Coaxial split-flow cooperative heat exchange system and method suitable for single vertical deep well

Abstract

The application discloses a coaxial shunt heat exchange system and method suitable for a single vertical deep well, wherein the heat exchange system comprises a driving pump, an external heat transfer pipe, a plurality of heat insulation guide pipes and a liquid mixing regulator; the driving pump is arranged on the ground surface and is used for conveying heat collecting fluid into the external heat transfer pipe to perform flow heat exchange; the external heat transfer pipe is sleeved in a borehole of the single vertical deep well; the plurality of heat insulation guide pipes are sequentially coaxially sleeved in the external heat transfer pipe in a descending order of diameter, and sequentially increase in length, so as to form a downward flowing heat exchange channel and an upward flowing production channel; the liquid mixing regulator comprises a liquid mixer and a plurality of flow regulating valves; the plurality of flow regulating valves are respectively used for controlling branch flow of heat collecting fluid at different temperatures in different heat insulation guide pipes; and the liquid mixer is used for mixing the plurality of branch flows. The heat exchange system is simple in structure and easy to construct, and can flexibly adjust the temperature of the heat collecting fluid.

Description

Technical Field

[0001] This invention relates to the field of geothermal energy, and more particularly to a coaxial split-flow synergistic heat exchange system and method suitable for a single vertical deep well. Background Technology

[0002] Utilizing underground heat exchange pipes to extract geothermal energy is one of the most mature geothermal extraction technologies currently available. Vertical coaxial deep-hole geothermal wells offer advantages such as structural stability, safe operation, and mature supporting technologies. A vertical coaxial deep-hole geothermal well consists of two parts: an outer pipe and an inner pipe. The outer pipe is responsible for transferring heat and is typically made of materials with high thermal conductivity. The inner pipe organizes the flow of the heat-collecting fluid and is typically made of materials with good insulation properties. During operation, the fluid flows downwards through the annular channel between the inner and outer pipes from the surface inlet to collect heat from the formation. It is then extracted to the surface through the bottom of the inner pipe for utilization. Related research indicates that, under certain structural and operational conditions, the extracted fluid temperature is determined by the heat-collecting flow rate; reducing the flow rate helps increase the extracted fluid temperature, and vice versa (see Yildirim N, Parmanto S, Akkurt GG. Thermodynamic assessment of downhole heat exchangers for geothermal powergeneration. Renewable Energy 2019;141:1080-1091). This means that when the total flow rate of the heating fluid is constant, the temperature of the extracted fluid from traditional vertical coaxial deep-hole geothermal wells lacks flexible self-regulation capability and cannot meet the dynamic changes in the heating demand of heat users as the required heating temperature changes with the external air temperature.

[0003] The present invention aims to address the challenges of existing technologies by designing a novel underground coaxial heat exchange structure and its associated operating mode. This structure should be designed to more efficiently organize the heat extraction process of pipeline fluid under the linear heating boundary of the formation, given a fixed total flow rate of the heating fluid. It should also enable flexible production temperature control, improve the temperature matching characteristics between the heat well and the heat user, and simultaneously meet the requirements of simple structure and ease of construction. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to propose a coaxial flow-splitting and collaborative heat exchange system suitable for single vertical deep wells, thereby improving the dynamic control capability of the produced temperature of the heat-harvested fluid under constant injection flow conditions in a single well.

[0005] The technical solution adopted in this invention is:

[0006] A coaxial split-flow synergistic heat exchange system suitable for a single vertical deep well is provided, including a drive pump, an external heat transfer pipe, a No. I insulated flow guide pipe, a No. II insulated flow guide pipe, a No. III insulated flow guide pipe, and a liquid mixing regulator:

[0007] A drive pump, located on the ground surface, delivers heat-collecting fluid into the external heat transfer pipe for flow heat exchange.

[0008] An external heat transfer pipe is installed inside the wellbore of a single vertical deep well to absorb formation heat and heat the heat-collecting fluid.

[0009] The diameters of the No. I, No. II, and No. III heat-insulating guide pipes decrease sequentially, while their lengths increase sequentially. They are coaxially fitted inside the external heat transfer pipe in order of decreasing diameter, forming a downward-flowing heat exchange channel and an upward-flowing extraction channel.

