A zoned geothermal-assisted CO2 mineralization sequestration system and method for abandoned deep mines

Abstract

This disclosure relates to the field of carbon dioxide sequestration and comprehensive utilization of deep-earth resources, providing a zoned geothermal-assisted CO2 mineralization sequestration system and method for abandoned deep-earth mines. The system includes: a zoned carbonation reaction unit consisting of underground tunnels and goaf areas, with pre-reaction zones, main mineralization zones, and strongly mineralized zones distributed along the depth; a unit for supplying CO2 and injecting mineralization slurry into the pre-reaction zone; a geothermal heat extraction and supply unit for providing differentiated process heat to each reaction zone; a monitoring and control unit for collecting operating parameters and dynamically adjusting process parameters; and a product output unit for separating and processing products from the strongly mineralized zone. This application achieves the synergistic utilization of deep-earth space, geothermal resources, and CO2 mineralization, improving sequestration efficiency and energy utilization.

Description

Technical Field

[0001] This disclosure relates to the field of carbon dioxide sequestration and comprehensive utilization of deep earth resources, specifically to a zoned geothermal-assisted CO2 mineralization sequestration system and method for abandoned deep earth mines. Background Technology

[0002] Currently, in the fields of carbon dioxide mineralization and storage and reuse of underground mine space, CO2 mineralization, mine solid waste disposal, and geothermal development are typically designed and implemented as independent technical pathways. Existing solutions often treat abandoned mines merely as single storage or conduit spaces, failing to systematically couple their internal structure, geothermal gradient, and mineralization reaction kinetics requirements. Furthermore, the lack of a dynamic matching mechanism between geothermal heat extraction and the temperature conditions required for mineralization reactions leads to problems such as low utilization of low-grade thermal energy, limited reaction rates, and unstable carbon sequestration efficiency.

[0003] Furthermore, the lack of continuous connection between mineralization media injection, reaction process control and product processing makes it difficult to form an efficient, stable and controllable underground in-situ mineralization storage system. Therefore, there is an urgent need for a zoned system and method that can achieve the synergistic integration of deep underground space, geothermal resources and CO2 mineralization process. Summary of the Invention

[0004] To address the problems of existing technologies, such as the lack of synergistic integration between deep-earth mine space, geothermal resources and CO2 mineralization process, mismatch between heat supply and reaction demand, low storage efficiency and uncontrollable operation, this application proposes a zoned geothermal-assisted CO2 mineralization storage system and storage method in deep-earth abandoned mines to achieve multi-resource synergistic utilization, precise heating with differentiated temperatures and dynamic control of the entire mineralization reaction process.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] A zoned geothermal-assisted CO2 mineralization and sequestration system for abandoned deep mines includes: a zoned carbonation reaction unit consisting of an developed underground mine roadway network and goaf, comprising a pre-reaction zone, a main mineralization zone, and a strongly mineralized zone distributed along the depth of the mine and connected by a flow guiding structure, wherein the strongly mineralized zone is equipped with a reflux connection structure for the circulation reaction of incompletely reacted fluids. A CO2 delivery unit, connected to the pre-reaction zone, receives CO2 and pressurizes and delivers it to the pre-reaction zone; a mineralization medium injection unit, its output connected to the pre-reaction zone, injects mineralization medium slurry into the pre-reaction zone; a geothermal heat extraction and supply unit, its supply end thermally coupled to the pre-reaction zone, main mineralization zone, and strong mineralization zone, respectively, configured to provide differentiated process heat with temperature gradients to the pre-reaction zone, main mineralization zone, and strong mineralization zone; a monitoring and control unit, connected to the pre-reaction zone, main mineralization zone, and strong mineralization zone, collects operating status parameters of each reaction zone and sends control commands to the corresponding physical actuators to dynamically adjust process parameters during the reaction process; and a product output unit, its input connected to the fluid output end of the strong mineralization zone, outputs the product to the ground for gas-liquid-solid separation and recovers unreacted CO2. Preferably, the mineralization medium slurry includes wollastonite tailings, thermally activated serpentine tailings, olivine-enriched tailings, and water; the temperature gradients of the pre-reaction zone, main mineralization zone, and strong mineralization zone are configured to match the activation energy of carbonation reactions of different components in the mineralization medium.

[0007] The above scheme divides the abandoned mine space into three functionally distinct reaction zones according to its depth, and combines differentiated heating and closed-loop control mechanisms to ensure that CO2 dissolution, main mineralization reaction and deep conversion take place under suitable thermodynamic and kinetic conditions, respectively. This avoids the problem of incomplete reaction or energy waste in a single temperature range, and achieves efficient synergy between the structured utilization of underground space and the mineralization process.

[0008] As a further improvement of this application, the pre-reaction zone is configured to be located in strata with a burial depth of 800–1100 m and a natural geothermal temperature of 35–48 °C; the main mineralization zone is configured to be located in strata with a burial depth of 1100–1500 m and a natural geothermal temperature of 42.5–60 °C; and the strongly mineralized zone is configured to be located in strata with a burial depth of 1500–2000 m and a natural geothermal temperature of 52.5–75 °C.

[0009] This preferred scheme divides the reaction functional zones according to the natural temperature gradient of the strata, so that the initial thermal environment of each zone matches the target reaction temperature, reducing the external heating load, and providing a reasonable thermodynamic basis for subsequent differentiated temperature increases, thereby improving the overall energy efficiency of the system.

[0010] As a further improvement to this application, the geothermal heat extraction and supply unit includes underground heat exchange components, closed-loop heating pipelines, heat pump units, and heat exchange devices. Preferably, the underground heat exchange components include a first underground heat exchange component, a second underground heat exchange component, and a third underground heat exchange component; the closed-loop heating pipeline includes a first closed-loop heating pipeline, a second closed-loop heating pipeline, and a third closed-loop heating pipeline; the heat pump unit and the heat exchange device are both located within the ground-level heat exchange station; the heat pump unit includes a medium-temperature heat pump and a high-temperature heat pump; the first underground heat exchange component is connected to the pre-reaction zone pipeline via the first closed-loop heating pipeline; the second underground heat exchange component is connected to the medium-temperature heat pump and the heat exchange device pipeline sequentially via the second closed-loop heating pipeline; the third underground heat exchange component is connected to the high-temperature heat pump and the heat exchange device pipeline sequentially via the third closed-loop heating pipeline; a first circulating working fluid is provided in each of the first, second, and third closed-loop heating pipelines; and a second circulating working fluid is provided in the heat exchange device.

