A medium-deep three-layer casing coaxial geothermal utilization device for combined heat and cold extraction

Abstract

A mid-deep three-layer casing coaxial geothermal utilization device for integrated heating and cooling, comprising a heating outer casing, a cooling outer casing, an upper inner casing, and a lower inner casing disposed within the heating outer casing; the bottom end of the upper inner casing and the top end of the lower inner casing are connected via an electromagnetic four-way valve; the electromagnetic four-way valve controls the flow between the upper inner casing and the cooling outer casing via valve one, and controls the flow between the upper inner casing and the lower inner casing via valve two; a heating outer casing inlet is provided at the top end of the heating outer casing; a cooling outer casing outlet is provided at the top end of the cooling outer casing; an inner casing inlet / outlet is provided at the top end of the upper inner casing; the inner casing inlet / outlet serves as an outlet in heating operation and as an inlet in cooling operation. The present invention can extract heat and store cold in winter and extract cold and store heat in summer, thereby achieving sustainable utilization of mid-deep geothermal resources and improving the heating capacity of the ground heating system.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal resource utilization, and in particular relates to a mid-deep layer three-layer casing coaxial geothermal utilization device that integrates heat and cold extraction. Background Art

[0002] As a green, low-carbon, recyclable, and renewable resource, geothermal energy has large reserves and a wide distribution, making its utilization of great significance, especially for medium- and deep-layer geothermal energy at depths of more than 2 km. Medium- and deep-layer geothermal rock refers to dense, impermeable hot rock masses with little or no fluid, which are prevalent deep within the earth's strata. Its reserves are extremely rich, equivalent to 30 times the energy contained in the world's oil, natural gas, and coal. Due to various potential problems with ground-source heat pumps, including groundwater loss and water pollution, imbalance in hot and cold loads that affects the next year's use, and high corrosion resistance requirements for heat exchangers, resulting in increased costs and shortened lifespans, the current widespread use of "heat extraction without water extraction" medium- and deep-layer geothermal energy non-interference clean heating technology uses coaxial sealed casing downhole heat exchange to achieve "low-impact development and high-efficiency utilization" of geothermal resources.

[0003] However, the current medium-deep coaxial casing heat extraction technology still has some problems: 1) Heat extraction performance degradation. During actual operation, due to the continuous extraction of heat from the formation, the imbalance of hot and cold loads causes the underground temperature level to drop rapidly, the heat exchanger's heat extraction performance to decline, and the overall heat extraction device power to decay; 2) The utilization rate of geothermal wells is not high. The drilling and construction costs of geothermal wells and equipment are relatively high. However, in actual operation, it is limited by the heating cycle and performance degradation. It can only operate effectively for 4 months each year, and the utilization efficiency of medium-deep geothermal equipment is low. Therefore, it is necessary to propose a new medium-deep geothermal utilization device that can realize the alternating input of heat load and cold load to the formation to maintain a high underground temperature level and thus maintain a high continuous heat exchange performance of the geothermal utilization device. By increasing the cooling benefits in summer and improving the heating benefits in winter, geothermal energy can be further developed and utilized and its economic benefits can be improved. Summary of the Invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a medium-deep three-layer casing coaxial geothermal utilization device that integrates heating and cooling. By adding a cooling outer casing and an electromagnetic four-way valve, and changing the heating outer casing to a variable diameter casing, and changing the insulation inner casing to a two-stage type, the medium-deep underground coaxial heat exchanger is changed to a three-layer casing coaxial heat exchanger, and the flow channel changes are controlled to achieve heating in winter and cooling in summer. The heating performance of the device is improved by alternating ground temperature compensation and a cooling operating condition is added, so as to realize efficient and sustainable utilization of medium-deep geothermal resources and improve the economic benefits of the system.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A mid-deep three-layer casing coaxial geothermal utilization device for integrated heating and cooling, comprising a heating outer casing, a cooling outer casing, an upper inner casing, and a lower inner casing disposed within the heating outer casing, wherein the bottom end of the cooling outer casing is sealed and connected to the outer wall of the upper inner casing or the outer wall of the lower inner casing, and the bottom end of the lower inner casing is open and suspended in the air;

[0007] The bottom end of the upper inner casing and the top end of the lower inner casing are connected by an electromagnetic four-way valve; the electromagnetic four-way valve controls the flow path between the upper inner casing and the cooling outer casing through valve one, and controls the flow path between the upper inner casing and the lower inner casing through valve two;

[0008] A heating outer sleeve inlet is provided at the top of the heating outer sleeve; a cooling outer sleeve outlet is provided at the top of the cooling outer sleeve; an inner sleeve inlet / outlet is provided at the top of the upper inner sleeve; the inner sleeve inlet / outlet is an outlet under heating conditions and an inlet under cooling conditions.