[0010] The liquid mixing regulator includes a liquid mixer and multiple flow control valves. The multiple flow control valves control the branch flow rates of the heat-collecting fluid at different temperatures in different insulated guide pipes; the liquid mixer mixes the multiple branch flow rates.

[0011] Following the above technical solution, the length of the external heat transfer pipe is consistent with the wellbore depth of a single vertical deep well.

[0012] Following the above technical solution, the length difference between the No. III heat-insulating guide pipe and the external heat transfer pipe is less than or equal to 1000 mm.

[0013] According to the above technical solution, the thermal conductivity of the external heat transfer tube is greater than or equal to 50 W / (m·K).

[0014] According to the above technical solution, the thermal conductivity of heat-insulating pipe I, heat-insulating pipe II, and heat-insulating pipe III is less than or equal to 0.05 W / (m·K).

[0015] Following the above technical solution, the outer diameter of the external heat transfer pipe is close to the inner diameter of the wellbore of a single vertical deep well.

[0016] Following the above technical solution, the output ends of each heat-insulated guide pipe are connected to the liquid mixer through different pipes located on the ground, and the flow regulating valve is installed on the corresponding pipe.

[0017] According to the above technical solution, the outer diameter of the No. I heat-insulating guide pipe is greater than half the inner diameter of the external heat transfer pipe and less than the inner diameter of the external heat transfer pipe; the outer diameter of the No. II heat-insulating guide pipe is greater than half the inner diameter of the No. I heat-insulating guide pipe and less than the inner diameter of the No. I heat-insulating guide pipe; the outer diameter of the No. III heat-insulating guide pipe is greater than half the inner diameter of the No. II heat-insulating guide pipe and less than the inner diameter of the No. II heat-insulating guide pipe.

[0018] This invention also provides a coaxial flow-splitting collaborative heat exchange method suitable for a single vertical deep well. This method, based on the coaxial flow-splitting collaborative heat exchange system for a single vertical deep well described above, includes the following steps:

[0019] When the heating fluid needs to be raised or lowered to the target heating temperature under the condition that the total flow rate remains constant, the first branch flow coefficient β1 of the No. I insulated guide pipe is set, and a series of branch flow coefficients (β1, β2, β3) that meet the target heating temperature T are calculated using the relationship between the branch flow coefficients; β2 is the second branch flow coefficient corresponding to the No. II insulated guide pipe, and β3 is the third branch flow coefficient corresponding to the No. III insulated guide pipe.

[0020] Calculate the flow power consumption of a series of branch flow coefficient groups that meet the target heating temperature, and use optimization algorithms to select the best solution among several branch flow coefficient groups with the goal of minimizing the flow power consumption of the overall heating process.

[0021] Adjust the corresponding flow regulating valve of each heat insulation guide pipe to control the corresponding branch flow rate, so that it matches the branch flow rate coefficient group of the optimal scheme;

[0022] By mixing the multiple branch flow rates, the heating fluid at the target heating temperature is obtained.

[0023] Following the above technical solution, specifically based on the Darcy-Weisbach equation, the pressure drop of each section is obtained by using the resistance coefficient, density, flow distance, flow velocity and hydraulic diameter of the heat-collecting fluid, and then combined with the flow rate to solve the flow power consumption corresponding to a series of branch flow coefficient groups.

[0024] The beneficial effects of this invention are as follows: This invention forms a downward-flowing heat exchange channel and an upward-flowing extraction channel by setting coaxial external heat transfer pipes and multiple heat-insulated guide pipes of different lengths and diameters inside a single vertical deep well. The branch flow rates of the heat-collecting fluids at different temperatures in different heat-insulated guide pipes are controlled by multiple flow regulating valves, thereby flexibly adjusting the temperature of the mixed heat-collecting fluids. In addition, this heat exchange system has the advantages of simple structure and easy construction.

[0025] Furthermore, based on the fact that the heat exchange system can control the flow of multiple branches from different depths during the heat extraction process under the condition of constant total flow of heat extraction fluid, the proportion of multiple heat fluids with different temperatures in the mixing process can be changed to achieve self-regulation of heating temperature. This can minimize the flow power consumption in the heat extraction process and improve the output temperature flexibility of the single vertical deep well heat extraction process.

