A method for geothermal extraction power generation and combined heat and power (CHP) in coal mines based on sCO2 cycle

Abstract

This invention discloses a method for power generation and combined heat, power and cooling (CHP) of geothermal extraction in coal mines based on sCO2 circulation, comprising: determining the underground surrounding rock heat extraction zone and geothermal well; designing circulation pipelines and surface equipment parameters; burying heat exchange pipelines in the mine wall to form a cooling loop; installing heat exchangers in the geothermal well to establish a closed-loop water-steam circulation; laying insulated pipelines along the vertical shaft and roadways, connecting the underground heat exchangers with surface coupling units, ORC units, and heat exchange units to form a closed loop; installing a coupling system and sensors on the surface, including compressors, overflow valves, auxiliary pumps, throttle valve groups, and heat exchange units; injecting sCO2 into the loop, utilizing the temperature difference between the underground heat source and the surface cold source to form a thermosiphon self-circulation; adjusting the working fluid pressure, flow rate, and temperature through the coupling units, while simultaneously extracting low-grade heat from the surrounding rock and heat from the geothermal well; using high-temperature sCO2 on the surface to drive ORC power generation, with waste heat used for heating, and low-temperature working fluid returned to the underground to cool the roadway air, thus achieving combined power generation, heating, and cooling.

Description

Technical Field

[0001] This invention relates to the field of green transformation of mines and geothermal resource development technology, and in particular to a method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle. Background Technology

[0002] As shallow coal resources are gradually depleted, the depth of coal mining in my country is increasing at a rate of 10-20 meters per year. Currently, there are over 100 mines with depths exceeding 800 meters, and some mines even exceed 1500 meters. This increase in mining depth has brought about a serious problem—high-temperature heat hazards in the mines.

[0003] To address the heat hazards in mines, scholars and engineers both domestically and internationally have conducted extensive research. Existing technologies can be broadly categorized as follows: Ventilation cooling method: This method removes heat by increasing airflow. It is effective in shallow wells, but for deep wells, limited by the cross-section of the shaft and the capacity of the fan, simply increasing the airflow is insufficient to effectively reduce the working face temperature, and energy consumption increases dramatically. Ground-based centralized cooling system: This system produces chilled water or ice slurry on the ground and transports it through pipelines to an underground air cooler for cooling. However, this system has drawbacks such as requiring a high-power circulating pump for long-distance chilled water transport, resulting in high energy consumption; low heat dissipation efficiency of the ground condenser in high summer temperatures, leading to a decrease in the system's energy efficiency ratio; and the heat extracted from the well is ultimately discharged into the atmosphere through a cooling tower, resulting in waste heat. Underground centralized cooling system: This system places the refrigeration unit underground, reducing transport distance. However, underground spaces are narrow and ventilation is poor, making heat dissipation difficult for the unit, and it must meet explosion-proof requirements, resulting in high equipment investment and maintenance costs.

[0004] The aforementioned research indicates that mine surrounding rock and deep geothermal energy have considerable utilization value. While existing research has proposed a few multifunctional integrated system solutions, these solutions mostly remain at the theoretical simulation or patent stage, and have not yet achieved engineering verification and comprehensive application. Breakthroughs are particularly needed in the synergistic optimization of energy cascade utilization and pump-free self-driven circulation. Furthermore, existing cooling systems directly discharge the extracted 40-50℃ waste heat, wasting energy and causing thermal pollution; while independent geothermal power generation systems require dedicated wells and are not integrated with existing mine roadways, ventilation, drainage, and other infrastructure, resulting in high investment costs. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, the first objective of this invention is to propose a method for coal mine geothermal extraction power generation and combined heat, power, and cooling based on supercritical carbon dioxide (sCO2) circulation. This method utilizes underground surrounding rock heat extraction pipelines and deep geothermal well water-vapor circulation systems to collect low-grade and medium-to-high-temperature geothermal resources through a supercritical carbon dioxide (sCO2) main closed-loop circuit. This fuels surface ORC generators to produce green electricity, and the waste heat from power generation is used for district heating. Simultaneously, the recycled low-temperature sCO2 is used for air cooling in mine roadways, achieving integrated power generation, heating, and cooling.

[0006] To achieve the above objectives, a first aspect of the present invention proposes a method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle, comprising the following steps: S1, determine the heat extraction zone of the surrounding rock in the well and the geothermal well, and design the parameters of the circulation pipeline, surface coupling unit, ORC generator set and heating network; S2, heat exchange pipes are buried in the mine wall to form a cooling loop, and heat exchangers are installed in the geothermal well to establish a closed water-vapor circulation. S3, with insulated pipelines laid along the shaft and tunnel, the lower end of the shaft is connected to the heat exchange pipeline and geothermal heat exchanger, and the surface end is connected to the coupling unit, ORC generator set and heat exchange unit to form a closed loop. S4, a coupling system including a compressor, overflow valve, auxiliary pump, throttling valve group and heat exchanger unit is installed on the ground, connected to a closed loop, and sensors and flow valves are installed in the pipeline; S5, supercritical carbon dioxide working fluid is injected into the loop to form a thermosiphon self-circulation by utilizing the temperature difference between the downhole heat source and the surface cold source; S6 regulates the pressure, flow rate, and temperature of supercritical carbon dioxide through the coupling unit: starting the auxiliary pump or compressor to compensate for the pressure head, adjusting the throttle valve and overflow valve to control the flow rate and pressure, and adjusting the heat exchange unit to control the cooling temperature; at the same time, it extracts low-grade heat from the surrounding rock through the mine wall circuit and transfers the heat to the working fluid through the geothermal well water vapor circulation. S7 is an ORC generator set driven by supercritical carbon dioxide at high surface temperature. The waste heat from power generation is used for heating, and the low-temperature working fluid after heat release is returned to the underground cooling tunnel air, realizing the combined production of power generation, heating and cooling.

