A jacketed heat exchanger for promoting geothermal heat recovery by natural circulation

Abstract

A casing heat exchanger for promoting geothermal heat recovery through natural circulation relates to a casing heat exchanger. The outer casing extends into a heat source well, and the inner heat preservation tube is coaxially arranged inside the outer casing. The bottom end of the inner heat preservation tube is connected to a water suction pipe, and the top end of the inner heat preservation tube extends out of the top end of the outer casing. A plurality of openings of the heat circulation hole are vertically spaced apart and arranged on the wall of the inner heat preservation tube. The upper edge of the uppermost opening of the heat circulation hole is 2 / 3 of the depth of the heat source well from the wellhead. The outlet pipe section is connected to the top end of the inner heat preservation tube, and the inlet pipe section is connected to the outer casing. The outlet pipe section and the inlet pipe section are connected to the evaporator side of the ground source heat pump unit. The heat circulation pipe connects the middle positions of the outlet pipe section and the inlet pipe section. Through the arrangement of the heat circulation hole and the heat circulation pipe, the fluid forms two natural circulations up and down under the action of thermal buoyancy during the non-heating period, accelerates the heat recovery of the surrounding rock and soil, is simple and stable, and has high economic efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to a double-pipe heat exchanger, in particular to a double-pipe heat exchanger for promoting geothermal heat recovery through natural circulation, and belongs to the technical field of geothermal energy application. BACKGROUND

[0002] The medium-deep geothermal heat pump is a high-efficiency, stable and zero-carbon heating technology, and the depth of the heat source well can reach 1500-3500m, and the bottom temperature is as high as 80℃, which is a promising green heat energy alternative solution.

[0003] The medium-deep geothermal heat pump system extracts underground heat energy through a buried pipe heat exchanger, and the buried pipe often adopts a coaxial double-pipe form, which is a closed cycle and can effectively protect groundwater resources. It is composed of an outer sleeve and an inner heat preservation pipe. During the heating period, the cold fluid from the ground source heat pump evaporator side enters the annular cavity between the outer pipe and the inner pipe, exchanges heat with the surrounding rock-soil during downward flow, the temperature rises, and the hot fluid flows out from the inner pipe and enters the ground source heat pump evaporator side, forming a closed heat extraction cycle.

[0004] However, as the operation time increases, the heat stored in the underground rock-soil will decrease year by year, resulting in a decrease in the average temperature or heat exchange capacity of the evaporator side, reducing the energy efficiency of the system. Many projects and practices do not set up heat recovery measures, resulting in an increase in energy consumption or insufficient heating capacity during long-term operation. At present, the heat recovery method mainly supplements heat to the underground through solar energy, cooling towers, etc., but this method will significantly increase the initial investment, and the economic efficiency is not optimistic. Therefore, it is urgent to improve and explore the geothermal heat recovery method, and find a more economical geothermal heat recovery method. SUMMARY

[0005] To solve the problems in the background art, the present application provides a double-pipe heat exchanger for promoting geothermal heat recovery through natural circulation, which forms two natural circulations up and down under the action of thermal buoyancy by setting a thermal circulation hole and a thermal circulation pipe during the non-heating period, accelerates the heat recovery of the surrounding rock-soil, is simple and stable, and has high economic efficiency.

[0006] In order to achieve the above object, the present application adopts the following technical scheme: a casing heat exchanger for promoting geothermal heat recovery through natural circulation, comprising an outer casing, an inner heat preservation tube, a heat circulation hole, a water suction tube, an outlet pipe section, a heat circulation pipe and an inlet pipe section, the top end and the bottom end of the outer casing are closed and extend into a heat source well, the inner heat preservation tube is coaxially arranged inside the outer casing, the bottom end of the inner heat preservation tube is connected to the water suction tube and is spaced from the bottom end of the outer casing, the top end of the inner heat preservation tube extends out of the top end of the outer casing and is connected and fixed thereto, a plurality of openings of the heat circulation hole are vertically spaced apart and arranged on the wall of the inner heat preservation tube, the upper edge of the uppermost opening of the heat circulation hole is 2 / 3 of the depth of the heat source well from the wellhead, the outlet pipe section is connected to the top end of the inner heat preservation tube, the inlet pipe section is in communication with the wall of the outer casing outside the heat source well, and the outlet pipe section and the inlet pipe section are used to be connected to the evaporator side of a ground source heat pump unit, and the heat circulation pipe connects the middle positions of the outlet pipe section and the inlet pipe section.

