is connected to the input end of the supercritical carbon dioxide refrigerator, the ground source heat pump is connected to the building located on the ground through the heat pump pipeline, and the ground source heat pump is connected to the heat exchange pipe loop in the heat exchange tunnel through the refrigeration circulation pipeline.

[0012] Preferably, the number of heat exchange units is not less than nine.

[0013] As a preferred method, the concrete layer is divided into six identical arc segments, each arc segment is provided with an input interface and an output interface, the two ends of the input interface are respectively connected to the output end of the input pipe and the input end of the heat exchange pipe, and the two ends of the output interface are respectively connected to the input end of the output pipe and the output end of the heat exchange pipe.

[0014] As a preferred method, the heat exchange tubes in the heat exchange energy tube segment are arranged in a longitudinal bow shape. On the one hand, it can increase the heat exchange area, and on the other hand, it can avoid excessive temperature stress at the joints of the tube segments due to large temperature differences, which can effectively increase the safety of the energy heat exchange tube segment during use.

[0015] As a preferred method, the inner diameter of the heat exchange tube is not less than 10 mm, and the inner diameter of the input tube and the output tube is not less than 50 mm.

[0016] As a preferred method, L-shaped butt joints are used between heat exchange energy segments.

[0017] The above system technical solution has a simple and safe structure and is easy to construct and apply. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the method of the present invention; Figure 2 It is a schematic diagram of the system and energy tunnel scenario of the present invention; Figure 3 It is a schematic diagram of the energy tunnel and underground target freezing area; Figure 4 It is a cross-sectional schematic diagram of a heat exchange energy tube segment; Figure 5 This is a schematic diagram of heat exchange energy tube segment assembly; Figure 6 Schematic diagram of the heat exchange tubes inside the heat exchange energy tube segment. DETAILED DESCRIPTION

[0019] A method for enhancing heat transfer in energy tunnels based on artificial freezing, such as Figure 1 As shown: During the freezing stage, critical carbon dioxide artificial ground freezing technology is used to freeze the underground target freezing area.

[0020] During the shield excavation stage, heat exchange energy segments are laid in the artificial freezing area, i.e. the underground target freezing area, to form heat exchange tubes.

[0021] During the system operation stage, a geothermal heat pump is installed on the energy tunnel loop. The energy tunnel loop obtains geothermal heat through heat exchange pipes. The use loop of the energy tunnel loop is connected to buildings that use energy. The fluid in the heat exchange pipes is circulated through the geothermal heat pump, thereby providing a steady supply of geothermal energy for the use loop.

[0022] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0023] Example 1 An energy tunnel enhanced heat exchange construction method based on artificial freezing, comprising: Step 1: Prefabrication stage construction The heat exchange tube 52 is arranged on the steel cage of the assembled heat exchange energy tube segment 5, and the tube segment joint space and the heat exchange unit 521 are reserved at the transverse center position of the heat exchange energy tube segment. The diameter of the heat exchange tube is not less than 10 mm, and the heat exchange tube is arranged in a transverse bow shape, with the number of arranged layers being not less than 9.

[0024] Step 2: Construction in the underground target freezing area 1 According to the design requirements, holes are drilled in the underground target freezing area and injection pipes (not shown) are installed. The injection pipes are used to inject critical carbon dioxide into the underground target freezing area and circulate the coolant. During the construction process, temperature and pressure sensors are installed to monitor and record the temperature and pressure in the underground target freezing area in real time to ensure the control and adjustment of the freezing effect. After a certain period of injection and circulation, the freezing effect is evaluated.

[0025] Step 3: Shield machine excavation When the expected freezing effect is achieved, a shield machine is used for excavation and prefabricated heat exchange energy segments are assembled, with every 6 heat exchange energy segments assembled into a ring.

[0026] Step 4: Set up the inlet and outlet pipes of the heat exchange energy segment. The pipe diameter should not be less than 50mm. At the same time, connect each ring of heat exchange pipes to the inlet and outlet loops.

[0027] Step 5, iterate step 2 to step 4, in this way, use the shield machine tunnel to continuously excavate the target construction area, and assemble prefabricated energy segments to continuously increase the length of the energy tunnel until the length of the energy tunnel reaches the construction target.

[0028] Step 6: Testing and Evaluation Phase After the construction is completed, the sealing and heat exchange performance of the entire heat exchange pipe loop composed of many heat exchange energy segments are tested.