[0011] This preferred design facilitates the direct extraction of deep heat from the first underground heat exchange component to supply the pre-reaction zone. Simultaneously, medium-temperature and high-temperature heat pumps are used to upgrade the low-grade heat from the medium-deep layers, meeting the higher temperature requirements of the main and strongly mineralized zones. This creates a three-tiered temperature field that matches the reaction process, avoiding energy mismatch caused by unified heating. Furthermore, this application employs a dual-working-fluid isolation circulation design, ensuring the stability and safety of geothermal extraction while preventing the impact of mine water pollution or scaling on heat exchange efficiency. Centralized ground-based equipment arrangement facilitates maintenance and control, enhancing the long-term reliability of the system.

[0012] As a further improvement to this application, the underground heat exchange component includes one or more of the following: an underground well heat exchanger, a coaxial tube, or a submerged heat exchanger.

[0013] This preferred scheme flexibly selects the heat exchange form according to the heat source characteristics of different parts of the mine, maximizes the utilization of low-grade heat energy in the surrounding rock of the shaft, deep boreholes and mine water, and improves the adaptability and coverage of geothermal collection.

[0014] As a further improvement of this application, a first pressurizing device and a first pressure stabilizing device are provided on the fluid input pipeline of the main mineralization zone for pressurizing and stabilizing the fluid entering the main mineralization zone; a second pressurizing device and a second pressure stabilizing device are provided on the fluid input pipeline of the strong mineralization zone for pressurizing and stabilizing the fluid entering the strong mineralization zone.

[0015] This preferred solution ensures stable flow of the CO2-containing reaction fluid under high pressure by installing a pressurization and stabilization device at the inlet of the critical reaction zone, maintaining sufficient CO2 partial pressure to promote the carbonation reaction rate, while preventing reaction interruption or equipment damage due to pressure fluctuations.

[0016] As a further improvement of this application, the strongly mineralized zone is also provided with a heat exchange structure, which includes a fluid storage and a heat exchange tank.

[0017] This preferred scheme integrates waste heat recovery and unreacted fluid circulation mechanisms in the highly mineralized zone. On the one hand, it reduces the system's dependence on external heat sources through countercurrent heat exchange, and on the other hand, it extends the reaction residence time through reflux, significantly improving CO2 conversion rate and thermal energy utilization efficiency, thereby enhancing the system's self-sufficiency and economy.

[0018] Furthermore, this application also provides a storage method based on the deep abandoned mine zoned geothermal-assisted CO2 mineralization storage system as described above, comprising: S1, injecting mineralization medium slurry and CO2 into the pre-reaction zone to form a reaction fluid; S2, using geothermal heat extraction and supply units to provide differentiated process heat with temperature gradients to the pre-reaction zone, the main mineralization zone, and the strongly mineralized zone respectively; S3, sequentially introducing the reaction fluid in the pre-reaction zone into the main mineralization zone and the strongly mineralized zone for reaction, using a monitoring and control unit to collect the operating status parameters of each reaction zone, and sending control commands to the geothermal heat extraction and supply units and other physical actuators cooperating with them to dynamically adjust the process parameters in the reaction process, wherein the process parameters include at least CO2 delivery rate, mineralization medium injection rate, heat supply to each reaction zone, and fluid return rate; S4. The unreacted reaction fluid is returned to the strongly mineralized zone for recycling reaction, and the fully reacted reaction fluid is output to the product output unit and subjected to gas-liquid-solid separation treatment.

[0019] The above method, through the coordinated action of four steps—zonal feeding, gradient heating, dynamic regulation, and cyclic enhancement—enables the mineralization reaction to proceed step by step under different thermodynamic windows. This ensures both the sufficiency of the reaction and avoids energy redundancy, achieving controllable, efficient, and continuous operation of the sealing process.

[0020] As a further improvement of this application, in step S2, the maintenance temperature and CO2 partial pressure in the main mineralization zone are both higher than those in the pre-reaction zone, and the maintenance temperature and CO2 partial pressure in the strong mineralization zone are both higher than those in the main mineralization zone.

[0021] This preferred scheme creates thermodynamic conditions favorable for the nucleation and growth of carbonate minerals by progressively increasing the temperature and CO2 partial pressure, effectively overcoming the limitation of slow reaction kinetics under low temperature and low pressure, and significantly improving the mineralization rate and the final carbon fixation amount.

[0022] As a further improvement of this application, in step S4, the completely reacted fluid is subjected to countercurrent heat exchange with the second circulating working fluid of the heat exchange device through a fluid storage and heat exchange tank before being output, so as to recover waste heat.

[0023] This preferred solution implements waste heat recovery before product discharge, transferring the sensible heat of the high-temperature fluid to the returned process fluid, reducing the additional energy consumption of the heat pump system, improving the energy utilization efficiency of the entire storage process, and reducing operating costs.

[0024] Beneficial effects: This application constructs a pre-reaction zone, a primary mineralization zone, and a strongly mineralized zone distributed along the depth of the mine, and combines this with a differentiated geothermal heating mechanism to enable the CO2 mineralization reaction to proceed in stages under different thermodynamic conditions. This solves the problem of low conversion rate and high energy consumption caused by the mismatch between temperature and reaction demand in traditional single-reaction zones. The principle lies in utilizing the natural temperature gradient of the formation as the basic heat source, and then precisely supplementing the heat through closed-loop heating pipelines and multi-stage heat pumps to form a temperature field that matches the reaction kinetics, thereby minimizing external energy input while ensuring sufficient reaction.

[0025] This application integrates fluid storage and heat exchange tanks with a reflux connection structure in a highly mineralized zone, enabling the recycling of incompletely reacted fluids and the recovery of waste heat from fully reacted fluids. Based on the non-uniformity of the reaction process and the differences in heat energy grade, this design, through countercurrent heat exchange and closed-loop reflux, extends the effective reaction time to increase the carbon fixation rate and recovers high-grade waste heat to reduce the system's net energy consumption, thus enhancing the economic feasibility and environmental sustainability of the technology.

