A source network load storage coupling geothermal cascade utilization system

Abstract

This invention discloses a source-grid-load-storage coupled geothermal cascade utilization system. High-temperature geothermal water is extracted from underground and poured into a high-temperature geothermal pool. After distribution, the geothermal water provides a heat source for multi-stage heat exchange devices and the high-temperature end of a thermoelectric generator. The geothermal water releases heat as it flows through the multi-stage heat exchange devices. The first two stages directly supply energy to their corresponding hot water storage tanks and heat load ends. The final stage heat exchange device, paired with a high-temperature heat pump, extracts low-grade heat energy to supply energy to the low-temperature heat load end. Simultaneously, the thermoelectric generator generates electricity using the temperature difference between the high and low temperature pools. The generated electricity is stored in batteries and then used to power the system equipment, creating a self-sustaining closed-loop power supply. Geothermal tailwater is discharged into a low-temperature geothermal pool as a cold source for the thermoelectric generator and then fully reinjected through reinjection wells. This effectively solves the problems of low thermal efficiency, reliance on external power grids, and insufficient protection of geothermal reservoirs in traditional geothermal utilization. It achieves efficient cascade utilization of geothermal resources, self-generation and self-consumption of the system, and sustainable protection of the geothermal reservoir, significantly improving energy supply stability.

Description

Technical Field

[0001] This invention relates to the field of geothermal energy technology, and in particular to a source-grid-load-storage coupled geothermal cascade utilization system. Background Technology

[0002] Geothermal resources, as a renewable energy source with abundant reserves, clean and low carbon emissions, and stable and sustainable operation, occupy a strategic position in the global energy structure transformation and the advancement of "dual carbon" goals. my country possesses superior geothermal resources, with shallow geothermal energy resources equivalent to 19 billion tons of standard coal, and recoverable reserves of medium-deep high-temperature geothermal resources estimated at approximately 2.5 × 10¹⁸. 9 Joules are widely distributed across North China, Northwest China, and Southwest China, providing the basic conditions for large-scale development and utilization. In recent years, with national policy support for clean energy and technological advancements, geothermal utilization has gradually expanded from traditional hot spring tourism and small-scale heating to diverse scenarios such as industrial production, regional energy supply, and agricultural planting, becoming one of the key pathways to replace fossil fuels and reduce carbon emissions. However, despite the enormous potential of geothermal utilization, the industry currently faces numerous technological bottlenecks and systemic defects, severely restricting its large-scale and efficient development, specifically in the following aspects:

[0003] The inefficiency of geothermal energy utilization is low, resulting in significant resource waste. Traditional geothermal utilization systems generally adopt a crude "single-stage heat exchange + single load" model, lacking a design for graded utilization based on the temperature and grade of geothermal resources. For example, medium-deep geothermal water extracted at a temperature of 100-150℃, after passing through a single-stage heat exchanger for building heating (demand temperature 40-60℃), still has a tailwater temperature as high as 50-70℃. However, this tailwater, carrying a large amount of low-grade heat energy, is often directly discharged or subjected to simple treatment without effective recovery. Data shows that the comprehensive utilization rate of thermal energy in existing geothermal utilization projects in my country is generally below 50%, with some small projects even below 35%, far below the international advanced level (above 75%). This model of "high-grade heat energy underutilized and low-grade heat energy wasted" not only results in the idleness of valuable geothermal resources but also indirectly increases the unit energy supply cost and weakens the market competitiveness of geothermal energy.

[0004] The system's operation is highly dependent on external energy sources, significantly diminishing its low-carbon attributes. During geothermal extraction and utilization, core equipment such as water pumps, high-temperature heat pumps, and circulating pumps all require a stable power supply. However, most existing systems rely on the public power grid, lacking independent power supply capabilities. Industry research indicates that electricity consumption accounts for 30%-40% of the operating costs of geothermal projects, with water pumps alone accounting for over 60% of total electricity consumption. For example, a 1 million square meter geothermal heating project consumes approximately 25,000 kWh per day during the winter heating season, exceeding 7 million kWh annually, translating to approximately 4,900 tons of carbon emissions (calculated based on the average carbon emission coefficient of 0.7 kg / kWh for thermal power). This contradicts the core advantage of geothermal "zero-carbon energy supply." Furthermore, the instability of the power grid can lead to frequent equipment start-ups and shutdowns, affecting system operating efficiency and lifespan, further increasing the project's maintenance risks.