[0007] In addition, the coal mine geothermal extraction power generation and cogeneration method based on sCO2 cycle according to the above embodiments of the present invention may also have the following additional technical features: According to an embodiment of the present invention, in step S2, the heat exchange pipes in the mine wall are covered with a heat-conducting layer made of polymer or metal materials, and their burial depth and spacing are determined by optimization based on the thermal properties of the surrounding rock; the water vapor circulation system in the deep geothermal well is a closed loop, and the working fluid is treated mine water or pure water.

[0008] According to an embodiment of the present invention, in step S3, when the supercritical carbon dioxide heat-insulated circulation pipeline is laid along the vertical shaft, a double-layer heat-insulating structure is adopted. The inner layer is a pressure-resistant metal corrugated pipe, and the outer layer is a low thermal conductivity heat-insulating material and a waterproof protective layer, and fixed supports are provided at intervals.

[0009] According to an embodiment of the present invention, in step S4, the surface multi-functional coupling unit integrates an intelligent control module. The intelligent control module is connected to a temperature sensor, a pressure sensor, and a flow control valve signal, and is used to automatically adjust the compressor start / stop, auxiliary pump speed, and valve opening according to real-time operating conditions.

[0010] According to one embodiment of the present invention, in step S5, when the temperature difference between the downhole heat source and the surface cold source is insufficient to establish a stable thermosiphon cycle, an initial cycle driving force is provided by an auxiliary pump or compressor, and the system automatically switches to self-circulation mode after the temperature difference is restored.

[0011] According to one embodiment of the present invention, in step S6, the cooling medium of the surface heat exchanger unit is mine water, return airflow, surface pond water, or winter ambient air.

[0012] According to an embodiment of the present invention, in step S7, the evaporator of the ORC generator set exchanges heat with the supercritical carbon dioxide loop, and the condenser is connected to the surface cooling system; the waste heat of the supercritical carbon dioxide after power generation is first used for heating by the heat exchange unit. When the heating load is lower than the threshold, the excess heat is discharged to the environment through the auxiliary heat dissipation device; the low-temperature supercritical carbon dioxide returning to the well preferentially passes through the roadway air cooler to cool the working face air. When the return liquid temperature is higher than the set threshold, the bypass part of the flow is directly returned to the heat source area.

[0013] According to one embodiment of the present invention, a safety interlock protection step is also included: when a supercritical carbon dioxide leak is detected or the pipeline pressure exceeds the design range, the main valve of the surface multi-functional coupling unit is automatically closed and the downhole ventilation enhancement program is started.

[0014] According to one embodiment of the present invention, in step S6, the cooling temperature of supercritical carbon dioxide is precisely controlled by adjusting the surface heat exchange unit to regulate the circulation driving force; when the working conditions of the underground heat source or the surface cold source change, the system adapts to the variable load condition through the dynamic adjustment of the surface multi-functional coupling unit.

[0015] According to one embodiment of the present invention, after step S7, when the return liquid temperature of the low-temperature supercritical carbon dioxide returned to the well is lower than a set threshold, the corresponding branch valve is closed, and the circulation is transferred to the next mining area or put into maintenance mode; thus realizing the collaborative operation mode of "extracting heat first and then mining coal".

[0016] Compared with existing technologies, the advantages of the coal mine geothermal extraction power generation and cogeneration method based on sCO2 cycle disclosed in this invention are as follows: (1) Multifunctional integration: The four functions of low-grade heat recovery from surrounding rock of mine, deep geothermal power generation, district heating and mine cooling are integrated into the same sCO2 closed-loop system, realizing the fundamental transformation from heat hazard control to clean energy production.

[0017] (2) Low energy consumption and long distance transmission: The temperature difference between the downhole heat source and the surface cold source is used to drive the thermosiphon self-circulation, which significantly reduces pumping energy consumption compared with traditional water circulation and overcomes the pressure drop problem of ultra-long distance fluid transportation in deep wells.

[0018] (3) High-efficiency energy utilization in cascade: high-temperature sCO2 is used for ORC power generation, medium-temperature waste heat after power generation is used for heating, and low-temperature sCO2 is used for mine cooling, realizing temperature matching and cascade utilization of thermal energy, and the system has high comprehensive energy efficiency.