[0009] In one embodiment, the heat extraction outer casing, the cooling outer casing and the upper inner casing form a three-layer casing for achieving heat exchange in cooling conditions;

[0010] The heat extraction outer casing, the upper inner casing and the lower inner casing form a double-layer casing for achieving heat exchange in a heat extraction working condition.

[0011] Under the heat extraction condition, the valve 1 is closed and the valve 2 is opened, and the circulating water is injected from the heat extraction outer casing inlet, flows through the annular space, flows into the lower inner casing from the bottom end of the lower inner casing, then enters the upper inner casing through the valve 2, and finally flows out from the inner casing inlet / outlet;

[0012] Under the cooling condition, valve one is opened and valve two is closed. Circulating water is first filled into the outer casing for heating to transfer formation heat. When the cooling condition is in operation, circulating water is injected from the inlet / outlet of the inner casing, enters the outer casing for cooling through valve one, flows through the annular space, and then flows out from the outlet of the outer casing for cooling.

[0013] In one embodiment, under the cooling condition, circulating water is filled through the heat extraction outer casing inlet.

[0014] In one embodiment, the outer heating casing is a variable diameter oil casing or a steel pipe, the upper radius of which is larger than the lower radius and the upper length is smaller than the lower length. The outer cooling casing is arranged at the upper part of the inner heating casing.

[0015] In one embodiment, the cooling outer casing is an oil casing or a steel pipe.

[0016] In one embodiment, the upper inner casing and the lower inner casing are PPR pipes, PE-RT pipes or PB pipes, and the length of the upper inner casing is shorter than that of the lower inner casing.

[0017] In one embodiment, the first valve is placed on the side wall of the upper inner sleeve, and the second valve is placed inside the upper inner sleeve or the lower inner sleeve.

[0018] In one embodiment, the control switch of the electromagnetic four-way valve is placed in the wellhead equipment through a circuit connection.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention provides a medium-deep layer three-layer casing coaxial geothermal utilization device that integrates heating and cooling. By adding a cooling outer casing and an electromagnetic four-way valve, and changing the heating outer casing to a variable diameter casing and changing the insulation inner casing to a two-stage type, the medium-deep underground coaxial heat exchanger is changed to a three-layer casing coaxial heat exchanger, and the flow channel change is controlled to achieve heating in winter and cooling in summer. The cooling operation condition is added, so that the existing medium-deep heating technology that is in operation for 4 months and shut down for 8 months is changed to operating for 4 months in winter for heating and 4 months in summer for cooling, thereby increasing the operating income of the medium-deep layer geothermal utilization device.

[0021] (2) Based on the design of the present invention, a mid-deep three-layer casing coaxial geothermal utilization device with integrated heating and cooling is adopted. While adding cooling conditions, it adopts alternating operation of heating in winter and cooling in summer. It can realize alternating compensation recovery of underground temperature under the premise of taking heat and cooling without taking water, thereby improving the heating and cooling performance of the device when it is operated for many consecutive years and making more rational use of mid-deep geothermal energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the device of the present invention;

[0023] Figure 2 It is a structural schematic diagram of the device of the present invention under heat extraction working condition;

[0024] Figure 3 Schematic diagram of the structure of the device of the present invention under cooling conditions;

[0025] Figure 4 This is a schematic diagram of the structure of an existing medium-deep underground heat extraction device;

[0026] Figure 5 The relationship between the cooling power and the operating time of the device of the present invention under cooling conditions;

[0027] Figure 6The radial changes in soil temperature at 500 m underground after the existing medium-deep underground geothermal utilization device and the device of the present invention have been operated for one year and two years respectively.

[0028] Figure 7 This is a comparison chart of the heat extraction power versus operating time in the second year of operation of an existing medium-deep underground geothermal utilization device and the device of the present invention;

[0029] The numbers in the figure are: 1. Geothermal well, 2. Backfill material, 3. Remove the cold outer casing, 4. Remove the hot outer casing, 5. Upper inner casing, 6. Lower inner casing, 7. Solenoid four-way valve, 7-1. Valve one, 7-2. Valve two, 8. Inner casing inlet / outlet, 9. Remove the hot outer casing inlet, 10. Remove the cold outer casing outlet. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0031] The present invention aims to solve the problem of uneven cooling and heating loads in existing medium- and deep-level underground geothermal utilization devices, reduce geothermal losses and heating performance degradation caused by continuous operation, and improve operating benefits and the utilization rate of geothermal resources. It comprehensively considers indicators such as continuous operation heating power and geothermal distribution, and rationally designs a medium- and deep-level three-layer casing coaxial geothermal utilization device that integrates heating and cooling. It is expected that under the premise of taking heat and cooling without taking water, it can take heat and store cold in winter, and take cold and store heat in summer, and perform geothermal compensation through alternating operation of taking cooling and taking heat, thereby reducing the heating performance loss caused by continuous operation for many years, realizing the efficient and sustainable utilization of medium- and deep-level geothermal resources, and improving the heating capacity of the ground heating system.