[0005] The imperfect protection mechanism for geothermal reservoirs poses challenges to sustainable exploitation. The long-term utilization of geothermal resources depends on the dynamic balance of underground geothermal reservoirs, and reasonable tailwater reinjection is crucial for maintaining reservoir pressure and protecting the geological environment. However, many current projects suffer from immature reinjection technology and low reinjection rates. Some projects lack effective tailwater treatment processes, leading to blockages in reinjection wells due to suspended solids and mineral crystals in the reinjection water, resulting in increased reinjection pressure and decreased flow. Some projects, in an effort to reduce costs, even omit the reinjection process, directly discharging tailwater into surface water or groundwater bodies, causing not only water resource loss but also potential groundwater level decline and reservoir depletion. Statistics show that in some concentrated geothermal heating areas in northern my country, due to long-term disorderly exploitation and low reinjection rates, annual water production from some geothermal wells has decreased at a rate of 5%-10%, and underground reservoir pressure in some areas has dropped by more than 0.5 MPa, even causing slight ground subsidence (annual subsidence of 3-5 mm), seriously threatening the sustainable exploitation of geothermal resources and regional geological safety.

[0006] Poor coordination between geothermal energy sources, grids, loads, and storage leads to insufficient stability and flexibility in energy supply. Geothermal resource extraction is limited by geological conditions, resulting in relatively stable power output, while end-user heat load demand exhibits significant diurnal and seasonal fluctuations. For example, building heating load peaks in winter at 3-5 times the summer peak, with diurnal load fluctuations reaching 20%-30%; industrial heating may experience short-term peak loads due to production plan adjustments. Existing geothermal systems generally lack effective heat and electricity storage buffer units, failing to achieve dynamic matching between heat source output, network transmission, and load demand. During peak load periods in the heating season, insufficient geothermal supply necessitates reliance on fossil fuel equipment such as gas-fired boilers and electric boilers, increasing carbon emissions. During non-heating seasons or periods of low load, excess geothermal resources cannot be stored and are wasted. Furthermore, the lack of coordinated control mechanisms between units, with independent operating parameters for heat exchangers, pumps, and load terminals, makes dynamic adjustment based on real-time conditions difficult, further reducing the system's energy supply reliability and economy.

[0007] The current geothermal systems suffer from limited load adaptability and weak multi-scenario application capabilities. Different end-users have significantly different heat requirements at varying temperature levels: industrial preheating and steam generation require high-temperature heat energy of 80-120℃; commercial building heating and hotel domestic hot water require medium-temperature heat energy of 40-60℃; while agricultural greenhouse insulation and underground garage heating only require low-temperature heat energy of 30-45℃. However, most existing geothermal systems use a uniform heat exchange standard, failing to accurately adapt to the temperature requirements of the load. For example, some projects directly supply 120℃ high-temperature geothermal water to agricultural insulation loads at 35℃, resulting in a serious waste of high-grade heat energy; while some projects attempt to meet the high-temperature process requirements of industrial processes with 50℃ medium-temperature geothermal water, but due to insufficient temperature, they have to consume additional fossil fuels for heating, increasing costs and reducing system efficiency. This "one-size-fits-all" energy supply model makes geothermal systems difficult to adapt to diverse load scenarios, limiting their large-scale promotion in industrial, agricultural, and commercial fields.

[0008] The aforementioned problems are intertwined, preventing the full utilization of geothermal resources and severely hindering the high-quality development of my country's geothermal industry. Therefore, developing a new system capable of achieving efficient cascade utilization of geothermal energy, self-powered closed-loop operation, sustainable protection of geothermal reservoirs, and deep coupling of power generation, grid, load, and storage has become an urgent need for the industry's development. This system holds significant practical importance and strategic value for promoting the large-scale, low-carbon, and sustainable development of the geothermal industry. Summary of the Invention

[0009] To address the aforementioned issues, this invention proposes a source-grid-load-storage coupled geothermal cascade utilization system, aiming to achieve cascade extraction and graded energy supply of geothermal resources according to temperature and quality, maximize the comprehensive utilization rate of thermal energy, construct a self-powered closed loop for the system, reduce dependence on the external power grid, and reduce operating costs.

[0010] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0011] A source-grid-load-storage coupled geothermal cascade utilization system includes:

[0012] A deep geothermal reservoir unit includes a production well, a reinjection well, and an extraction device located below the water surface of the production well.

[0013] The cascade utilization unit includes at least a primary heat exchanger, an intermediate heat exchanger, and a final heat exchanger connected in series via a primary side. The secondary sides of the primary heat exchanger, the intermediate heat exchanger, and the final heat exchanger are respectively connected to the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank. The condenser of the high-temperature heat pump is circulatedly connected to the final hot water storage tank.

[0014] Thermoelectric power generation unit includes a high-temperature geothermal pool, a thermoelectric generator, a low-temperature geothermal pool, and a battery. The evaporator of the high-temperature heat pump is circulatedly connected to the low-temperature geothermal pool. The inlet of the high-temperature geothermal pool is connected to the outlet of the extraction device. The outlet of the high-temperature geothermal pool is connected to the inlet of the primary side of the primary heat exchanger and the high-temperature end of the thermoelectric generator. The power output of the thermoelectric generator is connected to the power input of the battery. The power output of the battery is connected to the power inputs of the high-temperature heat pump and the extraction device. The inlet of the low-temperature geothermal pool is connected to the outlet of the primary side of the final heat exchanger. The outlet of the low-temperature geothermal pool is connected to the reinjection well and the low-temperature end of the thermoelectric generator.

