Underground closed heat removal system, multi-energy complementary heating system and operation method of multi-energy complementary heating system

Abstract

The invention provides an underground closed heat removal system, a multi-energy complementary heating system and an operation method of the multi-energy complementary heating system, and relates to the technical field of renewable energy source utilization, the underground closed heat removal system comprises a porous rock stratum, a directional well pipe and high-conductivity cement, and a directional well hole is drilled in the porous rock stratum; the directional well hole comprises a vertical well hole section and a horizontal well hole section communicated with the lower end of the vertical well hole section, the directional well pipe is arranged in the directional well hole and comprises a vertical well pipe section and a horizontal well pipe section which are communicated, the vertical well pipe section is located in the vertical well hole section, and the horizontal well pipe section is located in the horizontal well hole section. The high-conductivity cement is filled between the hole wall of the directional well hole and the pipe wall of the directional well pipe, and the freezing point of an injection-production cycle working medium of the underground closed heat removal system is lower than 0 DEG C. According to the invention, the heat obtained by the system in the surrounding rock during each working medium circulation can be relatively increased, that is, the heat extraction capacity of the system is increased, so that the economical efficiency of the system can be improved, and wide application of an underground closed heat extraction technology is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of renewable energy utilization, and in particular to an underground closed heat extraction system, a multi-energy complementary heating system and an operation method thereof. Background Art

[0002] As environmental issues become increasingly prominent, the importance of renewable energy heating has become particularly significant. Geothermal energy is clean and efficient, and is the preferred energy source for renewable energy heating. However, geothermal development usually requires direct extraction of underground hot water or steam, which limits its application in areas with scarce water resources.

[0003] Therefore, in order to avoid resource constraints, related technologies usually use an underground closed heating system to achieve geothermal extraction. This system can extract geothermal heat without extracting groundwater by establishing a closed circulation system. However, due to the low thermal conductivity of underground rocks, the heat extraction per well is relatively low, which affects the economy of the system and is not conducive to the widespread application of underground closed heating technology. Summary of the invention

[0004] The problem solved by the invention is: how to increase the heat intake of an underground closed heat-taking system.

[0005] In order to solve the above problems, the present invention provides an underground closed heat extraction system, a multi-energy complementary heating system and an operation method thereof.

[0006] In the first aspect, the present invention provides an underground closed heat extraction system, comprising a porous rock formation, a directional well pipe and high-conductivity cement, wherein a directional wellbore is drilled in the porous rock formation, the directional wellbore comprises a vertical wellbore section and a horizontal wellbore section connected to the lower end of the vertical wellbore section, the directional well pipe is placed in the directional wellbore, and comprises a vertical well pipe section and a horizontal well pipe section connected to each other, the vertical well pipe section is located in the vertical wellbore section, the horizontal well pipe section is located in the horizontal wellbore section, the high-conductivity cement is filled between the hole wall of the directional wellbore and the pipe wall of the directional well pipe, and the freezing point of the injection and production circulating working fluid of the underground closed heat extraction system is lower than 0°C.

[0007] The beneficial effect of the underground closed heat extraction system of the present invention is: by making the directional wellbore include a vertical wellbore section and a horizontal wellbore section connected to the lower end of the vertical wellbore section to form an L-shaped wellbore, and then by making the directional well pipe include a vertical well pipe section and a horizontal well pipe section connected to each other to form an L-shaped well pipe, in this way, after the vertical well pipe section is placed in the vertical wellbore section and the horizontal well pipe section is placed in the horizontal wellbore section, the lower end of the entire directional well pipe can have a relatively long well pipe section located at the depth of the entire directional wellbore, thereby improving the directional well pipe. The heat exchange area between the lower part of the directional wellbore and the deep part of the porous rock formation can be increased; at the same time, by filling high-conductivity cement between the borehole wall of the directional wellbore and the wall of the directional wellbore, the thermal conductivity of the rock mass around the directional wellbore can be increased; furthermore, by selecting the injection and production circulating working fluid of the underground closed heat extraction system as a working fluid with a freezing point below 0°C, the injection and production circulating working fluid will not freeze even if injected at a temperature below 0°C and can flow and exchange heat in the system, so that the injection temperature of the working fluid can be reduced during the peak period of heating, and the temperature difference between the working fluid and the surrounding rock can be increased. Therefore, the heat exchange area between the lower part of the directional wellbore and the deep part of the porous rock formation can be increased, the thermal conductivity of the rock mass around the directional wellbore can be increased, and the temperature difference between the working fluid and the surrounding rock can be increased, so that the heat obtained by the system in the surrounding rock during each working fluid cycle can be relatively increased, that is, the heat extraction of the system can be increased, and the economic efficiency of the system can be improved, which is conducive to the widespread application of underground closed heat extraction technology.