[0019] (4) Safety and environmental protection: CO2 is non-toxic, non-flammable, and chemically inert. After leakage, it can be quickly diluted and discharged through the existing ventilation system of the mine. The system has no high-pressure flammable working fluid, has excellent explosion-proof performance, and is suitable for underground coal mine environments.

[0020] (5) Economy and scalability: Make full use of existing mine roadways, shafts, ventilation and other infrastructure, without the need to drill geothermal wells separately (deep geothermal wells can be combined with mine drainage or exploration boreholes), and the investment cost is controllable; the system can be modularly deployed and the power generation or heating capacity can be flexibly configured according to the geothermal resource conditions of the mining area.

[0021] (6) Promote the green transformation of mines: Transform traditional coal mines from energy-consuming centers into clean energy production bases that integrate power generation, heating and cooling, reduce external electricity purchase and heating costs, and reduce carbon emissions.

[0022] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the rock wall thermal energy extraction pipeline network layout according to an embodiment of the present invention; Figure 3 This is a schematic diagram of a surface-mounted generator unit according to an embodiment of the present invention; Figure 4 This is a schematic diagram of an underground unit according to an embodiment of the present invention. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0025] The following description, with reference to the accompanying drawings, describes a method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle, according to an embodiment of the present invention.

[0026] like Figure 1 As shown, the method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to an embodiment of the present invention includes the following steps: S1, determine the heat extraction zone of the surrounding rock in the well and the geothermal well, and design the parameters of the circulation pipeline, surface coupling unit, ORC generator set and heating network.

[0027] Specifically, the process begins with geological exploration and thermal resource assessment. Through geological surveys, geothermal gradient measurements, and thermal property tests, data on the thermal conductivity, specific heat capacity, density, and geothermal gradient of the deep coal mine surrounding rock are obtained to determine the boundary, thickness, and thermal reservoir potential of the underground surrounding rock heat extraction area. Next, drilling locations are determined. Specifically, based on the geological structure and existing mine layout, the location, number, depth, and well structure of deep geothermal wells are determined, prioritizing the use of existing exploration boreholes, drainage holes, or dedicated geothermal wells. Pipeline system design can be based on mine depth (e.g., 600-1500 meters), heat source temperature (surrounding rock 40-50℃, geothermal wells can reach 80-120℃), and surface cold source conditions (ambient temperature, cooling water temperature). This involves designing the diameter, wall thickness, insulation layer thickness, and material of the sCO2 circulation trunk pipeline, and calculating the thermosiphon head and circulation flow rate. The selection of surface equipment specifically includes: designing the specifications of the surface multi-functional coupling unit (compressor, overflow valve, auxiliary pump, throttling speed control valve group, heat exchanger unit); determining the evaporation temperature, condensation temperature, and rated power of the ORC generator set; and designing the parameters of the heat exchanger unit and heating network according to the regional heating load.

[0028] S2, heat exchange pipes are buried in the mine wall to form a cooling loop, and heat exchangers are installed in the geothermal well to establish a closed water-vapor circulation.

[0029] According to an embodiment of the present invention, in step S2, the heat exchange pipes in the mine wall are covered with a heat-conducting layer made of polymer or metal materials, and their burial depth and spacing are determined by optimization based on the thermal properties of the surrounding rock; the water vapor circulation system in the deep geothermal well is a closed loop, and the working fluid is treated mine water or pure water.

[0030] Specifically, when laying heat exchange pipes in the mine wall, directional boreholes are drilled along the sidewalls or roof of the mine roadway at designed intervals (e.g., 1.5~3.0 meters) into the surrounding rock. The borehole depth is determined based on the heat-affected radius (e.g., 10~30 meters). Heat exchange pipes are laid in each borehole, and the pipes are covered with a heat-conducting layer made of polymer materials (e.g., polyethylene) or metal materials (e.g., stainless steel) to form a primary mine cooling circuit.

[0031] During pipe connection and sealing, heat exchange pipes in adjacent boreholes are connected in series or parallel, with joints using heat fusion, threaded, or quick-connect sealing structures to ensure long-term pressure and corrosion resistance. Water collection mains and valves are installed at the inlet and outlet of the circuit.

[0032] When installing heat exchangers in deep geothermal wells, U-tube or coaxial sleeve heat exchangers are lowered into the geothermal wells (800-2000 meters deep) drilled in the mining area. The heat exchangers are made of high-temperature resistant stainless steel or special alloys. A closed underground water-vapor circulation system is established, using deoxygenated and softened mine water or pure water as the circulating working fluid to prevent scaling and corrosion.

[0033] Finally, a circulation pump, expansion tank, pressure gauge, and temperature sensor are installed at the geothermal wellhead to form an independent closed-loop water vapor circulation circuit for extracting heat from the high-temperature rock strata at the bottom of the well (e.g., 100~150℃).

[0034] S3, with insulated pipelines laid along the shaft and tunnel, the lower end of the shaft is connected to the heat exchange pipeline and geothermal heat exchanger, and the surface end is connected to the coupling unit, ORC generator set and heat exchange unit to form a closed loop.