[0015] The load unit includes at least a primary heat load end, a secondary heat load end, and a tertiary heat load end, wherein the primary heat load end, the secondary heat load end, and the tertiary heat load end are respectively circulatedly connected to the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank.

[0016] In some embodiments, the extraction device is a high-temperature submersible pump with a temperature resistance of ≥160℃, the depth of the extraction well is 1500-3000m, and the inner wall of the extraction well is provided with an anti-corrosion and heat-insulating coating; the distance between the reinjection well and the extraction well is ≥500m, and the outlet of the reinjection well is provided with a pressure regulating device, the adjustment range of which is 0.3-0.8MPa.

[0017] In some embodiments, the primary heat exchanger, the intermediate heat exchanger, and the final heat exchanger are all plate heat exchangers with a heat exchange efficiency ≥90%; the inlet water temperature on the primary side of the primary heat exchanger is 90-150℃, and the outlet water temperature is 60-90℃; the inlet water temperature on the primary side of the intermediate heat exchanger is 60-90℃, and the outlet water temperature is 35-60℃; the inlet water temperature on the primary side of the final heat exchanger is 35-60℃, and the outlet water temperature is 20-35℃.

[0018] In some embodiments, the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank are all provided with a polyurethane insulation layer, the thickness of the polyurethane insulation layer is ≥50mm, and the 24-hour heat loss of each hot water storage tank is ≤2%; the volume of the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank is configured according to the corresponding heat load requirements.

[0019] In some embodiments, the tailwater temperature discharged from the low-temperature geothermal pool to the reinjection well is ≤15℃, and the ratio of the reinjection volume of the reinjection well to the geothermal water extraction volume of the extraction well is ≥100%.

[0020] In some embodiments, a power transmission line is also included, wherein the power output terminal of the battery is connected in parallel with the power input terminals of the primary heat load terminal, the secondary heat load terminal, and the tertiary heat load terminal via the power transmission line.

[0021] In some implementations, when the battery charge is ≥90%, the battery is allowed to supply power to the auxiliary electrical equipment at the primary, secondary, and tertiary heat load terminals; when the battery charge is ≤20%, the system automatically switches to the external power grid for supplementary power supply.

[0022] In some embodiments, a heat energy transmission pipeline is also included, which is used to connect the deep thermal storage unit, the cascade utilization unit, the thermoelectric power generation unit, and the load unit. The heat energy transmission pipeline is a polyurethane insulated and corrosion-resistant steel pipe with an insulation layer thickness ≥60mm and a working pressure of 1.0-2.0MPa. Flow, pressure, and temperature monitoring nodes are installed on the heat energy transmission pipeline every 50-100m.

[0023] The beneficial effects of this invention are as follows: By extracting high-temperature geothermal water from underground to a high-temperature geothermal pool, the geothermal water is distributed to provide a heat source for the high-temperature end of a multi-stage heat exchange device and a thermoelectric generator. The geothermal water releases heat by flowing in stages along the multi-stage heat exchange device. The first two stages of the heat exchange device directly supply energy to the corresponding hot water storage tank and the heat load end. The last stage of the heat exchange device, combined with a high-temperature heat pump, extracts low-grade heat energy to supply energy to the low-temperature heat load end. At the same time, the thermoelectric generator generates electricity by utilizing the temperature difference between the high and low temperature pools. The generated electricity is stored in a battery and then used to power the system equipment, thus constructing a self-powered closed loop. The geothermal tailwater is discharged into a low-temperature geothermal pool as a cold source for the thermoelectric generator and then fully reinjected through a reinjection well. Combined with the thermal and electrical storage unit, it achieves deep coupling and regulation of source, grid, load, and storage, effectively solving the problems of low thermal energy utilization efficiency, dependence on external power grid, and insufficient protection of thermal reservoirs in traditional geothermal systems. It realizes the efficient utilization of geothermal resources in stages, self-generation and self-consumption of the system, and sustainable protection of thermal reservoirs, significantly improving the stability of energy supply. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the source-grid-load-storage coupled geothermal cascade utilization system disclosed in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the power generation performance simulation results of the source-grid-load-storage coupled geothermal cascade utilization system disclosed in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram comparing the heat energy utilization rates of conventional technologies and the technical solutions of this invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer and more explicit, the content of this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to this invention are shown in the accompanying drawings, not all of them.