[0008] Optionally, the injection-production circulating working fluid of the underground closed heat extraction system is ethylene glycol or a salt solution.

[0009] Optionally, the method of filling the high-conductivity cement between the directional wellbore and the directional well pipe is by high-pressure injection.

[0010] Optionally, it also includes an insulation pipe, which is placed in the directional well pipe and includes a vertical insulation pipe section and a horizontal insulation pipe section that are connected. The vertical insulation pipe section is located in the vertical well pipe section, and the horizontal insulation pipe section is located in the horizontal well pipe section.

[0011] Optionally, the directional well pipe also includes a curved well pipe section, the horizontal well pipe section is connected to the vertical well pipe section via the curved well pipe section, and the insulation pipe also includes a curved insulation pipe section, the horizontal insulation pipe section is connected to the vertical insulation pipe section via the curved insulation pipe section.

[0012] In the second aspect, the present invention provides a multi-energy complementary heating system, including a heating building, a heat exchanger, a heat pump unit, an electric heating water tank, a solar collector and the underground closed heating system as described above, the heat exchanger, the heat pump unit and the electric heating water tank are respectively used to heat the heating building, the water outlet of the solar collector is connected to the primary side inlet of the heat exchanger, the water inlet of the solar collector is connected to the primary side outlet of the heat exchanger, the annulus between the directional well pipe and the insulation pipe of the underground closed heating system is connected to the primary side outlet of the heat pump unit, and the insulation pipe is connected to the primary side inlet of the heat pump unit.

[0013] The beneficial effects of the multi-energy complementary heating system of the present invention are: the water outlet of the solar collector, the primary side inlet of the heat exchanger, the primary side outlet of the heat exchanger and the water inlet of the solar collector are connected in sequence to form a circulation loop of solar heating. At the same time, the insulation pipe, the primary side inlet of the heat pump unit, the primary side outlet of the heat pump unit and the annulus are connected in sequence to form a circulation loop of geothermal heating. In addition, the electric heating water tank can realize electric heating. In summary, solar energy, geothermal energy and electric heating water tank can be connected in parallel to provide heating to the heating building, thereby improving the stability of heating. In addition, the electric heating water tank is introduced into the heating system, so that the electrical energy can be converted into thermal energy and stored in the electric heating water tank during the off-peak period, so that electricity can be used during the off-peak period, which is beneficial to improving the economy of the heating system.

[0014] Optionally, the insulation pipe is connected to the primary side inlet of the heat pump unit through a first pipe, and a first valve is provided on the first pipe. The annulus is connected to the primary side outlet of the heat pump unit through a second pipe, and a second valve is provided on the second pipe. The annulus is connected to the water inlet of the solar collector through a third pipe, and a third valve is provided on the third pipe. The insulation pipe is connected to the water outlet of the solar collector through a fourth pipe, and a fourth valve is provided on the fourth pipe. The water inlet of the solar collector is connected to the primary side outlet of the heat exchanger through a fifth pipe, and a fifth valve is provided on the fifth pipe. The water outlet of the solar collector is connected to the primary side inlet of the heat exchanger through a sixth pipe, and a sixth valve is provided on the sixth pipe.

[0015] Optionally, a daily load heat storage tank is further included, the water inlet of the daily load heat storage tank is connected to the water outlet of the solar collector, and the water outlet of the daily load heat storage tank is respectively connected to the fourth pipeline and the sixth pipeline.

[0016] In a third aspect, the present invention provides an operating method of the multi-energy complementary heating system as described above, the operating method comprising:

[0017] In the heating season, the third valve and the fourth valve are closed, and the first valve, the second valve, the fifth valve, the sixth valve and the electric heating water tank are opened, and at the same time, the temperature of the fluid in the annulus between the return directional well pipe and the insulation pipe is adjusted by the heat pump unit;

[0018] In the non-heating season, the third valve and the fourth valve are opened, and the first valve, the second valve, the fifth valve and the sixth valve are closed.

[0019] The beneficial effects of the operating method of the present invention are as follows: by closing the third valve and the fourth valve and opening the first valve, the second valve, the fifth valve, the sixth valve and the electric heating water tank during the heating season, solar energy, geothermal energy and the electric heating water tank can be combined for heating, thereby improving the peak-shaving capacity of the system; at the same time, by adjusting the temperature of the fluid in the annulus between the return directional well pipe and the insulation pipe through the heat pump unit, the injection temperature of the fluid can be changed, for example, the injection temperature is made below 0°C, so as to obtain heat underground that is more suitable for the heating demand, thereby avoiding insufficient geothermal energy or heat waste; in addition, by opening the third valve and the fourth valve and closing the first valve, the second valve, the fifth valve and the sixth valve during the non-heating season, solar energy heating of the surrounding rock can be achieved, thereby preventing the temperature of the rock around the directional well pipe from decaying and improving the stability of the heating power.