[0007] Compared with the prior art, the present application has the following beneficial effects:

[0008] 1. Promoting heat recovery: due to the higher temperature of deep geothermal and the lower temperature of shallow geothermal, the fluid in the heat exchanger of the present application is subjected to the action of thermal buoyancy, and through the arrangement of the heat circulation hole and the heat circulation pipe, two natural circulations of the upper part and the lower part are formed, which can accelerate the heat recovery speed and degree of the whole geothermal around the heat exchanger compared with no heat supplement;

[0009] 2. Stable energy efficiency: after the non-heating period ends, the temperature recovery degree of the geothermal around the heat exchanger of the present application is higher, which is beneficial to improve the heat extraction amount and the average temperature of the evaporator side, and maintain the high energy efficiency of long-term operation of the system;

[0010] 3. Zero energy consumption: the heat recovery of the geothermal body is promoted through natural circulation, which does not consume energy and significantly reduces the energy consumption and cost of system operation;

[0011] 4. High economic efficiency: the cost of adding the heat circulation pipe and the heat circulation hole is very low, which has almost no influence on the construction cost of the system, and the economic feasibility is relatively high. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a structural schematic view of the casing heat exchanger of the present application.

[0013] In the figure: 1 outer casing, 2 inner heat preservation tube, 3 heat circulation hole, 4 water suction tube, 5 outlet pipe section, 6 heat circulation pipe, 7 inlet pipe section. DETAILED DESCRIPTION

[0014] The technical solutions in the present application will be described clearly and completely in the embodiments of the present application with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative efforts belong to the scope of the present application.

[0015] Referring to Figure 1 As shown in the figure, a casing heat exchanger for promoting geotechnical heat recovery through natural circulation comprises an outer casing 1, an inner heat preservation pipe 2, a heat circulation hole 3, a water suction pipe 4, an outlet pipe section 5, a heat circulation pipe 6 and an inlet pipe section 7.

[0016] The outer casing 1 is filled with cement between the heat source well and the drilling gap, and the top end and the bottom end of the outer casing 1 are closed. The outer casing 1 is a J-55 oil casing with an outer diameter of 177.8 mm and a wall thickness of 9.19 mm.

[0017] The inner heat preservation pipe 2 is coaxially arranged inside the outer casing 1, and the bottom end of the inner heat preservation pipe 2 is connected to the water suction pipe 4 and spaced from the bottom end of the outer casing 1. The top end of the inner heat preservation pipe 2 extends out of the top end of the outer casing 1 and is connected and fixed thereto. The inner heat preservation pipe 2 is a PERT-II type heat preservation pipe with an outer diameter of 110 mm and a wall thickness of 10 mm.

[0018] The heat circulation hole 3 has a plurality of openings vertically spaced on the pipe wall of the inner heat preservation pipe 2. Under the condition of ensuring the strength of the inner heat preservation pipe 2, the total opening area of the heat circulation hole 3 is 3.14-4.00 cm 2 The upper edge of the uppermost opening of the heat circulation hole 3 is 2 / 3 of the depth of the heat source well from the wellhead.

[0019] The water suction pipe 4 is densely provided with a plurality of water inlet holes.

[0020] The outlet pipe section 5 is connected to the top end of the inner heat preservation pipe 2, and the inlet pipe section 7 is in communication with the pipe wall outside the heat source well. The outlet pipe section 5 and the inlet pipe section 7 are used to be connected to the evaporator side of the ground source heat pump unit to form a heat extraction cycle in the heating period. The outlet pipe section 5 and the inlet pipe section 7 are both seamless steel pipes with a pipe diameter of DN100.

[0021] The heat circulation pipe 6 connects the middle positions of the outlet pipe section 5 and the inlet pipe section 7. The heat circulation pipe 6 has a pipe diameter of DN20 and the same material as the outlet pipe section 5 and the inlet pipe section 7.

[0022] The specific principle and process of the present application are as follows:

[0023] By setting the heat circulation pipe 6 between the inlet pipe section 7 and the outlet pipe section 5, and setting the heat circulation hole 3 on the inner insulation pipe 2, the fluid in the pipe-in-pipe heat exchanger in the non-heating period forms two natural circulations of upper and lower parts under the action of thermal buoyancy.

[0024] In the heating period, the fluid circulation path is shown by the dotted arrows in the figure: Figure 1

[0025] In the heating period, the fluid circulation path is shown by the dotted arrows in the figure:

[0026] In the non-heating period, the fluid circulation path is shown by the solid arrows in the figure: Figure 1

[0027] For the upper 2 / 3 part of the fluid, i.e. the part with shallow heat circulation hole 3, the fluid in the annular cavity is initially in a static state, but due to the existence of the geothermal gradient, the fluid temperature near the heat circulation hole 3 in the annular cavity is higher than the temperature at the wellhead, and under the action of thermal buoyancy, the fluid begins to flow upwards. In the process of flowing upwards, the surrounding rock temperature drops, the fluid heat is dissipated to the surrounding rock, the fluid temperature drops, and the rock temperature rises. The lower temperature fluid in the upper part of the inner insulation pipe 2 and the annular cavity flows downward through the inner insulation pipe 2. The flow of natural circulation is very small, and the resistance of the fluid in the inner insulation pipe 2 to continue to flow downward at the heat circulation hole 3 is greater than the resistance of the fluid to return to the annular cavity through the heat circulation hole 3, so the upper fluid mainly returns to the outer sleeve 1 through the heat circulation hole 3. Therefore, under the action of thermal buoyancy, the upper 2 / 3 part of the fluid forms a natural circulation through the outer sleeve 1, the inlet pipe section 7, the heat circulation pipe 6, the outlet pipe section 5, the inner insulation pipe 2 and the heat circulation hole 3.