[0029] Step 7: Construct energy tunnel system loop and application Connect the heat exchange pipe loop to the energy tunnel loop, set up an energy pump on the energy tunnel loop, and connect the building's energy use loop to the energy tunnel loop. After the energy tunnel is put into use, geothermal energy can be obtained through the heat exchange pipe, and the energy tunnel system provides a steady stream of geothermal energy for the use loop.

[0030] Example 2 Based on the method innovation of the present invention, Example 2 provides the system structure of the present invention.

[0031] like Figure 2 to Figure 6 As shown: An energy tunnel enhanced heat exchange system based on artificial freezing includes a heat exchange tunnel 2 arranged underground, and a supercritical carbon dioxide refrigerator 3 and a ground source heat pump 4 arranged on the ground, wherein: The heat exchange tunnel 2 contains a heat exchange pipe loop, which is formed by connecting the heat exchange pipes 52 of the heat exchange energy segments 5 after they are pieced together piece by piece. The heat exchange energy segments include a steel cage 51, a heat exchange pipe 52, an input pipe 53, an output pipe 54 and a concrete layer 55. The heat exchange pipe 52 is formed by sequentially pieced together a plurality of heat exchange units 521 to form a C shape. The two ends of the heat exchange pipe 52 serve as the input end and the output end respectively. The heat exchange unit 521 is U-shaped. The openings of two adjacent heat exchange units 521 are staggered. The heat exchange pipe 52 is wound and attached to the outer surface of the steel cage 51. The input pipe 53 and the output pipe 54 are both axially attached to the inner side of the steel cage 51, the output end of the input pipe 53 is connected to the input end of the heat exchange pipe 52, and the input section of the output pipe 54 is connected to the output end of the heat exchange pipe 52; The concrete layer 55 is cast outside the steel cage 51 and wraps the steel cage 51, the heat exchange tube 52, the input tube 53 and the output tube 54; Each of the intensified small-diameter freezing pipes 31 is attached to the outer wall of the concrete layer 55 in parallel with each other, and the input end of each of the intensified small-diameter freezing pipes 31 is connected to the supercritical carbon dioxide circulation pipe 32, the input end of the supercritical carbon dioxide circulation pipe 32 is connected to the cold air output end of the supercritical carbon dioxide refrigerator 3, and the output end of the supercritical carbon dioxide circulation pipe 32 is connected to the input end of the supercritical carbon dioxide refrigerator 3. The ground source heat pump 4 is connected to the building 6 located on the ground through the heat pump pipeline 41, and the ground source heat pump 4 is connected to the heat exchange pipe loop in the heat exchange tunnel 2 through the refrigeration circulation pipeline 42.

[0032] In this embodiment: The number of heat exchange units 521 is not less than nine; The concrete layer 55 is composed of six identical arc segments 551, each of which is provided with an input interface 531 and an output interface 541. The two ends of the input interface 531 are respectively connected to the output end of the input pipe 53 and the input end of the heat exchange pipe 52, while the two ends of the output interface 541 are respectively connected to the input end of the output pipe 54 and the output end of the heat exchange pipe 52.

[0033] In this embodiment: The working medium of the ground source heat pump 4 is water.

[0034] In this embodiment: The heat exchange energy segments can exchange heat with the surrounding soil. The heat exchange tubes in the heat exchange energy segments are arranged in a longitudinal bow shape, which can increase the heat exchange area on the one hand and avoid excessive temperature stress at the segment joints due to large temperature differences on the other hand.

[0035] The inner diameter of the heat exchange tube 52 is not less than 10 mm, and the inner diameters of the input tube 53 and the output tube 54 are not less than 50 mm.

[0036] The L-shaped butt joint between the heat exchange energy segments fundamentally reduces the problem of temperature stress concentration caused by the heat exchange process. This design significantly reduces the deformation of the heat exchange energy segment joints and improves the stability of the overall structure.

[0037] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for enhancing heat exchange in an energy tunnel based on artificial freezing, characterized by: In the freezing stage, critical carbon dioxide artificial ground freezing technology is used to freeze the underground target freezing area; During the shield excavation stage, heat exchange energy segments are laid in the artificial freezing area, i.e., the underground target freezing area, to form heat exchange pipes; During the system operation stage, a geothermal heat pump is installed on the energy tunnel loop. The energy tunnel loop obtains geothermal heat through heat exchange pipes. The use loop of the energy tunnel loop is connected to buildings that use energy. The fluid in the heat exchange pipes is circulated by the geothermal heat pump, thereby providing geothermal energy to the use loop.