[0020] Optionally, the temperature of the fluid in the annulus between the return directional well pipe and the insulation pipe is adjusted by the heat pump unit, including:

[0021] At the beginning and end of heating, the temperature T of the fluid returning to the annulus is adjusted to T≥5°C by the heat pump unit;

[0022] In the middle of heating and when the load is small, the temperature T of the fluid returning to the annulus is adjusted to 0≤T<5°C by the heat pump unit;

[0023] In the middle of heating and when the load is large, the temperature T of the fluid returning to the annulus is adjusted to T<0°C by the heat pump unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of an underground closed heat extraction system according to an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the operation of the multi-energy complementary heating system in the heating season according to an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the operation of the multi-energy complementary heating system in the non-heating season according to an embodiment of the present invention.

[0027] Description of reference numerals:

[0028] 10. Underground closed heating system; 1. Porous rock formation; 11. Directional wellbore; 111. Vertical wellbore section; 112. Horizontal wellbore section; 2. Directional well pipe; 21. Vertical well pipe section; 22. Horizontal well pipe section; 23. Curved well pipe section; 3. High-conductivity cement; 4. Insulated pipe; 41. Vertical insulated pipe section; 42. Horizontal insulated pipe section; 43. Curved insulated pipe section; 5. Annulus; 20. Heating building; 30. Heat exchanger; 40. Heat pump unit; 5 0. Electric heating water tank; 501. Third booster pump; 60. Solar collector; 601. First booster pump; 71. First pipeline; 72. Second pipeline; 721. Second booster pump; 73. Third pipeline; 74. Fourth pipeline; 75. Fifth pipeline; 76. Sixth pipeline; 81. First valve; 82. Second valve; 83. Third valve; 84. Fourth valve; 85. Fifth valve; 86. Sixth valve; 90. Daily load heat storage tank. DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be interpreted as being limited to the embodiments described herein. On the contrary, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0030] The term "including" and its variations used in this document are open inclusions, that is, "including but not limited to"; the term "based on" means "based at least in part on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are only used to distinguish different devices, modules or units, and are not used to limit the order or interdependence of the functions performed by these devices, modules or units.

[0031] It should be noted that the modifications of "one" and "plurality" mentioned in the present invention are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise clearly indicated in the context, it should be understood as "one or more".

[0032] The present invention provides an underground closed heat extraction system, a multi-energy complementary heating system and an operation method thereof, and the present invention can improve the heat extraction of the underground closed heat extraction system.

[0033] like Figure 1 As shown, an underground closed heat extraction system 10 provided by an embodiment of the present invention comprises a porous rock formation 1, a directional well pipe 2 and high-conductivity cement 3, a directional wellbore 11 is drilled in the porous rock formation 1, the directional wellbore 11 comprises a vertical wellbore section 111 and a horizontal wellbore section 112 connected to the lower end of the vertical wellbore section 111, the directional well pipe 2 is placed in the directional wellbore 11, and comprises a vertical well pipe section 21 and a horizontal well pipe section 22 connected to each other, the vertical well pipe section 21 is located in the vertical wellbore section 111, the horizontal well pipe section 22 is located in the horizontal wellbore section 112, the high-conductivity cement 3 is filled between the hole wall of the directional wellbore 11 and the pipe wall of the directional well pipe 2, and the freezing point of the injection and production circulating working fluid of the underground closed heat extraction system 10 is lower than 0°C.

[0034] Among them, the high-conductivity cement 3 is a high-thermal-conductivity cement, for example, it can be a mixture of cement and graphite, it can also be a mixture of cement and metal, it can also be a mixture of cement and high-conductivity siliceous material, and there is no limitation here. In addition, the injection-production circulating working fluid of the underground closed heat extraction system 10 refers to the working fluid that circulates in the system to achieve heat extraction. It should also be noted that the length of the vertical well pipe section 21 can be greater than 2000 meters, and the length of the horizontal well pipe section 22 can be greater than 1000 meters to ensure that the directional well pipe 2 can obtain a sufficiently high temperature underground.