[0032] refer to Figures 1 to 3 The device mainly includes a heating outer casing 4, a cooling outer casing 3, an upper inner casing 5 and a lower inner casing 6 arranged inside the heating outer casing 4, and an electromagnetic four-way valve 7 for controlling the flow between the upper inner casing 5 and the cooling outer casing 3, and the flow between the upper inner casing 5 and the lower inner casing 6 according to different working conditions. The control switch of the electromagnetic four-way valve 7 is placed in the well equipment through a circuit connection for easy operation.

[0033] The bottom end of the cooling outer casing 3 is sealed and connected to the outer wall of the upper inner casing 5 or the outer wall of the lower inner casing 6, while the bottom end of the lower inner casing 6 is left open and suspended. A solenoid four-way valve 7 is located at the junction of the bottom end of the upper inner casing 5 and the top end of the lower inner casing 6. It includes valve 1 7-1 and valve 2 7-2. Valve 1 7-1 is located on the side wall of the upper inner casing 5, and valve 2 7-2 is located inside the upper inner casing 5 or the lower inner casing 6.

[0034] A heating outer sleeve inlet 9 is provided at the top of the heating outer sleeve 4; a cooling outer sleeve outlet 10 is provided at the top of the cooling outer sleeve 3; an inner sleeve inlet / outlet 8 is provided at the top of the upper inner sleeve 5; the inner sleeve inlet / outlet 8 is an outlet under heating conditions and an inlet under cooling conditions.

[0035] In the above structure, the heating outer sleeve 4, the cooling outer sleeve 3 and the upper inner sleeve 5 can form a three-layer sleeve for realizing heat exchange in the cooling condition. Preferably, the three-layer sleeve is coaxial; accordingly, the heating outer sleeve 4 and the upper inner sleeve 5 and the lower inner sleeve 6 form a coaxial double-layer sleeve for realizing heat exchange in the heating condition. Preferably, the two layers of sleeve are coaxial.

[0036] To deploy the apparatus of the present invention, it is obviously necessary to set up a geothermal well 1, place a heat extraction outer casing 4 within the well, and place a certain amount of backfill material 2 on the wall of the well 1, with the backfill material 2 closely attached to the outer wall of the heat extraction outer casing 4. In other words, the backfill material 2 is filled between the heat extraction outer casing 4 and the geothermal well 1. The backfill material 2 can be directly made of the rock and soil obtained during drilling.

[0037] In one embodiment, the geothermal well 1 has a borehole diameter of 300 mm and a depth of 3,000 m. The heating outer casing 4 is a variable-diameter oil casing with an upper outer diameter of 247.22 mm, an inner diameter of 228.84 mm, and a length of 850 m; its lower outer diameter is 177.8 mm, an inner diameter of 159.42 mm, and a length of 2,150 m. The cooling outer casing 3 is an oil casing with an outer diameter of 177.8 mm, an inner diameter of 159.42 mm, and a length of 850 m. It is located in the upper or upper middle portion of the heating outer casing 4.

[0038] The upper inner casing 5 and the lower inner casing 6 can be arbitrarily selected from PPR pipes, PE-RT pipes or PB pipes, etc., with equal diameters. In this embodiment, PE-RTⅡ type is selected, with an outer diameter of 110mm and an inner diameter of 90mm. The length of the upper inner casing 5 is 850m, and the length of the lower inner casing 6 is 2150m. The two are connected and fixed by an electromagnetic four-way valve 7.