[0026] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is an overall schematic diagram of a single vertical deep well coaxial diversion and collaborative heat recovery system according to an embodiment of the present invention;

[0029] Figure 2 This is a simplified longitudinal cross-sectional view of an underground coaxially fitted external heat transfer pipe and heat insulation guide pipe according to an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the upper cross section of an underground coaxially sleeved pipe according to an embodiment of the present invention;

[0031] Figure 4 This is a schematic diagram of the middle section of an underground coaxially sleeved pipe according to an embodiment of the present invention;

[0032] Figure 5 This is a schematic diagram of the lower cross section of an underground coaxially sleeved pipe according to an embodiment of the present invention;

[0033] Figure 6 This is a schematic diagram of a method for controlling heating temperature under constant total flow rate according to an embodiment of the present invention;

[0034] Figure 7 This is a comparison chart of the fluid heating temperature range between Embodiment 1 and the control example of the present invention;

[0035] Figure 8 This refers to a series of flow coefficients that satisfy a specified heating temperature in Embodiment 1 of the present invention;

[0036] Figure 9 The flow coefficient set that satisfies the specified heating temperature is selected by the optimization algorithm in Embodiment 1 of the present invention with the goal of minimizing flow power consumption;

[0037] In the picture:

[0038] 1. Drive pump; 2. Flow regulating valve; 3. Liquid mixer; 4. Surface connection pipe; 5. External heat transfer pipe; 6. No. I heat-insulating guide pipe; 7. No. II heat-insulating guide pipe; 8. No. III heat-insulating guide pipe. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] It should be noted that the illustrations provided in the embodiments of the present invention are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation. In actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0041] In this invention, it should also be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used only for descriptive and distinguishing purposes and should not be construed as indicating or implying relative importance.

[0042] Furthermore, it should be noted that the features of the various embodiments of the present invention can be combined or integrated in whole or in part, and as those skilled in the art will understand, they can interact and operate in different ways. Each embodiment can be implemented independently of each other or in association with one another.

[0043] like Figure 1 The diagram shown is an overall schematic of the single vertical deep well coaxial diversion and coordinated heat exchange system of the present invention. The overall heat extraction system includes a drive pump 1, an external heat transfer pipe 5, a No. I insulated guide pipe 6, a No. II insulated guide pipe 7, a No. III insulated guide pipe 8, and a liquid mixing regulator.

[0044] The drive pump 1 is located on the surface and transports the heat-collecting fluid into the external heat transfer pipe 5 for flow heat exchange. The external heat transfer pipe 5 is installed in the wellbore of a single vertical deep well to absorb formation heat and heat the heat-collecting fluid.

[0045] The diameters of the No. 1 heat-insulating guide pipe 6, the No. 2 heat-insulating guide pipe 7, and the No. 3 heat-insulating guide pipe 8 decrease sequentially, while their lengths increase sequentially. They are coaxially fitted inside the external heat transfer pipe 5 in order of decreasing diameter, forming a downward-flowing heat exchange channel and an upward-flowing extraction channel.

[0046] The liquid mixing regulator includes a liquid mixer 3 and multiple flow regulating valves 2. The multiple flow regulating valves 2 control the branch flow rates of the heat-collecting fluid at different temperatures in different insulated guide pipes respectively; the liquid mixer 3 mixes the multiple branch flow rates.

[0047] Specifically, the drive pump 1 can pump the heat-collecting fluid to the external heat transfer pipe 5 via the surface connection pipe 4. The heat-collecting fluid flows along... Figure 1 The heat-collecting fluid flows in the direction indicated by the middle arrow and absorbs heat from the outside. When the heat-collecting fluid flows to the bottom of the No. 1 insulated guide pipe 6, the fluid temperature rises to T1. A portion of the total flow rate m1 (m1=m·β1) is drawn upwards to the ground surface through the No. 1 insulated guide pipe 6. The remaining heat-collecting fluid continues to flow downwards along the inner wall of the external heat transfer pipe 5, absorbing heat and rising to T2 at the bottom of the No. 2 insulated guide pipe 7. A portion of this flow rate m2 (m2=m·β2) is drawn upwards to the ground surface at this point. The remaining heat-collecting fluid with a flow rate of m3 (m3=m·β3) flows downwards along the outer... The heat transfer pipe 5 flows downward to the bottom and is heated to T3 at the bottom of the No. III heat-insulating guide pipe 8 before being drawn to the ground surface. Multiple streams of extracted fluid with different temperatures and flow rates are transported to the liquid mixer 3 via the ground connection pipe 4. After thorough mixing, a heating fluid with a temperature of T and a total flow rate of m is produced to meet the needs of heat users. When the heat user's demand for heating temperature changes, the diversion and coordinated heating system of the present invention can dynamically adjust the temperature T of the heating fluid by changing the relative magnitude of the flow rates of each branch under the condition of constant total flow rate m.