[0035] In this embodiment, the directional wellbore 11 includes a vertical wellbore section 111 and a horizontal wellbore section 112 connected to the lower end of the vertical wellbore section 111 to form an L-shaped wellbore, and the directional well pipe 2 includes a vertical well pipe section 21 and a horizontal well pipe section 22 connected to each other to form an L-shaped well pipe. In this way, after the vertical well pipe section 21 is placed in the vertical wellbore section 111 and the horizontal well pipe section 22 is placed in the horizontal wellbore section 112, a relatively long well pipe section at the lower end of the entire directional well pipe 2 can be located at the depth of the entire directional wellbore 11, thereby improving the The heat exchange area between the lower part of the directional well pipe 2 and the deep part of the porous rock formation 1; at the same time, by filling the high-conductivity cement 3 between the borehole wall of the directional wellbore 11 and the pipe wall of the directional well pipe 2, the thermal conductivity of the rock mass around the directional well pipe 2 can be increased; furthermore, by selecting the injection and production circulating working fluid of the underground closed heat extraction system 10 as a working fluid with a freezing point below 0°C, the injection and production circulating working fluid will not freeze even if injected at a temperature below 0°C and can flow and exchange heat in the system, so that the injection temperature of the working fluid can be reduced during the peak period of heating, and the temperature difference between the working fluid and the surrounding rock can be increased. Therefore, the heat exchange area between the lower part of the directional well pipe 2 and the deep part of the porous rock formation 1 can be increased, the thermal conductivity of the rock mass around the directional well pipe 2 can be increased, and the temperature difference between the working fluid and the surrounding rock can be increased, so that the heat obtained by the system in the surrounding rock during each working fluid cycle can be relatively increased, that is, the heat extraction of the system can be increased, and the economic efficiency of the system can be improved, which is conducive to the widespread application of underground closed heat extraction technology.

[0036] Optionally, the injection-production circulating working fluid of the underground closed heat extraction system 10 is ethylene glycol or a salt solution.

[0037] The salt solution refers to a solution formed by dissolving salts in water, for example, a solution formed by dissolving sodium chloride in water.

[0038] In this optional embodiment, the freezing point of ethylene glycol or salt solution is lower than 0°C, so even if the temperature of the circulating fluid returning to the directional well pipe 2 is lower than 0°C, it will not freeze and can continue to flow to extract heat. This can greatly reduce the temperature of the working fluid flowing back to the directional well pipe 2, thereby increasing the temperature difference between the working fluid and the surrounding rock, greatly increasing the amount of heat extracted.

[0039] Optionally, the high-conductivity cement 3 is filled between the directional wellbore 11 and the directional well pipe 2 by high-pressure injection.

[0040] In this optional embodiment, the high-conductivity cement 3 is injected at high pressure. Since the directional wellbore 11 is surrounded by porous rocks with rich pore structures, the high-conductivity cement 3 will also be filled into the surrounding porous rocks, thereby improving the thermal conductivity of the surrounding rocks.

[0041] Alternatively, if Figure 1As shown, the underground closed heat extraction system 10 also includes an insulation pipe 4, which is placed in the directional well pipe 2 and includes a vertical insulation pipe section 41 and a horizontal insulation pipe section 42 that are connected. The vertical insulation pipe section 41 is located in the vertical well pipe section 21, and the horizontal insulation pipe section 42 is located in the horizontal well pipe section 22.

[0042] Specifically, the thermal insulation pipe 4 may adopt a vacuum thermal insulation structure to achieve thermal insulation. It can be understood that after the insulation pipe 4 is placed in the directional well pipe 2, an annulus 5 (i.e., annular space) can be formed between the insulation pipe 4 and the directional well pipe 2, so that the working fluid can flow through the annulus 5 and the insulation pipe 4 in sequence. When underground heat extraction is required, the cold fluid can be injected into the annulus 5 between the directional well pipe 2 and the insulation pipe 4, gradually downward along the annulus 5 to obtain the heat of the surrounding rock to become a hot fluid, and then the hot fluid enters the insulation pipe 4 from the end of the horizontal insulation pipe section 42 away from the vertical insulation pipe section 41, gradually upward along the insulation pipe 4 and finally leaves the insulation pipe 4 to achieve underground heat extraction. When it is necessary to supplement the heat of the surrounding rock, the hot fluid can be injected into the insulation pipe 4, gradually downward along the insulation pipe 4, and then enter the annulus 5 between the directional well pipe 2 and the insulation pipe 4 from the end of the horizontal insulation pipe section 42 away from the vertical insulation pipe section 41, gradually upward along the annulus 5 to dissipate the heat into the surrounding rock to become a cold fluid and finally leave the annulus 5, finally achieving heat supplement for the surrounding rock.

[0043] In this optional embodiment, the insulation pipe 4 includes a connected vertical insulation pipe section 41 and a horizontal insulation pipe section 42, so that the overall shape of the insulation pipe 4 is L-shaped, thereby achieving shape adaptation between the insulation pipe 4 and the directional well pipe 2, which is beneficial to ensure smooth flow of the fluid.

[0044] Alternatively, if Figure 1 As shown, the directional well pipe 2 also includes a curved well pipe section 23, and the horizontal well pipe section 22 is connected to the vertical well pipe section 21 through the curved well pipe section 23. The insulation pipe 4 also includes a curved insulation pipe section 43, and the horizontal insulation pipe section 42 is connected to the vertical insulation pipe section 41 through the curved insulation pipe section 43.