[0035] According to an embodiment of the present invention, in step S3, when the supercritical carbon dioxide heat-insulated circulation pipeline is laid along the vertical shaft, a double-layer heat-insulating structure is adopted. The inner layer is a pressure-resistant metal corrugated pipe, and the outer layer is a low thermal conductivity heat-insulating material and a waterproof protective layer, and fixed supports are provided at intervals.

[0036] Specifically, pipeline laying route planning: the route of the sCO2 insulation circulation pipeline is planned along the mine shaft and the main underground roadways to avoid interference with ventilation, drainage, power supply and other facilities, and maintenance passages and safety distances are set up.

[0037] Vertical shaft pipeline installation: The sCO2 main pipeline is laid inside the vertical shaft. The pipeline adopts a double-layer insulation structure—the inner layer is a pressure-resistant metal corrugated pipe (material: 316L stainless steel, pressure resistance ≥15MPa), and the outer layer is covered with a low thermal conductivity insulation material (such as aerogel felt or polyurethane foam) and a waterproof protective layer (such as PVC or galvanized iron sheet). Fixed supports and guide supports are installed along the shaft at appropriate intervals (such as 5~10 meters) to prevent excessive stress on the pipeline due to its own weight and thermal expansion and contraction.

[0038] Pipeline laying in the tunnel section: sCO2 pipelines are suspended or supported on the sidewalls or roof of the underground tunnels. The pipelines also adopt a heat-insulating structure, with drain valves at low points and air vent valves at high points. The underground end of the pipeline is connected to the outlet of the mine wall heat exchange pipeline and the outlet of the heat exchanger in the geothermal well via a manifold; the surface end is connected to the inlet of the surface multi-functional coupling unit, as well as the return outlet of the ORC generator set and the heat exchange unit, forming a completely closed circulation loop.

[0039] Pipeline pressure testing and leak detection: After installation, the entire sCO2 pipeline is pressure tested with nitrogen (the test pressure is 1.25 times the design pressure), and the pressure is maintained for 24 hours without leakage. A helium mass spectrometer is then used to detect the sealing of welds and joints.

[0040] S4 is a coupling system installed on the ground, including a compressor, overflow valve, auxiliary pump, throttling valve group and heat exchanger unit, connected to a closed loop, and sensors and flow valves are installed in the pipeline.

[0041] According to an embodiment of the present invention, in step S4, the surface multi-functional coupling unit integrates an intelligent control module. The intelligent control module is connected to a temperature sensor, a pressure sensor, and a flow control valve signal, and is used to automatically adjust the compressor start / stop, auxiliary pump speed, and valve opening according to real-time operating conditions.

[0042] Specifically, the installation of the surface multi-functional coupling unit includes: constructing an equipment foundation on the surface, and sequentially installing a compressor (frequency-controlled, for active pressurization), an overflow valve (for setting a safety relief pressure), an auxiliary pump (centrifugal type, used for supplementing circulation power during startup or at low load), a throttling speed control valve group (including an electric regulating valve and a manual shut-off valve), and a heat exchange unit (plate heat exchanger or shell-and-tube heat exchanger, used for cooling SO2). All equipment is connected to the inlet and outlet of the SO2 circulation loop via pipelines, and bypass pipelines are provided for easy maintenance.

[0043] Sensor and actuator installation includes: installing temperature sensors (PT100, accuracy ±0.1℃), pressure sensors (range 0~20MPa, accuracy 0.5), and flow control valves (electric regulating valves, response time ≤2s) at key nodes of the sCO2 circulation pipeline (including downhole inlet, surface outlet, heat exchanger inlet and outlet, ORC evaporator inlet and outlet, etc.). All sensor signal lines and valve control lines are centrally routed to the surface control cabinet.

[0044] The integrated intelligent control module includes: a PLC or embedded industrial computer installed in the ground control cabinet, with a built-in intelligent control module. This module is connected to all sensors, flow control valves, compressor frequency converters, auxiliary pump frequency converters, and throttle valve actuators, and has data acquisition, logic judgment, automatic adjustment, and remote communication functions.

[0045] The safety interlocking device includes: a pressure safety valve, a low-pressure alarm, and a CO2 leak detection probe (infrared or semiconductor type) installed in the coupling unit, and is linked with the mine's existing ventilation system and CO2 monitoring equipment.

[0046] S5, supercritical carbon dioxide working fluid is injected into the loop to form a thermosiphon self-circulation by utilizing the temperature difference between the downhole heat source and the surface cold source.

[0047] According to one embodiment of the present invention, in step S5, when the temperature difference between the downhole heat source and the surface cold source is insufficient to establish a stable thermosiphon cycle, an initial cycle driving force is provided by an auxiliary pump or compressor, and the system automatically switches to self-circulation mode after the temperature difference is restored.

[0048] Specifically, when charging the sCO2 circulating working fluid and establishing the thermosiphon self-circulation, the system is first evacuated, including: closing all valves, using a vacuum pump to evacuate the closed loop, reducing the absolute pressure of the system to below 100Pa for 30 minutes to ensure that there is no air or moisture residue in the pipeline.