2. The method for enhancing heat exchange in an energy tunnel based on artificial freezing as claimed in claim 1, characterized in that: include: Step 1: Prefabrication stage construction Arrange heat exchange tubes on the steel cage of the assembled heat exchange energy tube segment; Step 2: Construction in the underground target freezing area According to the design requirements, drilling is performed in the underground target freezing area, and an injection pipeline is installed, wherein the injection pipeline is used to inject critical carbon dioxide into the underground target freezing area and circulate and transport the coolant; Step 3: Shield machine excavation When the expected freezing effect is achieved, a shield machine is used for excavation and prefabricated heat exchange energy segments are assembled. Every 6 heat exchange energy segments are assembled into a ring. Step 4: Set the inlet and outlet pipes of the heat exchange energy tube segment, and connect each ring of heat exchange pipes to the inlet and outlet circuits; Step 5, iterating step 2 to step 4, in this way, using the shield machine tunnel to continuously excavate the target construction area, and assembling prefabricated energy segments to continuously increase the length of the energy tunnel until the length of the energy tunnel reaches the construction target; Step 6: Testing Phase After the construction is completed, the sealing and heat exchange performance of the entire heat exchange pipe loop composed of many heat exchange energy segments are tested; Step 7: Construct energy tunnel system loop and application Connect the heat exchange pipe loop to the energy tunnel loop, set an energy pump on the energy tunnel loop, and connect the building's energy usage loop to the energy tunnel loop; after the energy tunnel is put into use, geothermal energy is obtained through the heat exchange pipe, and the energy tunnel system provides geothermal energy for the usage loop.

3. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 2 is characterized by: It includes an underground heat exchange tunnel, as well as a supercritical carbon dioxide refrigerator and ground-source heat pump on the ground.

4. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 3 is characterized by: The heat exchange tunnel contains a heat exchange pipe loop, which is formed by connecting the heat exchange pipes of each section of the heat exchange energy pipe segments after they are pieced together, and also includes a compression diameter freezing pipe; The heat exchange energy pipe segment includes a steel cage, a heat exchange tube, an input tube, an output tube and a concrete layer. The heat exchange tube is formed by a plurality of heat exchange units assembled in sequence to form a C shape. The two ends of the heat exchange tube are respectively used as the input end and the output end. The heat exchange unit is U-shaped. The openings of two adjacent heat exchange units are staggered. The heat exchange tube is wound and pasted on the outer surface of the steel cage. The input tube and the output tube are both axially pasted on the inner side of the steel cage. The output end of the input tube is connected to the input end of the heat exchange tube, and the input section of the output tube is connected to the output end of the heat exchange tube. The concrete layer is cast and formed outside the steel cage and wraps the steel cage, the heat exchange tube, the input tube and the output tube inside. Each of the intensified small-diameter freezing pipes is attached to the outer wall of the concrete layer in parallel with each other, and the input end of each of the intensified small-diameter freezing pipes is connected to the supercritical carbon dioxide circulation pipeline, the input end of the supercritical carbon dioxide circulation pipeline is connected to the cold air output end of the supercritical carbon dioxide refrigerator, the output end of the supercritical carbon dioxide circulation pipeline is connected to the input end of the supercritical carbon dioxide refrigerator, the ground source heat pump is connected to the building located on the ground through the heat pump pipeline, and the ground source heat pump is connected to the heat exchange pipe loop in the heat exchange tunnel through the refrigeration circulation pipeline.

5. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 4 is characterized by: The number of the heat exchange units is no less than nine.

6. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 4 is characterized by: The concrete layer is composed of six identical arc segments, each arc segment is provided with an input interface and an output interface, the two ends of the input interface are respectively connected to the output end of the input pipe and the input end of the heat exchange pipe, and the two ends of the output interface are respectively connected to the input end of the output pipe and the output end of the heat exchange pipe.

7. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 4 is characterized by: The heat exchange tubes in the heat exchange energy tube sheet are arranged in a longitudinal bow shape.

8. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 4 is characterized by: The inner diameter of the heat exchange tube is not less than 10 mm, and the inner diameters of the input tube and the output tube are not less than 50 mm.

9. The energy tunnel enhanced heat exchange system constructed by the energy tunnel enhanced heat exchange method based on artificial freezing as claimed in claim 4 is characterized by: The heat exchange energy tube segments are butt-jointed in an L-shaped manner.

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