[0045] It should be noted that a sealing plate may be provided at one end of the horizontal well pipe section 22 away from the curved well pipe section 23 to seal the end of the horizontal well pipe section 22 and prevent the working fluid from leaking from the end into the surrounding porous rock.

[0046] In this optional embodiment, the connection between the horizontal well pipe section 22 and the vertical well pipe section 21 is achieved by bending the well pipe section 23, and the connection between the horizontal insulation pipe section 42 and the vertical insulation pipe section 41 is achieved by bending the insulation pipe section 43. In this way, the curved well pipe section 23 and the curved insulation pipe section 43 can smoothly change the flow direction of the fluid, reduce the pressure loss of the fluid during turning, and ensure that the fluid can flow more smoothly.

[0047] like Figure 2 and Figure 3 As shown, a multi-energy complementary heating system provided by an embodiment of the present invention includes a heating building 20, a heat exchanger 30, a heat pump unit 40, an electric heating water tank 50, a solar collector 60 and the underground closed heating system 10 as described above, wherein the heat exchanger 30, the heat pump unit 40 and the electric heating water tank 50 are respectively used to heat the heating building 20, the water outlet of the solar collector 60 is connected to the primary side inlet of the heat exchanger 30, the water inlet of the solar collector 60 is connected to the primary side outlet of the heat exchanger 30, the annulus 5 between the directional well pipe 2 and the insulation pipe 4 of the underground closed heating system 10 is connected to the primary side outlet of the heat pump unit 40, and the insulation pipe 4 is connected to the primary side inlet of the heat pump unit 40.

[0048] It should be noted that both the heat exchanger 30 and the heat pump unit 40 may have a primary side and a secondary side that can exchange heat with each other. The primary side is the side connected to the heat source, which often includes an inlet and an outlet. Correspondingly, the secondary side is the side connected to the user end, which often includes an inlet and an outlet. In addition, for the heat exchanger 30, the inlet and outlet of its secondary side can be connected to the heating equipment of the heating building 20 respectively to achieve heating for the heating building 20. For the heat pump unit 40, the inlet and outlet of its secondary side can also be connected to the heating equipment of the heating building 20 respectively to achieve heating for the heating building 20. In addition, the inlet and outlet of the electric heating water tank 50 can also be connected to the heating equipment of the heating building 20 respectively to achieve heating for the heating building 20.

[0049] In this embodiment, the water outlet of the solar collector 60, the primary side inlet of the heat exchanger 30, the primary side outlet of the heat exchanger 30 and the water inlet of the solar collector 60 are connected in sequence to form a circulation loop of solar heating. At the same time, the insulation pipe 4, the primary side inlet of the heat pump unit 40, the primary side outlet of the heat pump unit 40 and the annulus 5 are connected in sequence to form a circulation loop of geothermal heating. In addition, the electric heating water tank 50 can realize electric heating. In summary, solar energy, geothermal energy and the electric heating water tank 50 can be connected in parallel to heat the heating building 20, thereby improving the stability of heating. In addition, the electric heating water tank 50 is introduced into the heating system, so that the electrical energy can be converted into thermal energy and stored in the electric heating water tank 50 during the off-peak period, so that electricity can be used during the off-peak period, which is conducive to improving the economy of the heating system.

[0050] Alternatively, if Figure 2 and Figure 3As shown, the insulation pipe 4 is connected to the primary side inlet of the heat pump unit 40 through the first pipe 71, and the first pipe 71 is provided with a first valve 81. The annulus 5 is connected to the primary side outlet of the heat pump unit 40 through the second pipe 72, and the second pipe 72 is provided with a second valve 82. The annulus 5 is connected to the water inlet of the solar collector 60 through the third pipe 73, and the third pipe 73 is provided with a third valve 83. The insulation pipe 4 is connected to the water outlet of the solar collector 60 through the fourth pipe 74, and the fourth pipe 74 is provided with a fourth valve 84. The water inlet of the solar collector 60 is connected to the primary side outlet of the heat exchanger 30 through the fifth pipe 75, and the fifth pipe 75 is provided with a fifth valve 85. The water outlet of the solar collector 60 is connected to the primary side inlet of the heat exchanger 30 through the sixth pipe 76, and the sixth pipe 76 is provided with a sixth valve 86.