[0026] This application establishes a closed-loop feedback control mechanism by real-time acquisition of parameters such as temperature, pressure, CO2 concentration, flow rate, and pH through a monitoring and control unit, and dynamically adjusting operations such as heating, material injection, pressurization, and reflux. This mechanism overcomes the uncertainties brought about by the complex and variable underground reaction environment, ensuring stable operation of the system under optimal conditions, improving the reliability and predictability of CO2 sequestration, and providing technical support for intelligent and large-scale carbon sequestration in deep-earth mining spaces. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a zoned geothermal-assisted CO2 mineralization and storage system for deep abandoned mines, according to an embodiment of this application. Figure 2 This is a partial structural diagram of a location of a zoned geothermal-assisted CO2 mineralization and storage system for a deep abandoned mine, according to an embodiment of this application. Figure 3This is a partial structural diagram of another location of a deep abandoned mine zoned geothermal-assisted CO2 mineralization and storage system according to an embodiment of this application.

[0028] In the diagram: 1. CO2 transport unit; 2. Mineralization medium injection unit; 4. Mine zoned carbonation reaction unit; 5. Monitoring and control unit; 6. Product output unit; 31. First underground heat exchange component; 32. Second underground heat exchange component; 33. Third underground heat exchange component; 34. First closed-loop heating pipeline; 35. Second closed-loop heating pipeline; 36. Third closed-loop heating pipeline; 37. Heat pump unit; 38. Heat exchange device; 39. Surface heat exchange station; 41. Pre-reaction zone; 42. Main mineralization zone; 43. Strong mineralization zone; 44. Fluid storage and heat exchange tank; 45. First heat exchange pipeline; 46. Second heat exchange pipeline; 47. Third heat exchange pipeline. Detailed Implementation

[0029] The technical solutions of this disclosure will be clearly and completely described below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0030] To make the above-mentioned objectives, features and advantages of this disclosure more apparent and understandable, the disclosure will be further described in detail below with reference to specific embodiments.

[0031] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1 like Figures 1-3 As shown, this embodiment provides a zoned geothermal-assisted CO2 mineralization and sequestration system for deep abandoned mines. This system aims to achieve efficient carbon dioxide mineralization and sequestration by synergistically utilizing the space of deep abandoned mines and geothermal resources.

[0033] Specifically, the system includes a mine-zoned carbonation reaction unit 4, a CO2 transport unit 1, a mineralization medium injection unit 2, a geothermal heat extraction and supply unit, a monitoring and control unit 5, and a product output unit 6. The mine-zoned carbonation reaction unit 4 is composed of the developed underground mine roadway network and goaf, including a pre-reaction zone 41, a main mineralization zone 42, and a strongly mineralized zone 43, distributed along the mine's depth and connected by a flow guide structure. The strongly mineralized zone 43 is equipped with a reflux connection structure for the circulation of incompletely reacted fluids. In this embodiment, this distribution along the depth is not a simple spatial arrangement, but a functional zoning system constructed based on the deep-earth environmental gradient and the requirements of mineralization reaction kinetics. The pre-reaction zone 41, main mineralization zone 42, and strongly mineralized zone 43 are connected by flow guide channels to achieve the step-by-step downward transport of the mineralization medium slurry. Simultaneously, the reflux channels allow incompletely reacted fluids to return to the previous or current level for enhanced circulation, thus forming a complex flow field structure combining multi-level series and local circulation in physical space. It should be understood that although the diagram shows three independent reaction zones, in actual engineering applications, the boundaries of each zone can be gradual or irregularly distributed according to the actual mine roadway morphology, as long as the logic of functional zoning is met. The mineralization medium slurry includes wollastonite tailings, thermally activated serpentine tailings, olivine-enriched tailings, and water; the temperature gradients of the pre-reaction zone 41, main mineralization zone 42, and strong mineralization zone 43 are configured to match the activation energy of the carbonation reaction of different components in the mineralization medium slurry.

[0034] CO2 conveying unit 1 is connected to pre-reaction zone 41 and is used to receive CO2 and pressurize and convey it to pre-reaction zone 41. The output end of mineralization medium injection unit 2 is also connected to pre-reaction zone 41 and is used to inject mineralization medium slurry into pre-reaction zone 41. Setting the confluence point of CO2 and mineralization medium slurry in pre-reaction zone 41 can utilize the relatively mild thermodynamic conditions of this area to promote the initial mixing and dissolution of the gas, liquid, and solid phases, avoiding equipment erosion or local scaling problems caused by direct mixing under high temperature and high pressure, and laying a uniform material foundation for deep mineralization.

[0035] The heating end of the geothermal heat extraction and supply unit is thermally coupled to the pre-reaction zone 41, the main mineralization zone 42, and the strongly mineralized zone 43, respectively, and configured to provide differentiated process heat with temperature gradients to the pre-reaction zone 41, the main mineralization zone 42, and the strongly mineralized zone 43. The differentiated process heat referred to here means providing heat energy with heat flux matching the thermodynamic requirements of different reaction stages. For example, the pre-reaction zone 41 mainly involves CO2 dissolution and medium wetting, requiring a relatively low temperature; the main mineralization zone 42 is the main site for carbonate mineral nucleation and growth, requiring higher activation energy; while the strongly mineralized zone 43 is dedicated to the deep transformation of difficult-to-react components, typically requiring higher temperatures. Through this differentiated thermal coupling design, this application solves the problem of poor thermodynamic matching caused by unified heating in traditional single reaction zones, avoiding the dual drawbacks of limited reaction rates in low-temperature zones and excessive ineffective energy consumption in high-temperature zones, significantly improving the overall energy efficiency and carbon sequestration efficiency of the system.

[0036] The monitoring and control unit 5 is connected to the pre-reaction zone 41, the main mineralization zone 42, and the strongly mineralized zone 43. It collects the operating status parameters of each reaction zone and sends control commands to the corresponding physical actuators to dynamically adjust the process parameters during the reaction. Specifically, the operating status parameters include, but are not limited to, temperature, pressure, pH value, CO2 concentration, and flow rate. The physical actuators include valves, pump sets, heat pump units, and pressurization devices. This closed-loop feedback mechanism enables the system to cope with the heterogeneity of the deep-earth environment and the nonlinear changes in the reaction process, ensuring that each reaction zone is always maintained within the optimal operating window.

[0037] The input end of product output unit 6 is connected to the fluid output end of the strongly mineralized zone 43, which is used to output the product to the ground for gas-liquid-solid separation and to recover unreacted CO2. Through the organic synergy of the above units, this application constructs a deep-earth integrated energy and chemical system that integrates carbon sequestration, solid waste utilization and geothermal development, realizing the efficient integration and dynamic balance of material flow, energy flow and information flow in deep-earth space.