[0039] The device of the present invention adopts an alternating operation mode of operating in a heating condition for four months in winter and stopping for two months to restore the ground temperature, and operating in a cooling condition for four months in summer and stopping for two months to restore the ground temperature to achieve alternating ground temperature compensation;

[0040] When the heat extraction mode is in operation, the outside-in and inside-out operation mode is adopted. Specifically, the electromagnetic four-way valve 7 controls valve 1 7-1 to be closed and valve 2 7-2 to be opened. The circulating water is injected from the heat extraction outer casing inlet 9, flows through the annular space between the heat extraction outer casing 4 and the cold extraction outer casing 3 and the annular space between the heat extraction outer casing 4 and the lower section inner casing 6, and after sufficient heat exchange with the formation, flows from the bottom of the lower section inner casing 6 into the lower section inner casing 6, then enters the upper section inner casing 5 through valve 2 7-2, and finally flows out from the inner casing inlet / outlet 8, completing the outside-in and inside-out heat extraction. Figure 2 shown.

[0041] The cooling mode adopts the inside-out operation mode. Specifically, valve 7-1 is opened and valve 7-2 is closed. First, the annular space of the heating outer casing 4 is filled with filling water through the heating outer casing inlet 9 to realize heat exchange from the formation to the cooling outer casing 3. When the cooling mode is running, the circulating water is injected from the inner casing inlet / outlet 8, flows through the upper inner casing 5, and then enters the annular space of the cooling outer casing 3 through the valve 7-1. After exchanging heat with the filling water in the heating outer casing 4, it flows out from the cooling outer casing outlet 10, completing the inside-out cooling mode. Figure 3 shown.

[0042] The present invention adds a cooling outer sleeve 3 and an electromagnetic four-way valve 7 to the traditional medium-deep coaxial underground heat extraction device, changes the heating outer sleeve 4 into a variable diameter sleeve, and changes the insulation inner sleeve into a two-stage type (upper inner sleeve 5 and lower inner sleeve 6), thereby changing the medium-deep underground coaxial heat exchanger into a three-layer sleeve coaxial heat exchanger, controlling the flow channel change to achieve heating in winter and cooling in summer, and adding a cooling operating condition, so that the existing medium-deep heat extraction technology that is in operation for 4 months and shut down for 8 months is changed to heating for 4 months in winter and cooling for 4 months in summer, thereby increasing the operating income of the medium-deep geothermal utilization device; and based on the device of the present invention, while adding the cooling operating condition, the alternating operation of heating in winter and cooling in summer is adopted, which can realize the alternating compensation recovery of underground temperature under the premise of taking heat and cooling without taking water, thereby improving the heating and cooling performance of the device when it is operated for many years in a row, and making more reasonable use of medium-deep geothermal energy.

[0043] The device of the present invention was evaluated using numerical simulation. Numerical simulation analyzed the heat extraction power to evaluate the heat exchange performance of the medium- to deep-level underground heat exchanger. Ground temperature distribution simulation evaluated ground temperature recovery to determine whether it would affect continued operation in the second year. In the present embodiment, numerical simulations were conducted to compare the operation of a conventional medium- to deep-level underground heat extraction device with that of the present invention over two consecutive years.

[0044] Figure 4The structure of a conventional medium-deep underground heat extraction device is shown, sharing common components and dimensions with the device of the present invention. The inner casing of the present invention is divided into an upper inner casing 5 and a lower inner casing 6, while the inner casing of the conventional medium-deep underground heat extraction device consists of a 3000m long insulated pipe. In the examples, the simulated geothermal gradients of the conventional medium-deep underground heat extraction device and the device of the present invention are the same: a constant temperature layer of 7°C at a depth of 250m, and a variable temperature layer of 3.69°C / 100m at a depth of 2750m. The simulated inlet temperature for the heating condition is 3°C and the flow rate is 30t / h, while the simulated inlet temperature for the cooling condition of the present invention is 30°C and the flow rate is 10t / h.

[0045] Figure 5 The figure shows the relationship between the cooling power and operating time of the device under the cooling condition. As can be seen from the figure, even at a relatively low inlet temperature of 30°C and a small flow rate of 10 t / h, the device can still achieve a considerable cooling power after adding the cooling condition. This demonstrates the device's excellent cooling performance and can improve the economic benefits of medium- and deep-layer geothermal utilization devices by adding the cooling condition.

[0046] Figure 6 The radial variation in soil temperature at 500 meters below ground level after one and two years of operation for an existing medium- to deep-level geothermal utilization device and the device of the present invention, respectively. The figure shows that the ground temperature in the existing medium- to deep-level geothermal utilization device decreases year by year due to the continuous cooling load inputted into the ground by heat extraction, especially in the soil near the heat exchange well. However, the shallow soil temperature in the device of the present invention, due to the heat load inputted into the ground by summer cooling, is significantly higher than that of the existing medium- to deep-level geothermal utilization device. Furthermore, as the shallow soil temperature increases year by year due to the continuous summer cooling inputted into the shallow soil, the shallow soil temperature increases, especially in the soil near the heat exchange well.