[0051] Specifically, a first booster pump 601 can be provided between the connection point of the fourth pipeline 74 and the sixth pipeline 76 and the water outlet of the solar collector 60, so that the first booster pump 601 can be used to adjust the pressure of the fluid to ensure that the fluid circulates effectively in the circulation loop of solar energy. In addition, a second booster pump 721 can be provided on the second pipeline 72, so that the second booster pump 721 can be used to adjust the pressure of the fluid to ensure that the fluid circulates effectively in the circulation loop of geothermal energy. In addition, a third booster pump 501 can be provided on the pipeline between the electric heating water tank 50 and the heating building 20, so that the third booster pump 501 can be used to adjust the pressure of the fluid to ensure that the fluid circulates effectively between the electric heating water tank 50 and the heating building 20.

[0052] In this optional embodiment, it can be understood that as the amount of heat taken by the underground closed heat extraction system 10 increases, the temperature of the rocks around the directional well pipe 2 will drop more significantly, which may easily cause a decrease in the continuous heat extraction performance and affect the stability and sustainability of the system. Therefore, in this solution, a third pipe 73 is connected between the annulus 5 and the water inlet of the solar collector 60, and a fourth pipe 74 is connected between the insulation pipe 4 and the water outlet of the solar collector 60, so that the solar collector 60 can be connected to the underground closed heat extraction system 10, so that when the first valve 81 on the first pipe 71 and the second valve 82 on the second pipe 72 are closed, the solar collector 60 can be connected to the underground closed heat extraction system 10. When valve 82, the fifth valve 85 on the fifth pipeline 75 and the sixth valve 86 on the sixth pipeline 76, and the third valve 83 on the third pipeline 73 and the fourth valve 84 on the fourth pipeline 74 are opened, the hot fluid heated in the solar collector 60 can enter the insulation pipe 4 through the fourth pipeline 74 and then enter the annulus 5, and then gradually move upward along the annulus 5 to dissipate the heat to the surrounding rock and then become a cold fluid, and then the cold fluid returns to the solar collector 60 through the third pipeline 73 to continue heating, and finally realizes solar heating of the surrounding rock, thereby preventing the temperature of the rock around the directional well pipe 2 from decaying and improving the stability of the heat extraction power.

[0053] Alternatively, if Figure 2 and Figure 3 As shown, the multi-energy complementary heating system also includes a daily load heat storage tank 90, the water inlet of the daily load heat storage tank 90 is connected to the water outlet of the solar collector 60, and the water outlet of the daily load heat storage tank 90 is respectively connected to the fourth pipeline 74 and the sixth pipeline 76.

[0054] In this optional embodiment, the daily load heat storage tank 90 is a device for storing thermal energy collected and converted by the solar collector 60. It stores excess heat when solar energy is sufficient and releases the heat during periods of insufficient solar energy or at night, thereby effectively solving the problem of unstable solar energy supply.

[0055] An embodiment of the present invention provides an operating method of the multi-energy complementary heating system as described above, the operating method comprising:

[0056] Step S1: In the heating season, close the third valve 83 and the fourth valve 84, and open the first valve 81, the second valve 82, the fifth valve 85, the sixth valve 86 and the electric heating water tank 50, and at the same time adjust the fluid temperature of the annulus 5 between the return directional well pipe 2 and the insulation pipe 4 through the heat pump unit 40.

[0057] Step S2: In the non-heating season, the third valve 83 and the fourth valve 84 are opened, and the first valve 81 , the second valve 82 , the fifth valve 85 and the sixth valve 86 are closed.

[0058] Specifically, step S1 can refer to Figure 2 , step S2 can refer to Figure 3 .

[0059] It should be noted that the heating season is the season when the temperature drops and heating equipment is needed to maintain indoor warmth, and the non-heating season is the other season of the year except the heating season.

[0060] It can be understood that in step S1, if Figure 2 As shown, when the third valve 83 and the fourth valve 84 are closed and the first valve 81 and the second valve 82 are opened, the fluid in the underground closed heat extraction system 10 will not flow to the solar collector 60 but will only flow to the heat pump unit 40. Specifically, see Figure 2 In the flow direction indicated by the middle arrow, the hot fluid in the insulation pipe 4 will enter the heat pump unit 40 through the first pipe 71, exchange heat in the heat pump unit 40 to become a cold fluid, and then return to the annulus 5 between the directional well pipe 2 and the insulation pipe 4 through the second pipe 72 to continue to extract heat, thereby realizing geothermal heating; when the fifth valve 85 and the sixth valve 86 are opened, the hot fluid in the daily load heat storage tank 90 will enter the heat exchanger 30 through the sixth pipe 76, exchange heat in the heat exchanger 30 to become a cold fluid, and then return to the solar collector 60 through the fifth pipe 75 to continue heating, thereby realizing solar heating; when the electric heating water tank 50 is opened, the electric heating water tank 50 can transport hot water to the heating building 20, thereby realizing heating by the electric heating water tank 50.