[0048] Based on the coaxial split-flow coordinated heat exchange system applicable to a single vertical deep well based on the above embodiments, the present invention also provides a coaxial split-flow coordinated heat exchange method applicable to a single vertical deep well, comprising the following steps:

[0049] S1. Under the condition that the total flow rate remains unchanged, if it is necessary to raise or lower the heating fluid to the target heating temperature, set the first branch flow coefficient β1 of the No. I insulated guide pipe, and calculate a series of branch flow coefficients (β1, β2, β3) that meet the target heating temperature T using the relationship between the branch flow coefficients; β2 is the second branch flow coefficient corresponding to the No. II insulated guide pipe, and β3 is the third branch flow coefficient corresponding to the No. III insulated guide pipe.

[0050] S2. Calculate the flow power consumption of a series of branch flow coefficient groups that meet the target heating temperature. With the goal of minimizing the flow power consumption of the overall heating process, use optimization algorithms to select the best solution among several branch flow coefficient groups.

[0051] S3. Adjust the corresponding flow regulating valve of each heat insulation guide pipe to control the corresponding branch flow rate, so that it matches the branch flow rate coefficient group of the optimal scheme;

[0052] S4. Mix the multiple branch flow rates to obtain the heating fluid at the target heating temperature.

[0053] Specifically, when a heat user needs to raise / lower the heating temperature T, the output flow coefficient β1 of the No. 1 insulated guide pipe 6 is first set. Then, using the relationship between the flow coefficients of each branch (β1+β2+β3=1, β1T1+β2T2+β3T3=T), a series of flow coefficient sets (β1, β2, β3) that satisfy the target heating temperature T are obtained. This allows the flow velocity u of the heat-collecting fluid in each section of the wellbore to be determined. The Reynolds number Re is then calculated to determine the corresponding flow regime and the resistance coefficient f is calculated. Finally, the Darcy-Weisbach equation (Δp=fρLu) is used. 2 / 2 / d h Using the drag coefficient f, density ρ, flow distance L, flow velocity u, and hydraulic diameter d h The pressure drop Δp of each flow segment is obtained, and the flow power P corresponding to each flow coefficient group is solved by combining it with the flow rate. With the goal of minimizing the overall flow power consumption P in the heat extraction process, an optimization algorithm (such as a genetic algorithm) is used to select the optimal solution from several sets of flow coefficients that meet the requirements. Finally, the flow regulating valves 2 of each insulated guide pipe are adjusted to control the flow of the corresponding branch to match the optimal flow coefficient set. After the multiple branch flow streams are mixed, a heating fluid with a temperature of T is obtained. Thus, the heating temperature is dynamically adjusted under the condition that the total flow rate of the heat extraction fluid remains unchanged, so as to meet the heating / cooling needs of heat users. Figure 6 As shown.

[0054] In one specific embodiment of the present invention, the length of the external heat transfer tube is L. ex L ex The advantage of setting the external heat transfer pipe to the same depth as the wellbore is that it can make full use of the heat transfer area inside the wellbore and broaden the production temperature range of the heat-collecting fluid.

[0055] In one specific embodiment of the present invention, the pipe length of the No. III heat-insulating guide pipe 8 is L. in,III L in,III Less than the length L of the external heat transfer tube ex And L ex -L in,III ≤1000mm, its advantage is that this allows the fluid extracted through the No. III heat-insulating guide pipe 8 to absorb heat from the formation with a higher temperature, thereby increasing the upper limit of the mixing temperature of the heat extraction fluid.