[0038] Example 2 This embodiment further specifies the geological parameters and differentiated heating architecture of the reaction zones. Specifically, the pre-reaction zone 41 is configured in strata with a burial depth of 800–1100 m and a natural geothermal temperature of 35–48℃; the main mineralization zone 42 is configured in strata with a burial depth of 1100–1500 m and a natural geothermal temperature of 42.5–60℃; and the strongly mineralized zone 43 is configured in strata with a burial depth of 1500–2000 m and a natural geothermal temperature of 52.5–75℃. The burial depth range and natural geothermal temperature range set above are not arbitrarily selected values, but are based on a geological-thermal dual gradient benchmark determined by the coupling of geothermal gradient and CO2 mineralization reaction kinetics requirements in typical mining areas. It should be understood that the above numerical ranges are merely illustrative. In actual engineering applications, the burial depth and temperature boundaries of each region should be adaptively adjusted according to the specific isothermal zone temperature, geothermal gradient, and activation characteristics of the selected mineralization medium slurry in the target mining area, as long as the principle of gradually increasing temperature along the depth direction and matching the heat demand of each stage of reaction is met. By binding the reaction functional zone with the natural stratum temperature field, this application fully utilizes the inherent background heat energy of the deep strata as the basic heat source, significantly reducing the external energy input required to heat the mineralization medium slurry from the ambient temperature to the process temperature, and realizing the source synergy between geothermal resources and the mineralization process.

[0039] Furthermore, in order to construct a precise and controllable process temperature field based on the aforementioned geological zoning, such as Figures 1-3 As shown, the geothermal heat extraction and supply unit includes underground heat exchange components, closed-loop heating pipelines, and a surface heat exchange station 39. The underground heat exchange components include a first underground heat exchange component 31, a second underground heat exchange component 32, and a third underground heat exchange component 33. The closed-loop heating pipelines include a first closed-loop heating pipeline 34, a second closed-loop heating pipeline 35, and a third closed-loop heating pipeline 36. Specifically, the first underground heat exchange component 31 is connected to the pre-reaction zone 41 via the first closed-loop heating pipeline 34; the second underground heat exchange component 32 is connected to the surface heat exchange station 39 via the second closed-loop heating pipeline 35; and the third underground heat exchange component 33 is connected to the surface heat exchange station 39 via the third closed-loop heating pipeline 36. The surface heat exchange station 39 is connected to the main mineralization zone 42 and the strongly mineralized zone 43 via pipelines, configured to maintain a higher temperature in the main mineralization zone 42 than in the pre-reaction zone 41, and a higher temperature in the strongly mineralized zone 43 than in the main mineralization zone 42. Combination Figures 1-3This architecture essentially constructs a three-tiered temperature field that is strictly matched to the reaction process. Specifically, the first underground heat exchange component 31 directly extracts relatively low-temperature geothermal fluids from deep within the environment or extracts heat through a closed-loop system, and then directly transports it to the pre-reaction zone 41 via the first closed-loop heating pipeline 34 to meet the low-grade heat requirements for CO2 dissolution, slurry dispersion, and medium wetting. For the main mineralization zone 42 and the strongly mineralized zone 43, which require higher activation energy, low-grade geothermal energy is collected through the second underground heat exchange component 32 and the third underground heat exchange component 33, respectively. After being upgraded and heated to high-grade process heat by the ground heat exchange station 39, the heat is then transported to the corresponding areas.

[0040] The thermodynamic necessity of adopting the differentiated heating architecture described above in this embodiment lies in the fact that CO2 mineralization and sequestration is a complex process involving multiple series reactions, and the sensitivity of different stages to temperature is drastically different. The pre-reaction zone 41 mainly involves physical dissolution and preliminary chemical wetting; excessively high temperatures would actually reduce the solubility of CO2 in the aqueous phase, therefore, direct supply using medium-low temperature geothermal energy is most suitable. The main mineralization zone 42 is the key stage for carbonate mineral nucleation and crystal growth, requiring higher temperatures to overcome the reaction activation energy barrier and accelerate ion release and precipitation. The strong mineralization zone 43 aims to achieve deep transformation of difficult-to-react components and final fixation of residual CO2, typically requiring the highest temperature within the system to drive the reaction equilibrium towards the product direction. If a single temperature heating method is used, either the reaction rate in the main / strong mineralization zone will be limited and the carbon fixation rate insufficient due to excessively low temperatures, or CO2 will escape from the pre-reaction zone and ineffective energy consumption will increase dramatically due to excessively high temperatures. Therefore, by combining direct supply from underground heat exchange components with heat pump quality improvement and diversion in a three-stage temperature field design, this application achieves a precise match between heat energy grade and reaction requirements, maximizing the overall energy efficiency ratio of the system while ensuring the fullness of the entire chain reaction.

[0041] Example 3 This embodiment further specifies the internal structure of the geothermal heat extraction and supply unit to address the stability and adaptability issues of heat source extraction in complex deep-earth environments. Specifically, the ground heat exchange station 39 is equipped with a heat pump unit 37 and a heat exchange device 38. The heat pump unit 37 includes a medium-temperature heat pump and a high-temperature heat pump. The second underground heat exchange component 32 is connected to the medium-temperature heat pump and the heat exchange device 38 in sequence through a second closed-loop heating pipeline 35. The third underground heat exchange component 33 is connected to the high-temperature heat pump and the heat exchange device 38 in sequence through a third closed-loop heating pipeline 36. The heat exchange device 38 is connected to the pipelines of the main mineralization zone 42 and the strongly mineralized zone 43, respectively. The second closed-loop heating pipeline 35 and the third closed-loop heating pipeline 36 are respectively equipped with a first circulating working fluid. The heat exchange device 38 is equipped with a second circulating working fluid in the pipelines of the main mineralization zone 42 and the strongly mineralized zone 43. The heat exchange device 38 can be a plate heat exchanger. In this embodiment, a medium-temperature heat pump and a high-temperature heat pump are used to upgrade the low-grade geothermal energy delivered to the ground into process heat suitable for the main mineralization zone 42 and the strongly mineralized zone 43, respectively. A plate heat exchanger transfers the process heat from the medium-temperature heat pump and the process heat from the high-temperature heat pump to the second heat exchange pipeline 46 in the main mineralization zone 42 and the third heat exchange pipeline 47 in the strongly mineralized zone 43, respectively. The core of this dual-working-fluid circulation design lies in achieving physical isolation between the geothermal extraction side and the process heat side. It should be understood that waste mine water typically contains high mineralization, acidic components, or suspended particles. If it is directly introduced into the heat pump unit or process reaction system, it can easily lead to equipment corrosion, scaling and blockage, and contamination of the reaction system. In this embodiment, the first circulating working fluid absorbs heat from the closed underground heat exchange components, and the heat is transferred to the second circulating working fluid via a ground heat exchange device. This ensures that the mine water only serves as a heat source medium and does not participate in subsequent process flows, significantly reducing the negative impact of water quality on the core power equipment and the mineralization reaction environment, significantly extending the system's service life and reducing operation and maintenance costs.