[0028] Example

[0029] This embodiment proposes a source-grid-load-storage coupled geothermal cascade utilization system, such as... Figure 1 As shown, it includes:

[0030] The deep geothermal reservoir unit includes a production well 101, a reinjection well 102, and an extraction device 103 located below the water surface of the production well 101 (e.g., submerged in the geothermal water of the production well 10).

[0031] The cascade utilization unit includes at least a primary heat exchanger 201, an intermediate heat exchanger 202, and a final heat exchanger 203 connected in series on the primary side. The secondary sides of the primary heat exchanger 201, the intermediate heat exchanger 202, and the final heat exchanger 203 are respectively connected to the primary hot water storage tank 204, the intermediate hot water storage tank 205, and the final hot water storage tank 206. Each hot water storage tank is connected in series with the corresponding heat exchanger to form a buffer loop. When the heat load fluctuates, the energy supply pressure is stabilized through the heat storage / heat release function of the hot water storage tank. The condenser of the high-temperature heat pump 207 is circulatedly connected to the final hot water storage tank 206.

[0032] The thermoelectric power generation unit includes a high-temperature geothermal water tank 301, a thermoelectric generator 303, a low-temperature geothermal water tank 302, and a battery 304. The evaporator of the high-temperature heat pump 207 is circulatedly connected to the low-temperature geothermal water tank 302. The following example illustrates a scenario: assuming that after heat exchange between the 45°C hot water on the primary side of the final-stage hot water storage tank 206 and the cold end of the final-stage hot water storage tank 206, the water temperature in the final-stage hot water storage tank 206 does not reach the standard of 40°C. After heat exchange, the water temperature on the primary side of the final-stage hot water storage tank 206 drops to 30°C. It is unreasonable for this 30°C wastewater to enter the low-temperature geothermal water tank 302 (firstly, a large amount of waste heat remains unutilized; secondly, the low-temperature geothermal...). Since the water tank 302 serves as a low-temperature source for thermoelectric power generation, it needs to be kept at a stable low temperature. Therefore, this solution connects the evaporator of the high-temperature heat pump 207 to the low-temperature geothermal water tank 302 in a loop to extract heat from the water in the low-temperature geothermal water tank 302. The condenser of the high-temperature heat pump 207 is connected to the final-stage hot water storage tank 206 in a loop to heat the water in the final-stage hot water storage tank 206. On the one hand, the temperature of the low-temperature geothermal water tank 302 is maintained at a low temperature of 15°C, and on the other hand, the temperature of the final-stage hot water storage tank 206 is controlled at a high temperature of 40°C. The inlet of the high-temperature geothermal water tank 301 is connected to the outlet of the extraction device 103. The outlet of the high-temperature geothermal water tank 301 is connected to the inlet of the primary side of the primary heat exchange device 201 and the high-temperature end of the thermoelectric generator 303. The power output end of the thermoelectric generator 303 is connected to the power input end of the storage battery 304. The power output end of the storage battery 304 is connected to the power input end of the high-temperature heat pump 207 and the extraction device 103. The inlet of the low-temperature geothermal water tank 302 is connected to the outlet of the primary side of the final stage heat exchange device 203. The outlet of the low-temperature geothermal water tank 302 is connected to the reinjection well 102 and the low-temperature end of the thermoelectric generator 303.

[0033] The load unit includes at least a primary heat load terminal 401, a secondary heat load terminal 402, and a tertiary heat load terminal 403. The primary heat load terminal 401 is for high-temperature heating scenarios (such as industrial steam preheating and high-temperature process reactions), requiring a temperature of 60-90℃; the secondary heat load terminal 402 is for medium-temperature heating scenarios (such as commercial building heating and hotel domestic hot water), requiring a temperature of 35-60℃; and the tertiary heat load terminal 403 is for low-temperature heating scenarios (such as agricultural greenhouse insulation and underground garage heating), requiring a temperature of 25-45℃. The primary heat load terminal 401, secondary heat load terminal 402, and tertiary heat load terminal 403 are cyclically connected to the primary hot water storage tank 204, the intermediate hot water storage tank 205, and the final hot water storage tank 206, respectively. Each load terminal is equipped with a flow regulating valve and a temperature feedback sensor to achieve on-demand energy supply control.