[0056] In one specific embodiment of the present invention, the length of the No. I heat-insulating guide pipe 6 is L. in,I L in,I Less than L in,IIIFurthermore, it is set according to the minimum heating temperature and the corresponding stratum depth. Its advantage is that it can produce heat-collecting fluid that meets the minimum heating temperature requirement.

[0057] In one specific embodiment of the present invention, the length of the No. II heat-insulating guide pipe 7 is L. in,II L in,II Less than L in,III And greater than the above L in,I Its advantage is that it can produce heat-collecting fluid at intermediate temperatures.

[0058] In one specific embodiment of the present invention, the thermal conductivity of the external heat transfer tube is λ. ex , λ ex ≥50W / (m·K) has the advantage of reducing the thermal resistance between the formation and the heat extraction fluid, thereby increasing the heat transfer rate.

[0059] In one specific embodiment of the present invention, the thermal conductivity of each heat-insulating guide tube is λ. in , λ in The advantage of ≤0.05W / (m·K) is that it can suppress heat leakage of the fluid from the insulated guide pipe to the inside and outside, and increase the temperature of the fluid from the insulated guide pipe.

[0060] In one specific embodiment of the present invention, the outer diameter of the external heat transfer pipe 5 is D1, which is smaller than and as close as possible to the inner diameter of the wellbore. The advantage of this is that it can reduce the thermal resistance between the heat transfer pipe and the formation and improve the heat transfer rate of the external heat transfer pipe.

[0061] In a specific embodiment of the present invention, the outer diameters of the No. I heat-insulating guide pipe 6, the No. II heat-insulating guide pipe 7, and the No. III heat-insulating guide pipe 8 are D3, D5, and D7, respectively, and the inner diameters are D4, D6, and D8, respectively. The inner diameters of the external heat transfer pipe 5 are D2 and D3, which satisfy D2 / 2 < D3 < D2, D5, which satisfy D4 / 2 < D5 < D4, and D7, which satisfies D6 / 2 < D7 < D6. The advantage is that this can form three heat exchange sections: upper, middle, and lower, and avoid excessively high local flow velocities.

[0062] In a specific embodiment of the present invention, the total number of flow regulating valves 2 is consistent with the number of heat-insulating guide pipes, and they are respectively located at the rear end of the corresponding heat-insulating guide pipes. The advantage is that the branch flow rates of multiple fluids with different extraction temperatures can be controlled by adjusting the valves, so as to achieve dynamic regulation of the heating temperature of a single well under the condition of constant total inlet flow rate.

[0063] In a specific embodiment of the present invention, the control method of the flow coefficient of each branch of the heat-insulating guide pipe is derived based on the conservation of mass and energy, and is optimized with the flow power consumption of the heat extraction process as the target. Its advantage is that a series of branch flow coefficient groups that meet the target heating temperature can be obtained, and optimization algorithms are used to optimize each coefficient group to minimize the flow power consumption of the heat extraction process.

[0064] Example 1: Length L of external heat transfer pipe 5 ex The length L of the No. 1 heat-insulating guide pipe 6 is 2,000,000 mm. in,I The length L of the No. II heat-insulating guide pipe 7 is 1200000mm. in,II The length L of the No. III heat-insulating guide pipe 8 is 1600000mm. in,III It is 1999700mm, such as Figure 2 As shown; the outer diameter D1 of external heat transfer pipe 5 is 210mm and the inner diameter D2 is 200mm; the outer diameter D3 of insulation guide pipe I 6 is 160mm and the inner diameter D4 is 150mm; the outer diameter D5 of insulation guide pipe II 7 is 110mm and the inner diameter D6 is 100mm; the outer diameter D7 of insulation guide pipe III 8 is 60mm and the inner diameter D8 is 50mm. Figure 3 , Figure 4 and Figure 5 As shown; the thermal conductivity of the external heat transfer pipe 5 is 60 W / (m·K), and the thermal conductivity of the No. I heat-insulating flow guide pipe 6, the No. II heat-insulating flow guide pipe 7, and the No. III heat-insulating flow guide pipe 8 is 0.002 W / (m·K); each heat-insulating flow guide pipe is equipped with a flow regulating valve to control the flow of the corresponding branch.

