Middle-deep geothermal energy buried pipe and heat exchange system

Abstract

The invention relates to a middle-deep layer geothermal energy buried pipe and a heat exchange system, and belongs to the field of middle-deep layer geothermal energy heat exchange. The medium-deep layer geothermal energy buried pipe and heat exchange system comprises a plurality of U-shaped pipe units, each U-shaped pipe unit comprises two plastic pipe bodies and an elbow used for connecting the two plastic pipe bodies, a hot melt adhesive layer is integrally connected to the inner wall of each plastic pipe body, and a spiral metal spiral piece is embedded in the inner wall of each hot melt adhesive layer. The existing medium-deep geothermal energy buried pipe and heat exchange system are optimized and improved, especially the internal structure of the buried pipe is optimized, so that the heat exchange efficiency of the buried pipe is further improved, and the buried pipe is particularly suitable for medium-deep geothermal energy; the larger the inner diameter of the buried pipe is, the better the heat exchange effect is, and therefore the utilization rate of medium-deep layer geothermal energy is further increased. The heat exchange efficiency of the heat exchange system is higher, the heat exchange system is particularly suitable for medium-deep layer geothermal heat exchange, and the deeper the geothermal well is, the larger the heat exchange effect difference is.

Description

Technical Field

[0001] The present invention relates to the technical field of mid-deep geothermal heat exchange, in particular to a mid-deep geothermal energy buried pipe and a heat exchange system. Background Art

[0002] Geothermal energy, the thermal energy stored within the Earth, is a clean, low-carbon, widely distributed, abundant, safe, and high-quality renewable energy source. Its development and utilization offers sustainable and stable energy supply, efficient recycling, and renewable potential. It can reduce greenhouse gas emissions and improve the ecological environment. It plays a crucial role in future clean energy development and is expected to become a new direction in the transformation of energy structures.

[0003] Medium- to deep-seated geothermal energy refers to thermal energy resources buried 200 to several thousand meters below the Earth's surface. Its temperature is typically above 25°C, with high heat reserves and stable heat supply. Compared to shallow geothermal energy, medium- to deep-seated geothermal energy requires more sophisticated extraction techniques, but it holds greater amounts of heat, making it suitable for a wider range of applications, such as industrial heating, greenhouse cultivation, geothermal power generation, and building heating.

[0004] During the construction of 2-3 geothermal wells in Liangxiang geothermal field, it was found that for medium and deep geothermal, if the heat exchange effect of buried pipes can be effectively improved, it will be beneficial to further improve the utilization rate of geothermal energy.

[0005] The development of medium- and deep-layer geothermal energy mainly relies on technologies such as geothermal wells and geothermal heat exchangers. Among them, geothermal wells are key facilities for obtaining geothermal energy. They are usually drilled deep underground to contact high-temperature rock formations or geothermal fluids.

[0006] Geothermal heat exchangers are a key component of geothermal energy utilization in deep and medium-depth geothermal regions. Common types include coaxial tube-in-tube and U-shaped heat exchangers. These extract heat energy from deep underground through a closed circulation system, then upgrade it through a geothermal pump unit for heating.

[0007] Currently, buried pipes are all plastic pipes (such as high-density polyethylene or polybutylene). For example, the inner diameter of a U-shaped pipe is generally less than 50 mm, primarily due to the need to minimize flow rates. Furthermore, the borehole diameter for buried pipes is typically 100 to 159 mm.

[0008] The length of buried pipes is usually more than 100 meters or even more than 200 meters. Most of the fluid in the pipe is in a laminar state, and generally only presents turbulent state at the inlet, turning point and outlet; coupled with the limitations of material reasons, these all restrict the improvement of the heat exchange efficiency of buried pipes.

[0009] Based on this, the present invention is proposed. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, the present invention provides a medium-deep geothermal energy buried pipe and heat exchange system, and its technical solution is as follows: A medium-deep geothermal energy buried pipe includes several U-shaped pipe units, each of which includes two plastic pipe bodies and an elbow for connecting the two plastic pipe bodies. The inner wall of the plastic pipe body is integrally connected with a hot melt adhesive layer, and the inner wall of the hot melt adhesive layer is embedded with a spiral metal spiral sheet.

[0011] As a further solution of the present invention, the material of the metal spiral sheet is copper alloy or aluminum alloy.

[0012] As a further solution of the present invention, the plastic tube is made of high-density polyethylene or polybutylene.