[0042] Both the heat pump unit 37 and the heat exchange device 38 are located within the surface heat exchange station 39. This centralized arrangement of high-value precision heat exchange components on the ground not only avoids the corrosive effects of moisture, dust, and corrosive gases from underground, but also provides a safe and convenient operating environment for daily inspections, fault repairs, and component replacements. Furthermore, the centralized ground arrangement eliminates the need for large-scale modifications to underground facilities for capacity expansion or energy efficiency upgrades of the heat pump unit, giving the system exceptional flexibility throughout its entire lifecycle. In the heat transfer path, the medium-temperature and high-temperature heat pumps act as thermal transformers. They extract relatively low-temperature (e.g., 30℃-50℃) geothermal energy from the closed loop, consuming a small amount of electricity to raise its grade to the 100℃-125℃ required for the main mineralization zone 42 and the 135℃-170℃ required for the strongly mineralized zone 43, before efficiently transferring it to the second circulating working fluid via the heat exchange device 38. This tiered quality improvement mechanism makes full use of low-grade geothermal resources and avoids the energy waste caused by directly using high-grade electrical energy for heating, demonstrating a significant improvement in thermodynamic perfection.

[0043] To address the diverse spatial forms and uneven heat source distribution of abandoned deep mines, this embodiment also diversifies the configuration of underground heat exchange components. Specifically, the underground heat exchange components can be selected from one or more of underground shaft heat exchangers, coaxial tubes, or submerged heat exchangers. This multimodal design aims to maximize adaptability to the specific geological and engineering conditions of different mining areas. For example, when the mine has a relatively complete vertical shaft or usable deep boreholes, coaxial tubes are preferred as underground heat exchange components. The counter-current heat exchange structure formed by its annular channel and central tube can efficiently extract heat from the deep surrounding rock, and it occupies a small area and is easy to install. When the mine roadway network is well-developed and the surrounding rock has abundant heat reserves, underground shaft heat exchangers laid along the roadway wall can be used, utilizing the existing roadway surface area as a heat exchange interface to reduce drilling costs. When there is a large amount of water accumulation in the mine goaf and the water has a large heat capacity, submerged heat exchangers can be selected to directly extract heat from the water, making full use of the convective heat transfer characteristics of the water to improve heat extraction efficiency. It should be understood that the aforementioned underground heat exchange components are not mutually exclusive. In actual engineering, they can be combined and applied according to the heat source occurrence at different depths in the mine. For example, shaft heat exchangers can be used in shallow roadway sections, while coaxial tubes can be switched to deep borehole sections, thereby constructing a three-dimensional geothermal collection network. This structural substitutability and combinability not only enhances the universality of the technical solution for various abandoned mines, but also effectively prevents competitors from circumventing the scope of protection of this application by simply changing the type of heat exchanger.

[0044] Example 4 This embodiment further specifies the fluid pressure control mechanism in the reaction zone and the reflux heat exchange composite structure in the strongly mineralized zone 43 to resolve the contradiction between limited reaction kinetics and insufficient thermal energy utilization efficiency during deep mineralization. Specifically, a first pressurizing device and a first pressure stabilizing device are installed on the fluid input pipeline of the main mineralization zone 42 to pressurize and stabilize the fluid entering the main mineralization zone 42; a second pressurizing device and a second pressure stabilizing device are installed on the fluid input pipeline of the strongly mineralized zone 43 to pressurize and stabilize the fluid entering the strongly mineralized zone 43. In this embodiment, the thermodynamic basis for setting the above-mentioned pressurizing and pressure stabilizing devices is that the CO2 carbonation reaction is essentially a chemical reaction process in which the gas volume decreases. According to Le Chatelier's principle, increasing the system pressure is conducive to shifting the chemical equilibrium towards the formation of carbonate solids. At the same time, high pressure conditions can significantly increase the solubility of CO2 in the aqueous phase, thereby increasing the reactant concentration and collision frequency.

[0045] Furthermore, considering the complex underground space of abandoned mines, pressure pulsations are easily generated during long-distance transportation and multi-stage reaction zone flow of fluids. The installation of a pressure stabilizing device can effectively suppress flow field fluctuations, ensuring that the actual residence time distribution of the reaction fluid in each area meets the design expectations and avoiding a decrease in conversion rate due to short-circuit flow or dead zones. It should be understood that although the pressurizing device and the pressure stabilizing device are respectively set at the inlet of the main mineralization zone 42 and the strong mineralization zone 43 in this embodiment, in other embodiments, corresponding pressure regulating components can be added at the outlet of the pre-reaction zone 41 or in the interstage pipeline according to the needs of the process flow, or a multi-stage series pressurization method can be adopted to adapt to the high-pressure conditions at deeper levels. As long as the function of maintaining the CO2 partial pressure in each reaction zone above the target threshold and the flow state is stable can be achieved, it falls within the protection scope of this application.