[0034] In this scheme, high-temperature geothermal water from the well 101 is extracted to a high-temperature geothermal pool 301 via an extraction device 103. After distribution, it provides a heat source for the primary heat exchange device 201 and the high-temperature end of the thermoelectric generator 303. Then, the geothermal water releases heat by flowing in a stepped manner along the primary side of the multi-stage heat exchange device. The first two stages of the heat exchange device supply energy to the corresponding hot water storage tanks and heat load ends through their secondary sides. The final stage heat exchange device, in conjunction with a high-temperature heat pump 207, extracts low-grade heat energy to supply energy to the final stage hot water storage tank 206 and the tertiary heat load end 403. Furthermore, the thermoelectric generator 303, based on the Seebeck effect, utilizes the temperature difference between the high-temperature geothermal pool 301 and the low-temperature geothermal pool 302. Differential power generation involves multiple P-type and N-type thermoelectric elements connected in series and welded between two ceramic plates to form a TEG module. The high-temperature end of the module is attached to the high-temperature geothermal pool 301, and the low-temperature end is attached to the low-temperature geothermal pool 302. Electrical energy is stored in the battery 304 and supplies power to the extraction device 103 and the high-temperature heat pump 207, forming a self-powered closed loop. Finally, the geothermal tailwater is discharged into the low-temperature geothermal pool 302 through the primary side of the final heat exchange device 203 to provide a cold source for the thermoelectric generator 303. Then, it is fully reinjected into the deep thermal storage unit through the reinjection well 102. At the same time, through the thermal and electrical storage functions of the various levels of hot water storage tanks and the battery, deep coupling and regulation of source, grid, load and storage are achieved. This solution effectively addresses the technical problems of low thermal efficiency, high dependence on external power grid, imperfect geothermal reservoir protection mechanism, poor source-grid-load-storage coordination, and limited load adaptability in traditional geothermal utilization. It realizes efficient cascade utilization of geothermal resources, self-generation and self-consumption of the system, and sustainable protection of the geothermal reservoir, significantly improving energy supply stability and adaptability to multiple scenarios.

[0035] In one example, the extraction device 103 is a high-temperature submersible pump with a temperature resistance of ≥160℃, a rated flow rate of 50-200 m³ / h, and a head of 100-300 m. The depth of the production well 101 is 1500-3000 m, which is suitable for underground high-temperature thermal reservoirs (geothermal water temperature 90-150℃). The inner wall of the production well 101 is equipped with an anti-corrosion and heat-insulating coating. The distance between the reinjection well 102 and the production well 101 is ≥500 m to avoid thermal interference between production and reinjection. The outlet of the reinjection well 102 is equipped with a pressure regulating device with an adjustment range of 0.3-0.8 MPa to prevent damage to the thermal reservoir structure.

[0036] In one example, the primary heat exchanger 201, the intermediate heat exchanger 202, and the final heat exchanger 203 are all plate heat exchangers with a heat exchange efficiency ≥90%. The inlet water temperature on the primary side of the primary heat exchanger 201 is 90-150℃, and the outlet water temperature is 60-90℃. The inlet water temperature on the primary side of the intermediate heat exchanger 202 is 60-90℃, and the outlet water temperature is 35-60℃. The inlet water temperature on the primary side of the final heat exchanger 203 is 35-60℃, and the outlet water temperature is 20-35℃.

[0037] In one example, the primary hot water storage tank 204, intermediate hot water storage tank 205, and final hot water storage tank 206 are all equipped with polyurethane insulation layers, with a thickness ≥50mm, and the 24-hour heat loss of each hot water storage tank is ≤2%. The volumes of the primary hot water storage tank 204, intermediate hot water storage tank 205, and final hot water storage tank 206 are configured according to the corresponding heat load requirements. For example, the volume of the primary hot water storage tank 204 is 50-200m³, the volume of the intermediate hot water storage tank 205 is 30-150m³, and the volume of the final hot water storage tank 206 is 20-100m³. The high-temperature heat pump 207 has a rated heating power ≥50kW and a COP value ≥4.0. Its evaporator is located in the low-temperature geothermal water pool 302 to extract low-grade heat energy from the 30℃ hot water in the low-temperature geothermal water pool 302, and at the same time, it uses the self-generated green electricity of the battery 304 to raise the water temperature of the final hot water storage tank 206.

[0038] In one example, the tailwater temperature discharged from the low-temperature geothermal pool 302 to the reinjection well 102 is ≤15℃, and the ratio of the reinjection volume of the reinjection well 102 to the geothermal water extraction volume of the extraction well 101 is ≥100%, thereby achieving a balance between water resources and pressure in the underground thermal reservoir.

[0039] Even better, both the high-temperature geothermal pool 301 and the low-temperature geothermal pool 302 are equipped with temperature monitoring sensors (measurement accuracy ±0.5℃), with a volume ≥100m³ respectively. The thermoelectric generator 303 consists of 4-8 TEG modules connected in parallel. Each TEG module contains 32 pairs of P-type (Bi2Te3-Sb2Te3) and N-type (Bi2Te3-Bi2Se3) thermoelectric elements. The elements are connected in series and welded between two alumina ceramic plates. The module's thermoelectric conversion efficiency is ≥8%, and the operating temperature difference is 50-120℃. The batteries 3-4 use lithium iron phosphate battery packs with a rated capacity ≥50kWh, a charge / discharge efficiency ≥90%, and are equipped with a battery management system (BMS) to achieve balanced charge / discharge control, providing stable self-generated green electricity for the high-temperature heat pump 207.