[0013] As a further solution of the present invention, the method for manufacturing the plastic tube body, the hot melt adhesive layer and the metal spiral sheet comprises the following steps: Step 1: Wrap a layer of metal spiral sheet around the surface of the metal core rod and tie the metal spiral sheet and the metal core rod tightly. Step 2: The cut hot melt adhesive sleeve is put on the outside of the metal core rod and the metal spiral sheet, and flame welding is used to seal along the cut seam of the hot melt adhesive sleeve; during the sealing process, a metal shaping sleeve is also used to correct and shape the hot melt adhesive sleeve being sealed, and the metal shaping sleeve moves in the same direction as the flame welding; Step 3: After the hot melt adhesive sleeve is sealed, a hot melt adhesive layer is formed, the metal shaping sleeve is removed, and a plastic tube body is formed on the surface of the hot melt adhesive layer using extrusion technology; Step 4: Pull out the metal core rod to obtain a composite pipe in which the plastic pipe body, the hot melt adhesive layer and the metal spiral sheet are connected as one.

[0014] As a further solution of the present invention, in step 1, before the metal core rod is used, a layer of release agent is coated on the surface of the metal core rod.

[0015] As a further solution of the present invention, in step 2, the cut seam of the hot melt adhesive sleeve is in the shape of a cylindrical spiral line.

[0016] As a further solution of the present invention, in step 2, before the metal shaping sleeve is used, a layer of release agent is coated on the inner wall of the metal core rod; during the process of correcting and shaping the hot melt adhesive sleeve being sealed, the metal shaping sleeve is cooled by blowing compressed air with a temperature below 15°C.

[0017] As a further solution of the present invention, in step 3, during the process of forming the plastic tube body by extrusion technology on the surface of the hot melt adhesive layer, the metal core rod is subjected to megasonic auxiliary vibration by an external megasonic transducer, and the megasonic frequency is 0.58 MHz.

[0018] As a further solution of the present invention, the hot melt adhesive layer is made of non-reactive hot melt adhesive doped with nickel sulfide, and the doping amount is 1.3%.

[0019] A heat exchange system comprises the aforementioned medium-deep geothermal energy buried pipe.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention optimizes and improves the existing medium-deep geothermal energy buried pipes and heat exchange systems, especially by optimizing the internal structure of the buried pipes, thereby further improving the heat exchange efficiency of the buried pipes, making them particularly suitable for medium-deep geothermal energy; the larger the inner diameter of the buried pipes, the better the heat exchange effect, thereby further improving the utilization rate of medium-deep geothermal energy.

[0021] The heat exchange system of the present invention has higher heat exchange efficiency and is particularly suitable for medium-deep geothermal heat exchange. The deeper the geothermal well, the greater the difference in heat exchange effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the variation curve of doping amount and minimum tensile strength; Figure 2 It is the curve of frequency and wax rod weight loss value. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to specific embodiments. The embodiments described below are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Example 1

[0024] A heat exchange system comprises a geothermal heat exchanger and a medium-deep geothermal energy buried pipe buried in a geothermal well.

[0025] A medium-deep geothermal energy buried pipe includes several U-shaped pipe units, each of which includes two plastic pipe bodies and an elbow for connecting the two plastic pipe bodies; the inner wall of the plastic pipe body is integrally connected with a hot melt adhesive layer, and the inner wall of the hot melt adhesive layer is embedded with a spiral metal spiral sheet.

[0026] The material of the metal spiral sheet is copper alloy with a thickness of 1.5 mm, the thickness of the hot melt adhesive layer is 1 mm, and the thickness of the plastic tube body is 2.5 mm; therefore, the wall thickness of the final composite tube is 3.5-4 mm; this is mainly because the depth of the metal spiral sheet embedded in the hot melt adhesive layer is 0.5-1 mm, so that there is a raised spiral structure with a thickness of 0-0.5 mm on the inner surface of the composite tube. The existence of this spiral structure, on the one hand, can break the laminar flow in the composite tube, thereby forming more turbulent flow in the composite tube, thereby maintaining a high heat exchange effect even in a high flow rate environment; coupled with the better thermal conductivity of the metal spiral sheet, the heat exchange effect can be further improved.

[0027] The material of the plastic tube body is high-density polyethylene.

[0028] The manufacturing method of the composite pipe composed of the plastic pipe body, the hot melt adhesive layer and the metal spiral sheet comprises the following steps: Step 1: First, apply a layer of polytetrafluoroethylene release agent on the surface of the metal core rod, then wrap a layer of metal spiral sheet on the surface, and tie the metal spiral sheet and the metal core rod tightly.