[0046] As a further improvement to this application, the strongly mineralized zone 43 is also provided with a heat exchange structure, which includes a fluid storage and heat exchange tank 44. Figure 2As shown, the fluid storage and heat exchange tank 44 includes a shell-and-tube heat exchange structure. Its tube side is connected to the output end of the incompletely reacted fluid in the strongly mineralized zone 43, and its shell side is connected to the reflux end of the second circulating working fluid in the heat exchange device 38, enabling waste heat recovery of the fully reacted fluid through counter-current heat exchange. The input end of the reflux connection structure is connected to the fluid output end of the strongly mineralized zone 43, and the output end is connected to the inlet of the strongly mineralized zone 43, used to realize waste heat recovery of the fully reacted fluid and secondary or even multiple reactions of the incompletely reacted fluid. The design intent of this composite structure is to address the nonlinear characteristics of the mineralization reaction and the need for graded utilization of thermal energy. Specifically, due to the differences in the reactivity of the mineralization medium slurry, some difficult-to-react components may not reach the preset conversion rate after a single pass through the strongly mineralized zone 43; direct discharge would result in carbon fixation rate loss. In this embodiment, the incompletely reacted fluid is pumped back to the inlet of the strongly mineralized zone 43 via a reflux connection structure, allowing it to undergo the reaction process again under high temperature and high pressure. This effectively extends the effective residence time without increasing the reactor volume, significantly improving the overall conversion depth of the system. Simultaneously, the high-temperature fluid discharged from the strongly mineralized zone 43 carries a large amount of sensible heat. Directly entering the subsequent product output unit 6 would not only waste energy but could also damage downstream equipment. This embodiment utilizes a counter-current arrangement of a shell-and-tube heat exchanger structure, allowing the high-temperature reaction fluid to flow in the tube side while the low-temperature second circulating working fluid from the ground heat exchange station 39 flows counter-currently in the shell side. The two exchange heat efficiently through the tube walls. This counter-current heat exchange method has a larger average heat transfer temperature difference compared to co-current heat exchange, maximizing the recovery of waste heat from the high-temperature fluid for preheating the fresh working fluid entering the strongly mineralized zone 43, thereby reducing the temperature-raising load of the high-temperature heat pump and improving the overall system's coefficient of performance (COP). It should be understood that although... Figure 2 The diagram shows a shell-and-tube heat exchanger structure as a preferred embodiment. However, in practical engineering, other forms such as plate heat exchangers, spiral plate heat exchangers, or shell-and-tube heat exchangers can be selected according to the fluid properties and installation space, as long as the indirect countercurrent heat exchange function between the reaction fluid and the process working fluid can be achieved. Similarly, the reflux path of the reflux connection structure is not limited to returning to the inlet of this stage. Under specific operating conditions, it can also be designed to return to the previous stage reaction zone or a specific mixing node to adapt to the reaction kinetics characteristics of different mineralization media slurries. Through the synergistic effect of the pressure control and reflux heat exchange composite structure described above, this application achieves internal self-sufficiency and recycling of system energy while ensuring a high carbon fixation rate, enhancing the adaptability and economy of the technical solution in complex deep-earth environments.

[0047] Example 5 This embodiment provides a CO2 mineralization and sequestration method based on the aforementioned deep-earth abandoned mine zoned geothermal-assisted CO2 mineralization and sequestration system. This method is independent of specific system hardware architecture and focuses on achieving efficient and stable CO2 mineralization and sequestration within the deep-earth mine space through time-sequential process steps and dynamic feedback control logic. Specifically, the sequestration method includes the following steps: Step S1: Inject the mineralization medium slurry and CO2 into the pre-reaction zone to form a reaction fluid.

[0048] In this step, the convergence of the mineralization medium slurry and CO2 in the pre-reaction zone 41 is not a simple physical mixing, but a fluid construction process accompanied by mass transfer and preliminary chemical reactions. Specifically, the mineralization medium slurry is prepared on the ground from wollastonite tailings, thermally activated serpentine tailings, olivine-enriched tailings, water, and chemical promoters in a predetermined ratio, and is injected into the pre-reaction zone 41 under pressure; simultaneously, CO2 is captured, compressed, and injected into the same area. Under the relatively mild temperature (e.g., 50-65°C) and pressure conditions in the pre-reaction zone 41, CO2 rapidly dissolves in the aqueous phase to form a carbonate / bicarbonate system, and preliminary wetting and ion release occur on the surface of the mineralization medium particles. Some of the more reactive calcium and magnesium components begin to undergo low-temperature carbonation reactions with dissolved CO2. This process aims to establish a homogeneous liquid-phase carbonation system, improve the dispersion state of the solid medium, and provide a precursor fluid with suitable chemical activity for the subsequent high-temperature main mineralization reaction. It should be understood that although this embodiment describes the method of simultaneously injecting CO2 and mineralizing medium slurry into the pre-reaction zone 41, in other embodiments, a strategy of first injecting mineralizing medium slurry to establish a liquid seal and then injecting CO2, or injecting in stages and alternately, can also be adopted, as long as a CO2-containing reaction fluid that meets the requirements of subsequent reactions can be formed in the pre-reaction zone 41.

[0049] Step S2: Utilize geothermal heat extraction and supply units to provide differentiated process heat with temperature gradients to the pre-reaction zone 41, the main mineralization zone 42, and the strongly mineralized zone 43, respectively.

[0050] This step is crucial for ensuring the kinetic matching of the mineralization reaction. Unlike the traditional single constant-temperature heating mode, this embodiment implements precise heating based on the thermodynamic requirements of each reaction zone. Specifically, deep low-temperature heat energy extracted from underground heat exchange components is directly supplied to the pre-reaction zone 41 to maintain its basic reaction temperature; low-grade geothermal energy collected from closed-loop heating pipelines is upgraded by a medium-temperature heat pump and supplied to the main mineralization zone 42 to maintain it within the main reaction temperature window of 100-125℃; and heat energy further upgraded by a high-temperature heat pump is supplied to the strongly mineralized zone 43 to achieve a deep conversion temperature of 135-170℃. This temperature gradient is established not only to meet the activation energy requirements of each stage of the reaction but also to utilize the natural thermal background of the strata to reduce external energy consumption. In actual operation, the heating process should be started in tandem with the material injection process in step S1, and the output power and circulating working fluid flow rate of each level of heat pump should be dynamically adjusted according to the real-time load to ensure that the reaction fluid can quickly reach the target temperature when entering each zone, avoiding fluctuations in reaction efficiency due to thermal lag.

[0051] Step S3: The reaction fluid in the pre-reaction zone 41 is sequentially introduced into the main mineralization zone 42 and the strongly mineralized zone 43 for reaction. The monitoring and control unit 5 collects the operating status parameters of each reaction zone, and based on this, sends control commands to the geothermal heat extraction and supply unit and other physical actuators that cooperate with it to dynamically adjust the process parameters during the reaction process. Among them, other physical actuators may include all general-purpose pumps, valves, booster devices, reflux equipment, etc. that participate in process regulation, except for the geothermal heating unit.