[0049] Then, the working fluid is charged: high-purity (≥99.9%) supercritical carbon dioxide working fluid is charged into the closed loop. The charging amount is calculated and determined according to the pipeline volume and design conditions (pressure 8~15MPa, temperature 30~150℃). Generally, the static pressure of the system reaches the critical pressure (7.38MPa) or higher.

[0050] Next, the initial temperature difference is established, specifically by utilizing the natural temperature difference between the underground heat source (the temperature of the surrounding rock of the mine wall is 40~50℃, and the temperature of the geothermal well outlet is 80~120℃) and the surface cold source (ambient air or cooling water, with a temperature of 5~35℃). This allows the sCO2 to absorb heat in the underground heat exchanger, resulting in an increase in temperature and a decrease in density, and then flow naturally upwards along the pipeline. Upon reaching the surface, it releases heat in the heat exchange unit, causing a decrease in temperature and an increase in density, and then flows naturally downwards back, forming a thermosiphon self-circulation.

[0051] Finally, the auxiliary circulation is started, which includes: if the initial temperature difference is insufficient (such as the surface temperature being too low in winter, causing the sCO2 pressure to be lower than the critical value, or the downhole heat source not being preheated), the auxiliary pump or compressor is started to provide the initial circulation driving force to force the working fluid to flow. After the temperature difference between the downhole heat source and the surface cold source returns to normal (temperature difference ≥ 20℃), it automatically switches to self-circulation mode and shuts down the auxiliary equipment.

[0052] S6 regulates the pressure, flow rate, and temperature of supercritical carbon dioxide through the coupling unit: starting the auxiliary pump or compressor to compensate for the pressure head, adjusting the throttle valve and overflow valve to control the flow rate and pressure, and adjusting the heat exchange unit to control the cooling temperature; at the same time, it extracts low-grade heat from the surrounding rock through the mine wall circuit and transfers the heat to the working fluid through the geothermal well water vapor circulation.

[0053] According to one embodiment of the present invention, in step S6, the cooling medium of the surface heat exchanger unit is mine water, return airflow, surface pond water, or winter ambient air.

[0054] According to one embodiment of the present invention, in step S6, the cooling temperature of supercritical carbon dioxide is precisely controlled by adjusting the surface heat exchange unit to regulate the circulation driving force; when the working conditions of the underground heat source or the surface cold source change, the system adapts to the variable load condition through the dynamic adjustment of the surface multi-functional coupling unit.

[0055] Specifically, pressure and flow regulation includes: real-time monitoring of sCO2 pressure, temperature, and flow data via an intelligent control module. When insufficient circulating head is detected, the auxiliary pump (running at low speed) or compressor (frequency converter) is automatically started to compensate for the head deficiency; the circulating flow rate is controlled by adjusting the throttle valve opening (the target flow range is set according to the ORC rated load); the system's maximum pressure is maintained below the design value (e.g., 15MPa) via the overflow valve; and in case of overpressure, the pressure is automatically released to the gas storage tank or the atmosphere (after safe handling).

[0056] Cooling temperature control includes: adjusting the flow rate of the cooling medium of the surface heat exchanger unit (such as adjusting the speed of the cooling water pump or the valve opening) according to the surface cold source conditions and ORC power generation requirements, and precisely controlling the temperature of sCO2 after cooling (such as cooling to 30~40℃), thereby regulating the magnitude of the circulation driving force - the lower the cooling temperature, the greater the density difference, and the higher the thermosiphon head.

[0057] Downhole heat extraction includes: circulating low-temperature water within the surrounding rock borehole via a circulating water pump in the mine wall circuit, absorbing low-grade heat (40~50℃) from the surrounding rock. This heat is then transferred to the sCO2 main circuit after being raised by an intermediate heat pump (optional); simultaneously, the deep geothermal well water-vapor circulation system directly transfers high-temperature heat (around 100℃) from the well bottom to the sCO2 working fluid via a heat exchanger. The two heat sources can be connected in parallel or series to the sCO2 circuit based on their temperature differences.

[0058] The adaptive adjustment of operating conditions includes: when the temperature of the downhole heat source fluctuates (such as the temperature of the surrounding rock dropping due to mining disturbance) or the surface cold source conditions change (such as diurnal temperature difference and seasonal changes), the intelligent control module automatically adjusts the auxiliary pump speed, throttle valve opening and cooling capacity of the heat exchange unit to maintain the temperature (such as 80~100℃) and pressure (8~12MPa) of sCO2 at the inlet of the ORC evaporator in the optimal efficiency range.

[0059] S7 is an ORC generator set driven by supercritical carbon dioxide at high surface temperature. The waste heat from power generation is used for heating, and the low-temperature working fluid after heat release is returned to the underground cooling tunnel air, realizing the combined production of power generation, heating and cooling.