[0065] Comparative example: The main parameters are the same as in Example 1, except that there is only one heat-insulated flow guide pipe, no heat-insulated flow guide pipe flow regulating valve, no liquid mixer and corresponding connecting pipe, that is, the traditional coaxial sleeve structure.

[0066] Using the energy conservation equation for the heat-harvesting fluid in the wellbore, the thermal resistance formula for the circular pipe wall, and the convective heat transfer correlation formula for annular and circular cross-section flow channels, simulation tests were conducted on the heat generation and flow performance of Example 1 and the reference example under the same injection flow rate and injection temperature. The results are as follows: Figure 7-9 As shown.

[0067] Figure 7The diagram shows the controllable range of heating temperature T for Example 1 and the control example during operation. The results show that, because Example 1 uses multiple insulated diversion pipes of different lengths to divert and extract the heat-collecting fluid at different depths within the well, the temperature T of the mixed heating fluid is jointly determined by the first stream of heat-collecting fluid (flow rate m1, temperature T1) extracted by insulated diversion pipe 6 (I), the second stream of heat-collecting fluid (flow rate m2, temperature T2) extracted by insulated diversion pipe 7 (II), and the third stream of heat-collecting fluid (flow rate m3, temperature T3) extracted by insulated diversion pipe 8 (III).

[0068] Figure 7 The results show that, since the control example (traditional coaxial sleeve structure) does not have the ability to divert heat using flow distribution, its heating temperature cannot be adjusted under the condition of constant injection flow. In contrast, in Example 1, as the diversion coefficient β1 of the No. I insulated guide pipe 6 gradually increases from 0 to 1, and the diversion coefficient β2 of the No. II insulated guide pipe 7 is 0, the dominant fluid in the liquid mixer 3 transitions from the third hot fluid extracted from a deeper depth to the first hot fluid extracted from a shallower depth. Therefore, the final heating temperature after fluid mixing can be flexibly adjusted between the lowest temperature of 55°C and the highest temperature of 78°C. The change in the relative magnitude of the branch flow allows the heating temperature of a single vertical deep well to be autonomously controlled according to user needs under the condition of constant total flow, making the heat production performance more flexible.

[0069] Figure 8 The diagram shows a series of flow coefficients (β1, β2, β3) obtained when the heating temperature changes, as shown in Example 1. The obtained coefficient set simultaneously satisfies the governing equations for mass and energy conservation. Since these equations are planar in three-dimensional space, the intersection of the mass conservation plane and the energy conservation plane, along with boundary constraints, yields the result. Figure 8 The solution set of flow coefficients for a specified heating temperature is shown. Figure 8 The results show that when the flow coefficient set meets any one of the values ​​from (0.0000, 0.7787, 0.2213) to (0.3776, 0.0000, 0.6224), each branch flow can produce a heating fluid at a temperature of 70°C after thorough mixing, thus limiting the range for screening the optimal flow coefficient set.

[0070] Figure 9 The diagram shows the flow power consumption corresponding to each flow coefficient group for achieving a specified heating temperature, as well as the optimal coefficient group selected by the algorithm. Since fluid flow during heat extraction requires energy to drive the pump, and the branch flow rate and resistance in different sections change with the variation of the flow coefficient group, pump power consumption is a crucial indicator for actual operation. By using an optimization algorithm to select the optimal flow coefficient group that meets the requirements, the flow coefficient group with the minimum flow power consumption can be obtained. Figure 9The results show that, for Example 1, the heat collection flow power consumption is minimized when the flow coefficient group is (0.1100, 0.5519, 0.3381). Therefore, this flow coefficient group is the optimal flow distribution relationship, and the corresponding insulated flow guide pipe flow valve can be adjusted accordingly to achieve dynamic adjustment of heat collection temperature in the most energy-efficient way.

[0071] In summary, this invention achieves split-flow synergistic heat extraction in a single vertical deep well by coaxially installing multiple insulated guide pipes of different diameters and lengths within a single vertical deep well, and by employing a flow coefficient group calculation method, a flow regulating valve, and a liquid mixer. An algorithm is used to select the optimal flow coefficient group that meets the conditions, thereby enabling more full and effective utilization of the heat transfer area of ​​the wellbore's inner wall and providing flexible dynamic control over the heating temperature of the heat extraction fluid under constant injection flow conditions.