[0052] This step constitutes the core closed-loop control logic of the method. Driven by pressure, the reaction fluid flows stepwise from the pre-reaction zone 41 to the main mineralization zone 42 and the strong mineralization zone 43. During this process, the monitoring and control unit 5 continuously collects key state parameters such as temperature, pressure, CO2 concentration, flow rate, and pH value in each zone. Unlike a static system structure, this embodiment emphasizes a data-driven real-time dynamic adjustment mechanism. For example, when the actual temperature of the main mineralization zone 42 is detected to be lower than a set threshold, the control system automatically increases the operating frequency of the medium-temperature heat pump or increases the flow rate of the process-side circulating pump to increase the heating capacity. When an abnormal increase in CO2 concentration or a pH value not reaching the preset endpoint is detected at the outlet of the strong mineralization zone 43, the system determines that the reaction is insufficient and immediately issues a command to increase the output temperature of the high-temperature heat pump, or increase the pressure setpoint of the second pressurization device to increase the CO2 partial pressure, or even trigger the reflux mechanism in step S4. Conversely, if the parameters exceed the upper limit, the heating or pressurization intensity is reduced accordingly to prevent over-reaction or equipment overpressure. This dynamic feedback mechanism of perception-decision-execution enables the system to adaptively respond to uncertainties in the underground environment, fluctuations in the properties of mineralized media, and drifts in equipment performance, ensuring that the entire mineralization and storage process is always in the optimal operating range, significantly improving the stability and reliability of storage.

[0053] Step S4: The unreacted reaction fluid is returned to the strongly mineralized zone 43 for recycling reaction, and the fully reacted reaction fluid is output to the product output unit 6.

[0054] This step enhances the reaction depth and diverts the product. Specifically, an online monitoring point is set at the outlet of the strongly mineralized zone 43 to determine whether the fluid has reached the preset reaction endpoint based on the CO2 conversion rate or pH value. For incompletely reacted fluid that has not reached the endpoint, it is pumped back to the inlet of the strongly mineralized zone 43 through a reflux connection structure, allowing it to undergo the reaction process again under high temperature and high pressure until it reaches the target. This cyclic reaction mechanism effectively extends the effective residence time without increasing the reactor volume, which is particularly beneficial for the deep conversion of difficult-to-react components and significantly improves the overall carbon fixation rate. For the fully reacted fluid that has reached the endpoint, it is introduced into the product output unit 6 and transported to the ground for gas-liquid-solid separation. It should be understood that the number of refluxes is not fixed but dynamically determined based on the real-time monitoring data in step S3, for example, it can be set to 2-5 times, or until the outlet indicators are continuously qualified. In addition, before the fluid is output, the residual heat can be recovered using the fluid storage and heat exchange tank 44 for preheating the feed or process fluid, further improving the system energy efficiency. Through the organic connection and dynamic control of the above S1 to S4 steps, this application constructs a continuous, efficient and adaptive deep-earth CO2 mineralization and storage method system.

[0055] Example 6 This embodiment further specifies the gradient temperature and pressure control strategy in step S2 and the countercurrent waste heat recovery operation in step S4 to clarify the underlying mechanism of this method in terms of reaction kinetic matching and system energy efficiency optimization.

[0056] In step S2, the maintenance temperature and CO2 partial pressure in the main mineralization zone 42 are both higher than those in the pre-reaction zone 41, and the maintenance temperature and CO2 partial pressure in the strong mineralization zone 43 are both higher than those in the main mineralization zone 42. This gradient control strategy is not a simple numerical increment, but a thermodynamic driving mechanism built based on the multi-stage kinetic characteristics of the CO2 mineralization reaction. Specifically, the pre-reaction zone 41 is maintained at relatively low temperature (e.g., 50-65°C) and pressure conditions to maximize the solubility of CO2 in the aqueous phase and promote the initial wetting of the mineralization medium surface. This is because excessively high temperatures at this stage would inhibit CO2 dissolution and cause gas escape. When the reaction fluid enters the main mineralization zone 42, the temperature is raised to 100-125°C and the CO2 partial pressure is increased accordingly through the combined action of a medium-temperature heat pump and the first pressurization device. This temperature and pressure window crosses the activation energy barrier for the nucleation and crystal growth of carbonate minerals, significantly accelerating the release rate of calcium and magnesium ions and the precipitation kinetics. In the strong mineralization zone 43, the temperature is further raised to 135-170°C and a higher CO2 partial pressure is maintained through a high-temperature heat pump and the second pressurization device. This is to drive the deep transformation of silicate components (such as serpentine and olivine) that are more reactive at lower temperatures and pressures. At the same time, the high-pressure environment forces the chemical equilibrium to shift towards the solid phase products with reduced volume, thereby ensuring that the final carbon fixation rate meets the target. It should be understood that the specific temperature and pressure values ​​mentioned above are merely illustrative. In actual operation, the temperature and pressure settings for each reaction zone should be adaptively adjusted according to the mineral composition, particle size distribution, and target conversion rate of the selected mineralization medium. As long as a gradient relationship of progressively increasing along the flow direction is met, it falls within the scope of protection of this application. Through this precise gradient temperature and pressure control, this application effectively overcomes the contradictions of slow reaction in the low-temperature zone and high energy consumption and low CO2 solubility in the high-temperature zone in traditional constant temperature and pressure processes, achieving dual optimization of reaction rate and energy utilization efficiency.