[0060] According to an embodiment of the present invention, in step S7, the evaporator of the ORC generator set exchanges heat with the supercritical carbon dioxide loop, and the condenser is connected to the surface cooling system; the waste heat of the supercritical carbon dioxide after power generation is first used for heating by the heat exchange unit. When the heating load is lower than the threshold, the excess heat is discharged to the environment through the auxiliary heat dissipation device; the low-temperature supercritical carbon dioxide returning to the well preferentially passes through the roadway air cooler to cool the working face air. When the return liquid temperature is higher than the set threshold, the bypass part of the flow is directly returned to the heat source area.

[0061] According to one embodiment of the present invention, after step S7, when the return liquid temperature of the low-temperature supercritical carbon dioxide returned to the well is lower than a set threshold, the corresponding branch valve is closed, and the circulation is transferred to the next mining area or put into maintenance mode; thus realizing the collaborative operation mode of "extracting heat first and then mining coal".

[0062] Specifically, ORC power generation involves: high-temperature, high-pressure sCO2 (e.g., 100℃, 10MPa) from the surface entering the evaporator of the ORC generator set, transferring heat to the organic working fluid (e.g., R245fa), driving the expander to generate electricity. After releasing heat, the sCO2 cools to a medium temperature (e.g., 60~70℃) and flows out from the evaporator outlet. The electricity output from the ORC generator set is either fed into the mine power grid or used for self-consumption by surface equipment.

[0063] Waste heat heating specifically involves: medium-temperature sCO2 from the ORC evaporator entering the heat exchange unit (heating heat exchanger) to exchange heat with the district heating circulating water, transferring the waste heat to the heating system. The heating outlet water temperature can be adjusted to 45~55℃, used for heating buildings in the mining area or for wellhead frost protection. If the heating load is low, excess heat can be discharged to the environment through auxiliary heat dissipation devices (air-cooled radiators or cooling towers).

[0064] Low-temperature SCO2 reinjection underground specifically includes: further reducing the temperature of the SCO2 after heating and heat release (e.g., to 30-40℃), and returning it underground via the return pipeline. The low-temperature SCO2 is preferentially introduced into the roadway air cooler, where it exchanges heat with the mine roadway air, absorbing air heat and reducing the ambient temperature at the working face (by 5-10℃), thus achieving the mine cooling function.

[0065] Flow distribution and threshold control specifically include: installing a bypass regulating valve in the return liquid pipeline. When the detected return liquid temperature is lower than the set threshold (e.g., 25℃), the corresponding branch valve can be closed, transferring the circulating working fluid to the next mining area or putting it into maintenance mode; when the return liquid temperature is higher than the set threshold (e.g., 45℃), part of the flow is directly returned to the heat source area (mine wall circuit or geothermal well) through the bypass valve to avoid ineffective cooling.

[0066] The specific implementation of the rotation of mining areas and "heat extraction before coal mining" includes: when the temperature of the surrounding rock in a heat extraction area drops to the lower limit of economic heat extraction (such as below 35°C), the valves of the heat exchange pipeline in that area are closed, and the pipeline interfaces are removed or blocked. The roadway section can then be switched to normal coal mining operations, realizing the temporal and spatial coordination of geothermal extraction and coal mining.

[0067] According to one embodiment of the present invention, a safety interlock protection step is also included: when a supercritical carbon dioxide leak is detected or the pipeline pressure exceeds the design range, the main valve of the surface multi-functional coupling unit is automatically closed and the downhole ventilation enhancement program is started.

[0068] Specifically, during system operation, CO2 leak detection probes deployed underground and on the surface continuously monitor the system. Once a concentration exceeding the standard (e.g., exceeding 5000 ppm) is detected, an audible and visual alarm is immediately issued.

[0069] When a leak is detected or the pipeline pressure exceeds the design range (e.g., exceeding 16MPa), the intelligent control module automatically closes the main valve of the surface multi-functional coupling unit, cuts off the sCO2 circulation, and simultaneously starts the downhole ventilation enhancement program (increasing the fan frequency) to quickly dilute the leaked working fluid.

[0070] After troubleshooting and manual confirmation, the system can be restarted by vacuuming and filling to resume operation.

[0071] The following is combined Figure 2 Detailed explanation of the surrounding rock heat extraction pipeline layout method, including the following steps: Step 11: Based on the geothermal gradient of the surrounding rock in the deep coal mine, the roadway layout conditions, and the heat extraction load requirements, determine the range of the heat extraction area, design the borehole spacing, borehole diameter, borehole depth, and the pipe diameter and wall thickness parameters of the inner and outer double-pipe heat exchangers, and determine the working pressure of the circulating water and the target outlet water temperature.

[0072] Step 12: Drill directional holes into the surrounding rock along the sidewall or roof of the tunnel at the designed intervals. The drilling depth is determined based on the thermal influence radius and thermal properties (thermal conductivity, specific heat capacity) of the surrounding rock to ensure that the drilling reaches the target heat-extracting rock layer.

[0073] Step 13: Install a double-tube water exchanger in each borehole. The inner tube is used to inject low-temperature water, and the annular channel between the outer and inner tubes is used for the return of high-temperature water after heat absorption. The outer tube of the double-tube water exchanger adopts a plug-in design—that is, the end of one tube is reduced in diameter or has a socket, and it is directly inserted into the flared end of the adjacent tube. A continuous and closed heat exchange loop is formed by sealing rings or heat fusion, without the need for additional joints. All double-tube heat exchangers in the boreholes are connected in series or in parallel to form a complete underground hot water extraction network.