[0061] It can also be understood that in step S2, if Figure 3 As shown, when the third valve 83 and the fourth valve 84 are opened and the first valve 81, the second valve 82, the fifth valve 85 and the sixth valve 86 are closed, the fluid in the underground closed heat extraction system 10 will not flow to the heat pump unit 40 but will only flow to the solar collector 60. Specifically, see Figure 3 In the flow direction indicated by the middle arrow, the cold fluid in the annulus 5 will enter the solar collector 60 through the third pipeline 73, be heated in the solar collector 60 to become a hot fluid, and then return to the insulation pipe 4 through the daily load heat storage tank 90 and the fourth pipeline 74 in sequence, and then flow along the annulus 5 to dissipate heat into the porous rock layer 1, thereby realizing solar heating of the surrounding rock.

[0062] In this embodiment, by closing the third valve 83 and the fourth valve 84 and opening the first valve 81, the second valve 82, the fifth valve 85, the sixth valve 86 and the electric heating water tank 50 during the heating season, solar energy, geothermal energy and the electric heating water tank 50 can be combined for heating, thereby improving the peak-shaving capacity of the system. At the same time, the temperature of the fluid in the annulus 5 between the return directional well pipe 2 and the insulation pipe 4 is adjusted by the heat pump unit 40, and the injection temperature of the fluid can be changed, for example, the injection temperature is made below 0°C, so as to obtain heat that is more suitable for the heating demand underground, thereby avoiding insufficient geothermal energy or heat waste. In addition, by opening the third valve 83 and the fourth valve 84 and closing the first valve 81, the second valve 82, the fifth valve 85 and the sixth valve 86 during the non-heating season, solar energy heating of the surrounding rock can be achieved, thereby preventing the temperature of the rock around the directional well pipe 2 from decaying and improving the stability of the heating power.

[0063] It should be noted that the water temperature of the heat pump unit 40 for heating the heating building 20 can be 45°C, and the water temperature of the return water from the heating building 20 to the heat pump unit 40 can be 36°C, so as to ensure that the heating temperature is appropriate. In addition, in the heating season, the fluid temperatures entering and leaving the solar collector 60 can be 40°C and 50°C, respectively. At the same time, in the non-heating season, the temperature of the fluid flowing out of the solar collector 60 must be higher than the temperature of the rocks around the directional well pipe 2, so as to ensure the heating effect on the rocks around the directional well pipe 2.

[0064] Optionally, the temperature of the fluid in the annulus 5 between the return directional well pipe 2 and the insulation pipe 4 is adjusted by the heat pump unit 40, including:

[0065] Step S11: At the beginning and the end of heating, the temperature T of the fluid returning to the annulus 5 is adjusted to T≥5°C by the heat pump unit 40.

[0066] Step S12: In the middle of heating and when the load is relatively small, the temperature T of the fluid returning to the annulus 5 is adjusted to 0≤T<5°C by the heat pump unit 40.

[0067] Step S13: When the heating is in the middle stage and the load is large, the temperature T of the fluid returning to the annulus 5 is adjusted to T<0°C by the heat pump unit 40.

[0068] In this optional embodiment, since the heat load is small at the beginning and end of heating, the required heat is small, and step S11 can relatively reduce the heat intake in the underground surrounding rock by adjusting T to T≥5°C, so that the heat intake is adapted to the heat demand at the beginning and end of heating; when the heating is in the middle stage and the load is small, the heat load increases compared with the beginning and end of heating, and the required heat increases, and step S12 can further increase the heat intake in the underground surrounding rock by adjusting T to 0≤T<5°C, so that the heat intake is adapted to the heat demand when the load is small in the middle stage of heating; when the heating is in the middle stage and the load is large, the heat load is large and the required heat is more, and step S13 can increase the heat intake in the underground surrounding rock to a greater extent for peak regulation by adjusting T to T<0°C, so that the heat intake is adapted to the heat demand when the load is large in the middle stage of heating. In summary, the mutual adaptation between geothermal heat intake and heat load in different periods of the heating season is achieved, which can avoid insufficient geothermal heat or heat waste.

[0069] Although the present invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

Claims

1. An underground closed heat extraction system, characterized in that: The invention comprises a porous rock formation (1), a directional wellbore (11) drilled in the porous rock formation (1), the directional wellbore (11) comprising a vertical wellbore section (111) and a horizontal wellbore section (112) connected to the lower end of the vertical wellbore section (111), the directional wellbore (2) being placed in the directional wellbore (11) and comprising a vertical wellbore section (21) and a horizontal wellbore section (22) connected to each other, the vertical wellbore section (21) being located in the vertical wellbore section (111), the horizontal wellbore section (22) being located in the horizontal wellbore section (112), the high-conductivity cement (3) being filled between the hole wall of the directional wellbore (11) and the pipe wall of the directional wellbore (2), and the freezing point of the injection and production circulating working fluid of the underground closed heat extraction system (10) being lower than 0°C.