[0072] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0073] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0074] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A coaxial split-flow synergistic heat exchange system suitable for a single vertical deep well, characterized in that, Includes a drive pump, external heat transfer pipes, insulated guide pipe I, insulated guide pipe II, insulated guide pipe III, and a liquid mixing regulator: A drive pump, located on the ground surface, delivers heat-collecting fluid into the external heat transfer pipe for flow heat exchange. An external heat transfer pipe is installed inside the wellbore of a single vertical deep well to absorb formation heat and heat the heat-collecting fluid. The diameters of the No. I, No. II, and No. III heat-insulating guide pipes decrease sequentially, while their lengths increase sequentially. They are coaxially fitted inside the external heat transfer pipe in order of decreasing diameter, forming a downward-flowing heat exchange channel and an upward-flowing extraction channel. The liquid mixing regulator includes a liquid mixer and multiple flow control valves, which control the branch flow rates of the heat-collecting fluid at different temperatures in different insulated guide pipes. A liquid mixer combines multiple branch flows.

2. The coaxial split-flow synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The length of the external heat transfer pipe is consistent with the wellbore depth of a single vertical deep well.

3. The coaxial flow-diverting synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The length difference between the No. III heat-insulating guide pipe and the external heat transfer pipe is less than or equal to 1000 mm.

4. The coaxial flow-distribution synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The thermal conductivity of the external heat transfer tube is greater than or equal to 50 W / (m·K).

5. The coaxial flow-distribution synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The thermal conductivity of insulated flow guide tubes I, II, and III is less than or equal to 0.05 W / (m·K).

6. The coaxial flow-distribution synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The outer diameter of the external heat transfer pipe is close to the inner diameter of the wellbore of a single vertical deep well.

7. The coaxial flow-splitting and synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The output ends of each insulated flow guide pipe are connected to the liquid mixer through different pipes located on the ground, and the flow regulating valve is set on the corresponding pipe.

8. The coaxial flow-splitting and synergistic heat exchange system suitable for a single vertical deep well according to claim 1, characterized in that, The outer diameter of heat-insulating pipe I is greater than half the inner diameter of the external heat transfer pipe and less than the inner diameter of the external heat transfer pipe; the outer diameter of heat-insulating pipe II is greater than half the inner diameter of heat-insulating pipe I and less than the inner diameter of heat-insulating pipe I; the outer diameter of heat-insulating pipe III is greater than half the inner diameter of heat-insulating pipe II and less than the inner diameter of heat-insulating pipe II.

9. A coaxial flow-splitting synergistic heat transfer method suitable for a single vertical deep well, characterized in that, This method, based on any one of claims 1-8, is a coaxial flow-splitting synergistic heat exchange system suitable for a single vertical deep well, and includes the following steps: When the heating fluid needs to be raised or lowered to the target heating temperature under the condition that the total flow rate remains constant, the first branch flow coefficient β1 of the No. I insulated guide pipe is set, and a series of branch flow coefficients (β1, β2, β3) that meet the target heating temperature T are calculated using the relationship between the branch flow coefficients; β2 is the second branch flow coefficient corresponding to the No. II insulated guide pipe, and β3 is the third branch flow coefficient corresponding to the No. III insulated guide pipe. Calculate the flow power consumption of a series of branch flow coefficient groups that meet the target heating temperature, and use optimization algorithms to select the best solution among several branch flow coefficient groups with the goal of minimizing the flow power consumption of the overall heating process. Adjust the corresponding flow regulating valve of each heat insulation guide pipe to control the corresponding branch flow rate, so that it matches the branch flow rate coefficient group of the optimal scheme; By mixing the multiple branch flow rates, the heating fluid at the target heating temperature is obtained.

10. The coaxial flow-splitting and synergistic heat transfer method applicable to a single vertical deep well according to claim 9, characterized in that, Specifically, based on the Darcy-Weisbach equation, the pressure drop of each flow segment is obtained by using the resistance coefficient, density, flow distance, flow velocity and hydraulic diameter of the heat-collecting fluid, and then combined with the flow rate to solve the flow power consumption corresponding to a series of branch flow coefficient groups.

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