[0074] Step 14: Connect the inlet main of the underground hot water extraction network to the cold working fluid side outlet of the underground heat pump, and connect the return main to the hot working fluid side inlet of the heat exchanger; install a circulating water pump on the inlet main and a temperature sensor and flow control valve on the return main; connect the temperature sensor, flow control valve and circulating water pump to the intelligent control module of the surface multi-functional coupling unit through signal lines to form an intelligent flow and temperature control system.

[0075] Step 15: Start the circulating water pump to inject low-temperature water into the inner and outer double-tube heat exchanger inside the surrounding rock borehole. The water quickly reaches the bottom of the borehole through the inner tube, and then turns to enter the annular channel between the outer and inner tubes. During the water flow, it continuously absorbs heat from the surrounding rock, and the water temperature rises to a certain temperature. The heated hot water is collected through the return water main and enters the intermediate heat pump, which transfers the heat to the superheat storage tank. The cooled water after releasing heat re-enters the surrounding rock pipe network for heat extraction. During the heat extraction process, the intelligent flow and temperature control system pre-sets the target temperature range of the return water (e.g., 50~55℃) and automatically adjusts the speed of the circulating water pump and the opening of the flow control valve according to the real-time return water temperature, so that the heat extraction of each borehole is uniform and the temperature field of the surrounding rock decreases stably.

[0076] Step 16: When the intelligent flow and temperature control system detects that the return water temperature is consistently lower than the minimum target temperature (e.g., below 35°C, indicating that the surrounding rock thermal resources in the area have been basically exhausted or the heat exchange efficiency is insufficient), the system automatically reduces the frequency of the circulating water pump to the minimum, closes the valves on the inlet and return water mains, and issues a maintenance command; the inner and outer double-tube heat exchangers in the borehole in the area are removed manually or mechanically (pull out the inner and outer tubes), and the branch interface of the main pipe is sealed with a quick-release sealing cap to prevent water leakage.

[0077] Step 17: After the pipeline network of all boreholes in the current heat extraction area has been recovered and the surrounding rock temperature has recovered to below the set threshold (or the working face has no further heat extraction value), the roadway section can be switched to normal coal mining operations to achieve coordinated mining of "heat extraction first, coal mining later" or cooling of the surrounding rock wall.

[0078] The following is combined Figure 3 and Figure 4 Detailed explanation of the surface-mounted unit layout method, including the following steps: Step 21: Based on the actual depth of the coal mine (e.g., above 600 meters) and the geothermal gradient, determine the temperature distribution of the surrounding rock at different depths and the outlet temperature of the deep geothermal well. Based on this, design the pipe diameter, insulation layer thickness, and pipe material of the sCO2 circulation pipeline. At the same time, determine the underground surrounding rock heat extraction area and the location of the deep geothermal well based on the geological conditions, and design the parameters of the sCO2 circulation main pipeline, the surface multi-functional coupling unit, the ORC generator set, and the district heating network.

[0079] Step 22: Bury heat exchange pipes in the mine wall of the mine roadway to form a primary mine cooling circuit; drill geothermal wells deep in the mining area, install heat exchange pipes and heat exchangers in the wells, and establish a closed underground water vapor circulation system for extracting high-temperature geothermal energy.

[0080] Step 23: Lay sCO2 insulated circulation pipelines along the vertical shaft and underground roadways. The underground end is connected to the outlet of the mine wall heat exchange pipeline and the heat exchanger in the geothermal well, and the surface end is connected to the multi-functional coupling unit, ORC generator set and heat exchange unit to form a closed loop.

[0081] Step 24: Install a coupled control system on the ground, including a compressor, overflow valve, auxiliary pump, throttling speed control valve group and heat exchanger unit, and connect it to the inlet and outlet of the sCO2 circulation pipeline; install temperature sensors, pressure sensors and flow control valves at key nodes of the pipeline.

[0082] Step 25: Inject supercritical carbon dioxide working fluid into the closed loop, close all control valves, and put the system in standby mode; utilize the temperature difference between the downhole heat source and the surface cold source to make the density of sCO2 decrease and rise naturally after absorbing heat downhole, and increase in density and sink naturally after releasing heat on the surface, forming a thermosiphon self-circulation; if the initial temperature difference is insufficient to establish a stable cycle, start the auxiliary pump or compressor to provide the initial cycle driving force.

[0083] Step 26: Monitor and adjust the pressure, flow rate and temperature of sCO2 in real time through the surface multi-functional coupling unit: start the auxiliary pump or compressor to make up for the insufficient self-circulation head; adjust the throttle valve and overflow valve to control the circulation flow rate and system pressure; adjust the surface heat exchange unit to accurately control the cooling temperature of sCO2; at the same time, the underground mine wall circuit extracts low-grade heat from the surrounding rock (such as 40~50℃), and the water vapor circulation of the deep geothermal well transfers the heat to sCO2 (such as heating it to about 100℃).