[0040] Even better, the high-temperature geothermal water tank 301, the low-temperature geothermal water tank 302, and the various levels of hot water storage tanks (204, 205, 206) integrate an integrated anti-scaling and descaling structure, which specifically includes: a nano anti-scaling coating applied to the inner side of each tank wall with a surface roughness ≤0.8μm to reduce the probability of mineral adhesion; an ultrasonic anti-scaling device installed at the bottom of each tank with a working frequency of 20-40kHz to effectively inhibit calcium and magnesium ion crystallization; and a high-pressure cleaning channel and drain outlet reserved on the side to facilitate the regular removal of deposited dirt, avoid the risk of reduced heat exchange efficiency and pipe blockage caused by scale, and reduce the frequency of equipment disassembly and cleaning.

[0041] Optionally, a power transmission line is also included, with the power output terminal of battery 304 connected in parallel to the power input terminals of primary heat load terminal 401, secondary heat load terminal 402, and tertiary heat load terminal 403 via the power transmission line. More preferably, the power transmission line uses copper core cable, equipped with an inverter (conversion efficiency ≥96%) and a distribution cabinet to realize the conversion of DC power from battery 304 to AC power for equipment use, as well as power supply safety protection.

[0042] Based on the above embodiments, more preferably, when the battery 304 has a charge level ≥ 90%, the battery 304 is allowed to supply power to the auxiliary electrical equipment of the primary heat load terminal 401, the secondary heat load terminal 402 and the tertiary heat load terminal 403; when the battery 304 has a charge level ≤ 20%, the system automatically switches to the external power grid for supplementary power supply.

[0043] In one example, a heat energy transmission pipeline is also included. The heat energy transmission pipeline is used to connect the deep thermal storage unit 1, the cascade utilization unit 2, the thermoelectric power generation unit 3, and the load unit 4. The heat energy transmission pipeline 501 is a polyurethane insulated and corrosion-resistant steel pipe with an insulation layer thickness of ≥60mm and a working pressure of 1.0-2.0MPa. Flow, pressure, and temperature monitoring nodes are installed on the heat energy transmission pipeline 501 at intervals of 50-100m. The monitoring nodes can collect pipeline operating parameters in real time to realize dynamic monitoring of the system operating conditions.

[0044] Application Examples

[0045] 1. System Configuration:

[0046] Deep thermal reservoir unit: production well 101, diameter 300mm, anti-corrosion coating is polyurea; reinjection well 102, diameter 250mm, distance from production well 600m; extraction device 103, rated flow rate 120m³ / h, head 200m, temperature resistance 160℃.

[0047] The cascaded heat exchange unit consists of: primary heat exchanger 201 with a heat exchange area of ​​50 m² and a heat exchange efficiency of 92%; intermediate heat exchanger 202 with a heat exchange area of ​​35 m² and a heat exchange efficiency of 91%; final heat exchanger 203 with a heat exchange area of ​​25 m² and a heat exchange efficiency of 90%; primary hot water storage tank 204 with a volume of 100 m³ and an insulation layer thickness of 60 mm; intermediate hot water storage tank 205 with a volume of 80 m³; final hot water storage tank 206 with a volume of 50 m³; and a high-temperature heat pump 207 with a rated heating power of 42 kW and a COP value of 4.2.

[0048] Thermoelectric power generation unit: Geothermal water tank expansion: High temperature geothermal water tank 301 (volume 120m³) with built-in independent heat exchange chamber; Low temperature geothermal water tank 302 (volume 80m³) with independent circulating water channel.

[0049] TEG Module Selection and Combination: 22 high-performance TEG modules are configured (with 10% redundancy reserved). The specifications of a single module are 200mm×200mm×15mm, containing 48 pairs of P-type (Bi2Te3-Sb2Te3) + N-type (Bi2Te3-Bi2Se3) thermoelectric elements (size 40mm×40mm×4mm), Seebeck coefficient 225μV / K, and rated output power of 3kW per module at a temperature difference of 80℃ (open circuit voltage 28V, rated current 107A, conversion efficiency 8.8%). The modules adopt a "5 series 4 parallel + 2 redundant parallel" structure. 5 modules are connected in series to form 1 group (each group voltage 140V), for a total of 4 groups of working modules + 1 group of redundant modules. All groups are connected in parallel to the combiner box.