[0029] Step 2: Cut the hot-melt adhesive sleeve, where the cut seam is in the shape of a cylindrical spiral. The cut hot-melt adhesive sleeve is placed over the metal core rod and metal spiral sheet, and flame welding is used to seal the hot-melt adhesive sleeve along the cut seam. During the sealing process, a metal shaping sleeve is placed over the hot-melt adhesive sleeve to calibrate and shape the hot-melt adhesive sleeve, with the metal shaping sleeve advancing in the same direction as the flame welding. Prior to use, the metal shaping sleeve is coated with a layer of polytetrafluoroethylene release agent on the inner wall of the metal core rod. During the calibration and shaping process, the metal shaping sleeve is cooled by blowing compressed air at a temperature below 15°C. The hot-melt adhesive layer is a non-reactive hot-melt adhesive doped with 1.3% nickel sulfide. For example, a 1000g hot-melt adhesive layer contains 13g of doped nickel sulfide.

[0030] Step 3: After the hot melt adhesive sleeve is melt-sealed to form a hot melt adhesive layer, the metal shaping sleeve is removed, and a plastic tube body is formed on the surface of the hot melt adhesive layer using extrusion technology. During the process of forming the plastic tube body on the surface of the hot melt adhesive layer using extrusion technology, the metal core rod is subjected to megasonic assisted vibration through an external megasonic transducer, and the megasonic frequency is 0.58 MHz.

[0031] Step 4: Pull out the metal core rod to obtain a composite pipe in which the plastic pipe body, the hot melt adhesive layer and the metal spiral sheet are connected as one.

[0032] The above method is suitable for continuous processing, can ensure that the materials at each level are connected as one, can effectively avoid leakage risks, and improve production efficiency.

[0033] During the above manufacturing process, a portion of raised spiral metal spiral sheets will exist on the tube wall to prevent the tube wall from being too smooth and thus preventing turbulence from forming near the tube wall.

[0034] In addition, during the processing, when the seam is cut in the shape of the heat-welded cylindrical spiral, it is equivalent to the preliminary fixation of the hot-melt adhesive sleeve. Compared with the axial setting, such preliminary fixation has the best effect. During the subsequent hot-melt extrusion, the hot-melt adhesive sleeve will also be partially melted by the residual heat of the hot-melt extrusion. In order to ensure that a part of the metal spiral is embedded in the melted hot-melt adhesive, megasonic vibration assistance is required. Ultrasonic vibration (ultrasonic frequency is less than or equal to 200kHz) cannot be used in this area. Otherwise, almost most of the metal spirals may sink into the plastic pipe body, resulting in the inner wall of the final composite pipe being too smooth.

[0035] Because the hot melt adhesive used is a non-reactive type that reacts, heats, and solidifies, and because a polytetrafluoroethylene release agent is used during the production process, the bonding strength between the metal spiral and the composite tube would be limited without the addition of some nickel sulfide, aided by megasonic vibration. In Example 1, the minimum tensile strength was determined based on the minimum pulling force required to pull the metal spiral 2 cm. A greater minimum tensile strength indicates a better bond between the metal spiral and the composite tube. The minimum tensile strength in Example 1 was 1.51 kN. Example 2

[0036] A medium-deep geothermal energy buried pipe includes several U-shaped pipe units, each of which includes two plastic pipe bodies and an elbow for connecting the two plastic pipe bodies; the inner wall of the plastic pipe body is integrally connected with a hot melt adhesive layer, and the inner wall of the hot melt adhesive layer is embedded with a spiral metal spiral sheet.

[0037] The metal spiral sheet is made of aluminum alloy with a thickness of 1.5 mm, the hot melt adhesive layer is 1 mm thick, and the plastic tube body is 2.5 mm thick; therefore, the wall thickness of the final composite tube is 3.5-4 mm.

[0038] The material of the plastic tube is polybutylene. Example 3

[0039] A medium-deep geothermal energy buried pipe includes several U-shaped pipe units, each of which includes two plastic pipe bodies and an elbow for connecting the two plastic pipe bodies; the inner wall of the plastic pipe body is integrally connected with a hot melt adhesive layer, and the inner wall of the hot melt adhesive layer is embedded with a spiral metal spiral sheet.

[0040] The metal spiral sheet is made of copper alloy with a thickness of 1.5 mm, the hot melt adhesive layer is 1 mm thick, and the plastic pipe body is 2.5 mm thick; therefore, the wall thickness of the final composite pipe is 3.5-4 mm.

[0041] The material of the plastic tube is polybutylene. Comparative Example 1

[0042] In this example, the only difference from Example 1 is that annular ring pieces are embedded in the inner wall of the hot melt adhesive layer, and the ring pieces are arranged at equal intervals, with one set every 30 cm; all the ring pieces are equal in length to the metal spiral pieces in Example 1. Comparative Example 2

[0043] In this example, the only difference from Example 1 is that three long strips arranged along the axial direction are embedded in the inner wall of the hot melt adhesive layer, and the length of all the long strips is greater than the length of the metal spiral sheet in Example 1.