[0084] Step 27: High-temperature sCO2 on the surface drives the ORC generator set to generate electricity. The waste heat after power generation is used for heating the surrounding area through the heat exchange unit. The low-temperature sCO2 after heat release is returned to the mine and is used to cool the air in the mine roadway, realizing the integrated utilization of "power generation - heating - cooling". When the return liquid temperature is lower than the set threshold, the corresponding branch valve is closed and the machine is transferred to the next mining area or put into maintenance mode.

[0085] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0086] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0087] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0088] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for coal mine geothermal extraction power generation and combined heat, power and cooling based on sCO2 cycle, characterized in that, Includes the following steps: S1, determine the heat extraction zone of the surrounding rock in the well and the geothermal well, and design the parameters of the circulation pipeline, surface coupling unit, ORC generator set and heating network; S2, heat exchange pipes are buried in the mine wall to form a cooling loop, and heat exchangers are installed in the geothermal well to establish a closed water-vapor circulation. S3, with insulated pipelines laid along the shaft and tunnel, the lower end of the shaft is connected to the heat exchange pipeline and geothermal heat exchanger, and the surface end is connected to the coupling unit, ORC generator set and heat exchange unit to form a closed loop. S4, a coupling system including a compressor, overflow valve, auxiliary pump, throttling valve group and heat exchanger unit is installed on the ground, connected to a closed loop, and sensors and flow valves are installed in the pipeline; S5, supercritical carbon dioxide working fluid is injected into the loop to form a thermosiphon self-circulation by utilizing the temperature difference between the downhole heat source and the surface cold source; S6 regulates the pressure, flow rate, and temperature of supercritical carbon dioxide through the coupling unit: starting the auxiliary pump or compressor to compensate for the pressure head, adjusting the throttle valve and overflow valve to control the flow rate and pressure, and adjusting the heat exchange unit to control the cooling temperature; at the same time, it extracts low-grade heat from the surrounding rock through the mine wall circuit and transfers the heat to the working fluid through the geothermal well water vapor circulation. S7 is an ORC generator set driven by supercritical carbon dioxide at high surface temperature. The waste heat from power generation is used for heating, and the low-temperature working fluid after heat release is returned to the underground cooling tunnel air, realizing the combined production of power generation, heating and cooling.

2. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S2, the heat exchange pipes in the mine wall are covered with a heat-conducting layer made of polymer or metal materials, and their burial depth and spacing are determined by optimization based on the thermal properties of the surrounding rock. The water-vapor circulation system in the deep geothermal well is a closed loop, and the working fluid is treated mine water or pure water.

3. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S3, the supercritical carbon dioxide insulation circulation pipeline is laid along the vertical shaft using a double-layer insulation structure. The inner layer is a pressure-resistant metal corrugated pipe, and the outer layer is a low thermal conductivity insulation material and a waterproof protective layer, with fixed supports installed at intervals.

4. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S4, the surface multi-functional coupling unit integrates an intelligent control module. The intelligent control module is connected to the temperature sensor, pressure sensor, and flow control valve signal, and is used to automatically adjust the compressor start / stop, auxiliary pump speed, and valve opening according to real-time operating conditions.

5. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S5, when the temperature difference between the downhole heat source and the surface cold source is insufficient to establish a stable thermosiphon cycle, the auxiliary pump or compressor provides the initial cycle driving force, and automatically switches to self-circulation mode after the temperature difference is restored.

6. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S6, the cooling medium of the surface heat exchanger unit is mine water, return airflow, surface pond water, or winter ambient air.

7. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S7, the evaporator of the ORC generator set exchanges heat with the supercritical carbon dioxide loop, and the condenser is connected to the surface cooling system. The waste heat from the supercritical carbon dioxide after power generation is first used for heating by the heat exchange unit. When the heating load is lower than the threshold, the excess heat is discharged to the environment through the auxiliary heat dissipation device. The low-temperature supercritical carbon dioxide returning to the well first passes through the roadway air cooler to cool the working face air. When the return liquid temperature is higher than the set threshold, a portion of the bypass flow is directly returned to the heat source area.

8. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, It also includes safety interlock protection steps: when supercritical carbon dioxide leakage is detected or pipeline pressure exceeds the design range, the main valve of the surface multi-functional coupling unit is automatically shut off and the downhole ventilation enhancement program is activated.

9. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, In step S6, the cooling temperature of supercritical carbon dioxide is precisely controlled by adjusting the surface heat exchange unit to regulate the circulation driving force; when the working conditions of the downhole heat source or the surface cold source change, the system adapts to the variable load condition through the dynamic adjustment of the surface multifunctional coupling unit.

10. The method for coal mine geothermal extraction power generation and combined heat and power (CHP) based on sCO2 cycle according to claim 1, characterized in that, After step S7, when the return liquid temperature of the low-temperature supercritical carbon dioxide returned to the well is lower than the set threshold, the corresponding branch valve is closed, and the circulation is transferred to the next mining area or put into maintenance mode; thus realizing the collaborative operation mode of "extracting heat first and then mining coal".

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