[0050] Heat exchange matching design: The high-temperature end of the TEG module is tightly bonded to a 10mm thick nickel-plated copper heat exchange plate. The heat exchange plate has fins (density 10 fins / cm²) on the side in contact with the geothermal water. 22 modules are evenly distributed in the heat exchange chamber of the high-temperature geothermal water tank 301. The low-temperature end is bonded to a stainless steel heat exchange plate and has an independent internal circulating water channel. The high-temperature geothermal water tank 301 is equipped with two circulating pumps with a rated flow of 20m³ / h (one for use and one for standby), and the low-temperature geothermal water tank 302 is equipped with two circulating pumps with a rated flow of 25m³ / h to ensure that the temperature difference between the two ends of the module is stable at 80-90℃.

[0051] Anti-scaling and protection configuration: The heat exchange chamber of the high-temperature geothermal water tank 301 integrates three 30kHz, 500W ultrasonic anti-scaling devices, and the surface of the heat exchange plate is coated with a nano anti-scaling coating (surface roughness 0.6μm); each TEG module has a built-in 150℃ operating temperature fuse, the combiner box has built-in reverse connection protection diodes and overcurrent protection switches, and the output is connected to a 100kW DC / DC converter (conversion efficiency ≥96%).

[0052] Battery pack matching: Configured with two 120V / 500Ah lithium iron phosphate battery packs (parallel, total capacity 1000Ah, charge / discharge efficiency 92%), equipped with a high-performance battery management system (BMS) to achieve balanced charge / discharge control and power regulation; Electric heating network unit: Heat energy transmission pipeline 501 adopts DN200-DN300 insulated and anti-corrosion steel pipe with an insulation layer thickness of 70mm; Power transmission line adopts YJV-10kV copper core cable, equipped with a 100kW inverter and distribution cabinet.

[0053] 2. Operation Process

[0054] Heat source extraction: The extraction device 103 extracts the 120℃ geothermal water from the extraction well 101 to the high-temperature geothermal pool 301 at a flow rate of 120m³ / h.

[0055] High-temperature heat exchange and power generation: The 120℃ geothermal water from the high-temperature geothermal pool 301 is divided into two paths. One path enters the primary heat exchange device 201, where it exchanges heat with the circulating water at the primary heat load end 401. The outlet water temperature is 70℃, and after being stabilized by the primary hot water storage tank 204, it is supplied to the primary heat load end. The other path enters the high-temperature end of the thermoelectric generator 303, where the temperature is maintained at 110℃, providing a heat source for the TEG module. After heat exchange, the water temperature drops to 90℃ and flows into the inlet side of the primary heat exchange device 201. The low-temperature end of the TEG module delivers low-temperature geothermal water (maintained at 15℃) through an independent circulating pump. Based on the Seebeck effect, it generates DC power, which is stabilized to 120V by the combiner box and DC / DC converter and then stored in the battery bank 304. The actual net output power is ≥60kW.

[0056] Medium-temperature heat exchange: The 70°C tailwater from the outlet of the primary heat exchanger 201 enters the intermediate heat exchanger 202 and exchanges heat with the circulating water at the secondary heat load end 402. The outlet water temperature is 45°C. After being stabilized by the intermediate hot water storage tank 205, it is supplied to the secondary heat load end.

[0057] Low-temperature heat exchange and heat pump heating: The 45°C tailwater from the outlet of the intermediate heat exchange device 202 enters the final heat exchange device 203. After initial heat exchange to 30°C, it is heated by the high-temperature heat pump 207 to 40°C. It is then mixed with the hot water in the final hot water storage tank 206 and supplied to the tertiary heat load end 403.

[0058] Thermoelectric power generation cold source and tailwater reinjection: The 15℃ low-temperature tailwater from the outlet of the high-temperature heat pump 207 enters the low-temperature geothermal pool 302, which serves as the low-temperature end of the thermoelectric generator 303, maintaining a temperature of 15℃ and providing a cold source. The TEG module uses the 105℃ temperature difference to generate DC power, which is stored in the battery 304. The tailwater from the low-temperature geothermal pool 302 is pressurized to 0.5MPa by the reinjection pump and then reinjected into the underground thermal reservoir through the reinjection well 102. The reinjection temperature is 15℃, the reinjection volume is 120m³ / h, and the reinjection rate is 100%.

[0059] Self-powered operation: Battery 304 supplies power to the 50kW extraction device 103, the 10kW high-temperature heat pump 207, and the system control equipment, with a self-powering rate of over 90%. When the temperature difference is 105℃, the TEG output power exceeds 60kW, and the BMS automatically switches the excess power to the park's auxiliary loads (such as pipeline heating and backup power supply for reinjection pumps). When the battery 304 charge is ≤20%, it automatically switches to the external power grid for supplementary power supply.

[0060] 3. Performance

[0061] Power generation performance: such as Figure 2 As shown, under the conditions of 120℃ high-temperature geothermal water and 15℃ low-temperature tailwater, the actual output power of the TEG module is 63-65kW. After deducting the DC / DC conversion loss, the net output power is stable at over 60kW, which meets the system's self-power supply and auxiliary power supply requirements.