2. The underground closed heat extraction system according to claim 1, characterized in that: The injection-production circulating working fluid of the underground closed heat extraction system (10) is ethylene glycol or a salt solution.

3. The underground closed heat extraction system according to claim 1, characterized in that: The method for filling the high-conductivity cement (3) between the directional wellbore (11) and the directional well pipe (2) is high-pressure injection.

4. The underground closed heat extraction system according to claim 1, characterized in that: It also includes an insulation pipe (4), which is placed in the directional well pipe (2) and includes a vertical insulation pipe section (41) and a horizontal insulation pipe section (42) that are connected to each other. The vertical insulation pipe section (41) is located in the vertical well pipe section (21), and the horizontal insulation pipe section (42) is located in the horizontal well pipe section (22).

5. The underground closed heat extraction system according to claim 4, characterized in that: The directional well pipe (2) further comprises a curved well pipe section (23), and the horizontal well pipe section (22) is connected to the vertical well pipe section (21) via the curved well pipe section (23). The insulation pipe (4) further comprises a curved insulation pipe section (43), and the horizontal insulation pipe section (42) is connected to the vertical insulation pipe section (41) via the curved insulation pipe section (43).

6. A multi-energy complementary heating system, characterized in that: The invention comprises a heating building (20), a heat exchanger (30), a heat pump unit (40), an electric heating water tank (50), a solar thermal collector (60) and an underground closed heat extraction system (10) as claimed in any one of claims 1 to 5, wherein the heat exchanger (30), the heat pump unit (40) and the electric heating water tank (50) are respectively used to provide heating to the heating building (20), the water outlet of the solar thermal collector (60) is connected to the primary side inlet of the heat exchanger (30), the water inlet of the solar thermal collector (60) is connected to the primary side outlet of the heat exchanger (30), the annulus (5) between the directional well pipe (2) and the insulation pipe (4) of the underground closed heat extraction system (10) is connected to the primary side outlet of the heat pump unit (40), and the insulation pipe (4) is connected to the primary side inlet of the heat pump unit (40).

7. The multi-energy complementary heating system according to claim 6, characterized in that: The insulation pipe (4) is connected to the primary side inlet of the heat pump unit (40) through a first pipe (71), and the first pipe (71) is provided with a first valve (81). The annulus (5) is connected to the primary side outlet of the heat pump unit (40) through a second pipe (72), and the second pipe (72) is provided with a second valve (82). The annulus (5) is connected to the water inlet of the solar collector (60) through a third pipe (73), and the third pipe (73) is provided with a third valve (83). The insulation pipe (4) The solar thermal collector (60) is connected to the water outlet via a fourth pipe (74), and a fourth valve (84) is provided on the fourth pipe (74). The water inlet of the solar thermal collector (60) is connected to the primary side outlet of the heat exchanger (30) via a fifth pipe (75), and a fifth valve (85) is provided on the fifth pipe (75). The water outlet of the solar thermal collector (60) is connected to the primary side inlet of the heat exchanger (30) via a sixth pipe (76), and a sixth valve (86) is provided on the sixth pipe (76).

8. The multi-energy complementary heating system according to claim 7, characterized in that: It also comprises a daily load heat storage tank (90), the water inlet of the daily load heat storage tank (90) being connected to the water outlet of the solar thermal collector (60), and the water outlet of the daily load heat storage tank (90) being connected to the fourth pipeline (74) and the sixth pipeline (76) respectively.

9. An operating method of a multi-energy complementary heating system according to any one of claims 6 to 8, characterized in that: The operation method comprises: In the heating season, the third valve (83) and the fourth valve (84) are closed, and the first valve (81), the second valve (82), the fifth valve (85), the sixth valve (86) and the electric heating water tank (50) are opened, and at the same time, the temperature of the fluid in the annulus (5) between the return directional well pipe (2) and the insulation pipe (4) is adjusted through the heat pump unit (40); In the non-heating season, the third valve (83) and the fourth valve (84) are opened, and the first valve (81), the second valve (82), the fifth valve (85) and the sixth valve (86) are closed.

10. The operating method of the multi-energy complementary heating system according to claim 9, characterized in that: The method of adjusting the temperature of the fluid in the annulus (5) between the return directional well pipe (2) and the insulation pipe (4) by means of the heat pump unit (40) comprises: At the beginning and end of heating, the temperature T of the fluid returning to the annulus (5) is adjusted to T≥5°C by the heat pump unit (40); In the middle of heating and when the load is relatively small, the temperature T of the fluid returning to the annulus (5) is adjusted to 0≤T<5°C by the heat pump unit (40); In the middle of heating and when the load is large, the temperature T of the fluid returning to the annulus (5) is adjusted to T<0°C by the heat pump unit (40).

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