[0044] In a heat exchange simulation laboratory, the U-shaped tube unit was placed horizontally in a constant temperature water tank controlled at 100°C, the water inlet temperature was 20°C, and the flow rate within the tube was 0.2 L / s. The test measured the outlet water temperature 2 minutes after the water flowed out. The outlet water temperature of Example 1 was 33.2°C, the outlet water temperature of Comparative Example 1 was 31.5°C, and the outlet water temperature of Comparative Example 2 was 30.1°C. This shows that Example 1 has the best heat exchange performance. Comparative Example 3

[0045] In this example, as the doping amount changes, the minimum tensile strength curve is shown in Figure 1 ,Depend on Figure 1 It can be seen that the optimal doping amount is 1.3%. Comparative Example 4

[0046] Because the composite pipe has some raised metal spirals inside, its inner wall is not smooth. To measure this, take a 1-meter-long composite pipe and place a 30-cm-long, 10-cm-diameter polyethylene wax rod inside. Repeatedly raise and lower the composite pipe 100 times, measuring the weight loss of the polyethylene wax rod. This is the wax rod weight loss value. The greater the wax rod weight loss value, the less smooth the composite pipe's inner wall is.

[0047] In this example, as the frequency changes, the wax rod weight loss value change curve is shown in Figure 2 ,Depend on Figure 2 It can be seen that the optimal megasonic frequency is 0.58MHz. Figure 2 The 0MHz here means the megasonic transducer is not activated. The 0.2MHz refers to the ultrasonic transducer used.

[0048] In addition, it should be understood that those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment may also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A medium-deep geothermal energy buried pipe, comprising a plurality of U-shaped pipe units, each comprising two plastic pipe bodies and an elbow for connecting the two plastic pipe bodies, characterized in that: A hot melt adhesive layer is integrally connected to the inner wall of the plastic tube, and a spiral metal spiral sheet is embedded in the inner wall of the hot melt adhesive layer.

2. The medium-deep geothermal energy buried pipe according to claim 1, characterized in that: The material of the metal spiral piece is copper alloy or aluminum alloy.

3. The medium-deep geothermal energy buried pipe according to claim 1, characterized in that: The plastic tube is made of high-density polyethylene or polybutylene.

4. The medium-deep geothermal energy buried pipe according to claim 1, characterized in that: The method for manufacturing the plastic tube body, the hot melt adhesive layer and the metal spiral sheet comprises the following steps: Step 1: Wrap a layer of metal spiral sheet around the surface of the metal core rod and tie the metal spiral sheet and the metal core rod tightly. Step 2: The cut hot melt adhesive sleeve is put on the outside of the metal core rod and the metal spiral sheet, and flame welding is used to seal along the cut seam of the hot melt adhesive sleeve; during the sealing process, a metal shaping sleeve is also used to correct and shape the hot melt adhesive sleeve being sealed, and the metal shaping sleeve moves in the same direction as the flame welding; Step 3: After the hot melt adhesive sleeve is sealed, a hot melt adhesive layer is formed, the metal shaping sleeve is removed, and a plastic tube body is formed on the surface of the hot melt adhesive layer using extrusion technology; Step 4: Pull out the metal core rod to obtain a composite pipe in which the plastic pipe body, the hot melt adhesive layer and the metal spiral sheet are connected as one.

5. The medium-deep geothermal energy buried pipe according to claim 4, characterized in that: In step 1, before the metal core rod is used, a layer of release agent is coated on the surface of the metal core rod.

6. The medium-deep geothermal energy buried pipe according to claim 4, characterized in that: In step 2, the cut seam of the hot melt adhesive sleeve is in the shape of a cylindrical spiral line.

7. The medium-deep geothermal energy buried pipe according to claim 4, characterized in that: In step 2, before the metal shaping sleeve is used, a layer of release agent is applied to the inner wall of the metal core rod; during the process of correcting and shaping the hot melt adhesive sleeve being sealed, the metal shaping sleeve is cooled by blowing compressed air with a temperature below 15°C.

8. The medium-deep geothermal energy buried pipe according to claim 4, characterized in that: In step 3, during the process of forming the plastic tube body by extrusion technology on the surface of the hot melt adhesive layer, the metal core rod is subjected to megasonic auxiliary vibration by an external megasonic transducer, and the megasonic frequency is 0.58 MHz.

9. The medium-deep geothermal energy buried pipe according to claim 1, characterized in that: The hot melt adhesive layer is made of non-reactive hot melt adhesive doped with nickel sulfide, with a doping amount of 1.3%.

10. A heat exchange system, characterized in that: It comprises a medium-deep geothermal energy buried pipe as described in any one of claims 1 to 9.

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