[0062] Thermal energy utilization rate: such as Figure 2 As shown, the system's total thermal energy utilization rate reaches 96%, which is more than 40% higher than that of traditional single-use systems.

[0063] Operating costs: Annual electricity savings of approximately RMB 1.8 million, a 32% reduction in operating costs, and the TEG module cleaning frequency extended to 15 months, further reducing maintenance costs; Recharge effect: Recharge volume of 120 m³ / h, 100% recharge rate, stable thermal reservoir pressure with no significant attenuation; Power supply stability: The buffering effect of the hot water storage tank and the 304 battery ensures that temperature fluctuations at each load end are ≤±2℃, achieving a power supply reliability of 99%.

[0064] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made based on the essence of the content of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A source-grid-load-storage coupled geothermal cascade utilization system, characterized in that, include: A deep geothermal reservoir unit includes a production well, a reinjection well, and an extraction device located below the water surface of the production well. The cascade utilization unit includes at least a primary heat exchanger, an intermediate heat exchanger, and a final heat exchanger connected in series via a primary side. The secondary sides of the primary heat exchanger, the intermediate heat exchanger, and the final heat exchanger are respectively connected to the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank. The condenser of the high-temperature heat pump is circulatedly connected to the final hot water storage tank. Thermoelectric power generation unit includes a high-temperature geothermal pool, a thermoelectric generator, a low-temperature geothermal pool, and a battery. The evaporator of the high-temperature heat pump is circulatedly connected to the low-temperature geothermal pool. The inlet of the high-temperature geothermal pool is connected to the outlet of the extraction device. The outlet of the high-temperature geothermal pool is connected to the inlet of the primary side of the primary heat exchanger and the high-temperature end of the thermoelectric generator. The power output of the thermoelectric generator is connected to the power input of the battery. The power output of the battery is connected to the power inputs of the high-temperature heat pump and the extraction device. The inlet of the low-temperature geothermal pool is connected to the outlet of the primary side of the final heat exchanger. The outlet of the low-temperature geothermal pool is connected to the reinjection well and the low-temperature end of the thermoelectric generator. The load unit includes at least a primary heat load end, a secondary heat load end, and a tertiary heat load end, wherein the primary heat load end, the secondary heat load end, and the tertiary heat load end are respectively circulatedly connected to the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank.

2. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, The extraction device is a high-temperature submersible pump with a temperature resistance of ≥160℃, the depth of the mining well is 1500-3000m, and the inner wall of the mining well is provided with an anti-corrosion and heat-insulating coating. The distance between the recharge well and the production well is ≥500m, and the outlet of the recharge well is equipped with a pressure regulating device with an adjustment range of 0.3-0.8MPa.

3. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, The primary heat exchanger, the intermediate heat exchanger, and the final heat exchanger are all plate heat exchangers with a heat exchange efficiency of ≥90%. The inlet water temperature on the primary side of the primary heat exchanger is 90-150℃, and the outlet water temperature is 60-90℃. The inlet water temperature on the primary side of the intermediate heat exchanger is 60-90℃, and the outlet water temperature is 35-60℃. The inlet water temperature on the primary side of the final heat exchanger is 35-60℃, and the outlet water temperature is 20-35℃.

4. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, The primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank are all equipped with a polyurethane insulation layer with a thickness of ≥50mm, and the heat loss of each hot water storage tank in 24 hours is ≤2%; the volume of the primary hot water storage tank, the intermediate hot water storage tank, and the final hot water storage tank is configured according to the corresponding heat load requirements.

5. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, The tailwater temperature discharged from the low-temperature geothermal water pool to the reinjection well is ≤15℃, and the ratio of the reinjection volume of the reinjection well to the geothermal water extraction volume of the extraction well is ≥100%.

6. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, It also includes a power transmission line, through which the power output terminal of the battery is connected in parallel with the power input terminals of the primary heat load terminal, the secondary heat load terminal, and the tertiary heat load terminal.

7. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 5, characterized in that, When the battery charge is ≥90%, the battery is allowed to supply power to the auxiliary electrical equipment at the primary, secondary, and tertiary heat load terminals; when the battery charge is ≤20%, the system automatically switches to the external power grid for supplementary power supply.

8. The source-grid-load-storage coupled geothermal cascade utilization system as described in claim 1, characterized in that, It also includes a heat energy transmission pipeline, which is used to connect the deep thermal storage unit, the cascade utilization unit, the thermoelectric power generation unit and the load unit. The heat energy transmission pipeline is a polyurethane insulated and corrosion-resistant steel pipe with an insulation layer thickness of ≥60mm and a working pressure of 1.0-2.0MPa. Flow, pressure and temperature monitoring nodes are installed on the heat energy transmission pipeline every 50-100m.

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