[0028] For the lower 1 / 3 part of the fluid, i.e. the part with deep heat circulation hole 3, the fluid temperature at the bottom of the annular cavity is higher than the temperature near the heat circulation hole 3, and under the action of thermal buoyancy, the fluid forms a natural circulation through the outer sleeve 1, the heat circulation hole 3, the inner insulation pipe 2 and the water suction pipe 4, and the temperature of the upper layer of rock will gradually rise.

[0029] ​​Therefore, the overall heat recovery speed of the surrounding rock and soil of the double pipe heat exchanger is accelerated, so that a higher heat extraction amount is maintained in the next heating period, mainly applied to the buried pipe heat exchange of the medium deep ground source heat pump system, the heat recovery of the rock and soil is accelerated through natural circulation, the heat attenuation of the rock and soil is delayed, which is beneficial to maintain long-term high-efficiency operation of the system, and has important significance for prolonging the service life of the system and reducing the operation energy consumption.

[0030] It is apparent to those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and that the application can be implemented in other embodiments without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. No reference signs in the claims should be considered as limiting the scope of the claims to the features to which the reference signs are attached.

[0031] Furthermore, it should be understood that although the present specification is described in terms of embodiments, not every embodiment according to the present specification need necessarily include every independent technical feature mentioned in the specification, and that reference to a particular feature of the specification does not mean that every embodiment according to the present specification necessarily includes that particular feature. The description of the embodiments is merely exemplary in nature and is in no way intended to limit the application, its application, or products by the application.

Claims

1. A pipe-in-pipe heat exchanger to promote geothermal heat recovery by natural circulation, characterized in that: The application relates to a heat source well for a ground source heat pump, which comprises an outer sleeve (1), an inner heat preservation pipe (2), heat circulation holes (3), a water absorbing pipe (4), an outlet pipe section (5), a heat circulation pipe (6) and an inlet pipe section (7), the top end and the bottom end of the outer sleeve (1) are closed and extend into a heat source well, the inner heat preservation pipe (2) is coaxially arranged in the outer sleeve (1), the bottom end of the inner heat preservation pipe (2) is connected with the water absorbing pipe (4) and is spaced from the bottom end of the outer sleeve (1), the top end of the inner heat preservation pipe (2) extends out of the top end of the outer sleeve (1) and is connected and fixed with the top end, a plurality of heat circulation holes (3) are vertically spaced and arranged on the pipe wall of the inner heat preservation pipe (2), the upper edge of the uppermost opening of the heat circulation holes (3) is 2 / 3 of the depth of the heat source well from the well mouth, the outlet pipe section (5) is connected with the top end of the inner heat preservation pipe (2), the inlet pipe section (7) is in communication with the pipe wall of the outer sleeve (1) outside the heat source well, the outlet pipe section (5) and the inlet pipe section (7) are used for being connected with the evaporator side of a ground source heat pump unit, the heat circulation pipe (6) is used for connecting the middle positions of the outlet pipe section (5) and the inlet pipe section (7), under the condition of ensuring the strength of the inner heat preservation pipe (2), the total opening area of the heat circulation holes (3) is 3.14-4.00 cm 2 .

2. A pipe-in-pipe heat exchanger for promoting thermal recovery of rock soil by natural circulation according to claim 1, characterized in that: The outer sleeve (1) extends into the heat source well and is filled with cement between the drilling gap.

3. The pipe-in-pipe heat exchanger for promoting geothermal heat recovery by natural circulation according to claim 1, wherein: The outer sleeve (1) is made of J-55 oil casing, with an outer diameter of 177.8 mm and a wall thickness of 9.19 mm.

4. The pipe-in-pipe heat exchanger for promoting geothermal heat recovery by natural circulation according to claim 1, wherein: The inner heat preservation pipe (2) is made of PERT-II type heat preservation pipe, with an outer diameter of 110 mm and a wall thickness of 10 mm.

5. The pipe-in-pipe heat exchanger for promoting geothermal heat recovery by natural circulation according to claim 1, wherein: The outlet pipe section (5) and the inlet pipe section (7) are both made of seamless steel pipes with a pipe diameter of DN100.

6. A pipe-in-pipe heat exchanger for promoting thermal recovery of rock soil by natural circulation according to claim 5, characterized in that: The heat cycle pipe (6) has a pipe diameter of DN20 and is made of the same material as the outlet pipe section (5) and the inlet pipe section (7).

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