[0047] Figure 7 This is a comparison chart of the heat extraction power versus operating time for an existing medium- to deep-level underground geothermal utilization device and the device of the present invention in the second year of operation. The chart shows that after one year of operation, the initial heat extraction power of the device of the present invention in the second year of operation was 951kW, and the heat extraction power after 30 days of operation was 726kW. The initial heat extraction power of the existing medium- to deep-level underground geothermal utilization device was 829kW, and the heat extraction power after 30 days of operation was 697kW. This indicates that the performance of the present invention is significantly improved compared to existing underground geothermal utilization devices due to the compensation of underground heat by the summer cooling condition.

[0048] In summary, the present invention designs a medium-deep three-layer casing coaxial geothermal utilization device that integrates heating and cooling. While adding a cooling working condition, it adopts alternating operation of heating in winter and cooling in summer. It can realize alternating compensation recovery of underground temperature under the premise of taking heat and cooling without taking water, thereby improving the heating and cooling performance of the device when it is operated for many consecutive years, making more rational use of medium-deep geothermal energy, and improving the economic benefits of the medium-deep geothermal utilization device.

Claims

1. A mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction, characterized in that: It comprises a heating outer sleeve (4), a cooling outer sleeve (3), an upper inner sleeve (5) and a lower inner sleeve (6) arranged inside the heating outer sleeve (4), wherein the bottom end of the cooling outer sleeve (3) is closed and connected to the outer wall of the upper inner sleeve (5) or the outer wall of the lower inner sleeve (6), and the bottom end of the lower inner sleeve (6) is open and suspended; The bottom end of the upper inner casing (5) and the top end of the lower inner casing (6) are connected via an electromagnetic four-way valve (7); the electromagnetic four-way valve (7) controls the on-off of the flow path between the upper inner casing (5) and the cooling outer casing (3) via valve 1 (7-1), and controls the on-off of the flow path between the upper inner casing (5) and the lower inner casing (6) via valve 2 (7-2); The top of the heat extraction outer sleeve (4) is provided with a heat extraction outer sleeve inlet (9); the top of the cooling outer sleeve (3) is provided with a cooling outer sleeve outlet (10); the top of the upper section inner sleeve (5) is provided with an inner sleeve inlet / outlet (8); the inner sleeve inlet / outlet (8) is an outlet in the heat extraction working condition and an inlet in the cooling working condition; Under the heat extraction condition, the valve 1 (7-1) is closed, the valve 2 (7-2) is opened, and the circulating water is injected from the heat extraction outer casing inlet (9), flows through the annular space, flows into the lower inner casing (6) from the bottom end, then enters the upper inner casing (5) through the valve 2 (7-2), and finally flows out from the inner casing inlet / outlet (8); In the cooling condition, valve 1 (7-1) is opened and valve 2 (7-2) is closed. Circulating water is firstly filled into the heat extraction outer casing (4) to transfer the formation heat. In the cooling condition, circulating water is then injected from the inner casing inlet / outlet (8), enters the cooling outer casing (3) through valve 1 (7-1), flows through the annular space, and then flows out from the cooling outer casing outlet (10).

2. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: The heat extraction outer casing (4), the cooling outer casing (3) and the upper inner casing (5) form a three-layer casing for realizing heat exchange in cooling conditions; The heat extraction outer casing (4), the upper inner casing (5) and the lower inner casing (6) form a double-layer casing for achieving heat exchange in a heat extraction working condition.

3. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: Under the cooling condition, circulating water is filled through the heat extraction outer casing inlet (9).

4. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: The heat extraction outer casing (4) is a variable diameter oil casing or a steel pipe, the upper radius of which is larger than the lower radius, and the upper length is smaller than the lower length. The cooling outer casing (3) is arranged at the upper part of the heat extraction outer casing (4).

5. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 or 4, characterized in that: The cooling outer casing (3) is an oil casing or a steel pipe.

6. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: The upper inner casing (5) and the lower inner casing (6) are PPR pipes, PE-RT pipes or PB pipes, and the length of the upper inner casing (5) is shorter than the length of the lower inner casing (6).

7. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: The valve 1 (7-1) is placed on the side wall of the upper inner sleeve (5), and the valve 2 (7-2) is placed inside the upper inner sleeve (5) or the lower inner sleeve (6).

8. The mid-deep three-layer casing coaxial geothermal utilization device for integrated heat and cold extraction according to claim 1 is characterized in that: The control switch of the electromagnetic four-way valve (7) is placed in the well equipment through a circuit connection.

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