[0057] Furthermore, in step S4, before being discharged, the fully reacted fluid undergoes countercurrent heat exchange with the second circulating working fluid of the heat exchange device 38 through the fluid storage and heat exchange tank 44 to recover waste heat. This operation constitutes a key link in the system's internal energy self-sufficiency. Specifically, the fully reacted fluid discharged from the strongly mineralized zone 43 usually still carries high-grade sensible heat above 100°C. Direct discharge would not only waste thermal energy but could also cause thermal shock to subsequent separation equipment. In this embodiment, the high-temperature fluid is introduced into the tube side of the fluid storage and heat exchange tank 44, while the low-temperature second circulating working fluid from the ground heat exchange station 39, which has completed its heating task for the underground reaction zone, is introduced into the shell side. The two form a highly efficient heat exchange interface with countercurrent flow within the tank. Through this countercurrent arrangement, the outlet end of the high-temperature reacted fluid is adjacent to the inlet end of the preheated process working fluid, while the inlet end of the low-temperature process working fluid is adjacent to the outlet end of the reacted fluid to be discharged, thereby maintaining a large average heat transfer temperature difference over the entire heat exchange length and significantly improving the extraction efficiency of waste heat from the reacted fluid. The recovered heat is used to raise the initial temperature of the second circulating working fluid, which returns to the heat pump unit or directly enters the heating pipeline. This directly reduces the compression work required by the high-temperature heat pump to raise the working fluid from ambient temperature to process temperature, significantly improving the system's coefficient of performance (COP). For example, under a preferred operating condition, this countercurrent heat exchange operation can preheat the working fluid entering the strongly mineralized zone 43 by 20-30°C, correspondingly reducing the power consumption of the high-temperature heat pump by approximately 15%-25%. It should be understood that although this embodiment describes a coaxial countercurrent heat exchange as a preferred implementation, in other embodiments, plate heat exchangers, spiral plate heat exchangers, or other equipment capable of achieving indirect countercurrent heat exchange can also be used. As long as the waste heat of the reaction fluid can be effectively transferred to the process circulating working fluid, it should be considered an equivalent substitution to the technical solution of this application. In addition, the operation sequence of the countercurrent heat exchange should be coupled with the reflux judgment logic in step S4. That is, the waste heat recovery path is only opened when the fluid is determined to be fully reacted and ready to be output. For fluids that have not fully reacted and need to be refluxed, the heat exchange structure is bypassed and the reflux connection structure is directly entered to avoid unnecessary heat loss and flow resistance increase, and to ensure the flexibility and economy of the system under variable operating conditions.

[0058] Example 7 This embodiment provides a specific application scenario based on the aforementioned deep-ground abandoned mine zoned geothermal-assisted CO2 mineralization and storage system. The aim is to verify the effectiveness of the technical solution through real-world operating parameters and demonstrate the closed-loop response capability of monitoring and control unit 5 in response to fluctuations in the underground environment. It should be understood that the specific values ​​and operating strategies listed below are merely illustrative and not intended to limit the scope of protection of this application. Those skilled in the art can make adaptive adjustments based on actual mining conditions and process requirements.

[0059] In this application scenario, a typical deep abandoned metal mine was selected as the implementation target. Its stratigraphic isothermal zone temperature is 18℃, and the average geothermal gradient is 3.0℃ / 100m. The system is divided into functional zones along the mine's depth: the pre-reaction zone 41 is located at a depth of 950m, with a natural geothermal temperature of approximately 46.5℃; the main mineralization zone 42 is located at a depth of 1300m, with a natural geothermal temperature of approximately 57℃; and the strongly mineralized zone 43 is located at a depth of 1800m, with a natural geothermal temperature of approximately 72℃. The mineralization medium is prepared by mixing wollastonite tailings, thermally activated serpentine tailings, and olivine-enriched tailings in a mass ratio of 3:4:3. The slurry solid content is controlled at 35%, and the injection flow rate is set at 40m³ / h. 3 / h. CO2 conveying unit 1 operates at a pressure of 8MPa and a flow rate of 2000Nm. 3 A flow rate of / h is supplied to the pre-reaction zone 41.

[0060] After the system starts up and enters steady-state operation, the following process parameters are maintained in each reaction zone: The pre-reaction zone 41 is directly heated by underground heat exchange components, with the temperature stably controlled at 60℃ and the pressure maintained at 8.5MPa. Under these conditions, CO2 solubility is high and the surface of the mineralization medium is well wetted. The main mineralization zone 42 is heated by a medium-temperature heat pump, with the temperature maintained at 115℃ and the pressure increased to 12MPa by the first pressurization device to promote rapid nucleation and growth of carbonate minerals. The strong mineralization zone 43 is heated by a high-temperature heat pump, with the temperature maintained at 150℃ and the pressure increased to 16MPa by the second pressurization device to drive the deep conversion of difficult-to-react silicate components. Under these baseline conditions, online monitoring data at the outlet of the strong mineralization zone 43 shows that the CO2 conversion rate is stable above 90%, and the pH value is maintained in the range of 8.2-8.5, indicating that the reaction system is in its optimal window.

[0061] To verify the system's dynamic control capability, a disturbance causing a decrease in reactivity due to batch fluctuations in the mineralization medium raw materials was simulated. During the 72nd hour of continuous operation, monitoring and control unit 5 detected that the CO2 concentration at the outlet of the strongly mineralized zone 43 exceeded the preset threshold for two consecutive sampling cycles (every 5 minutes), while the pH value dropped to 7.9, indicating incomplete reaction. The system then triggered a closed-loop feedback control mechanism: firstly, the data processing module automatically increased the frequency of the reflux connection structure, raising the reflux flow rate of the incompletely reacted fluid from the initial 20 m³ / s. 3 / h increased to 35m 3This effectively extends the effective residence time by approximately 75%. Secondly, a command is sent to the high-temperature heat pump to temporarily increase its outlet water temperature setpoint from 150℃ to 158℃ to compensate for the loss of reaction kinetic rate. Simultaneously, the replenishment amount of mineralization medium injection unit 2 is fine-tuned, increasing the chemical accelerator dosage by 5%. After approximately 45 minutes of dynamic adjustment, the CO2 concentration at the outlet of the strongly mineralized zone 43 returned to the acceptable range, the pH value recovered to 8.3, and the system continued to operate stably at the new equilibrium point. During this adjustment process, the number of reflux cycles increased from the designed 2 adaptive cycles to 4 cycles, fully demonstrating the robustness of this application in dealing with underground heterogeneity and material fluctuations.

[0062] After the complete operation cycle of this application scenario, the system performance was comprehensively evaluated. The results showed that despite the mid-term disturbance, the average CO2 mineralization and carbon sequestration rate throughout the cycle still reached 92.3%, significantly higher than the 75%-80% level of traditional single-temperature zone processes. In terms of energy efficiency, thanks to the efficient counter-current heat exchange of fluid storage in the strong mineralization zone 43 and heat exchange tank 44, the waste heat recovered from the 150℃ high-temperature products increased the inlet temperature of the second circulating working fluid returning to the ground heat exchange station 39 by 28℃, correspondingly reducing the power consumption of the high-temperature heat pump by about 22%, and the overall waste heat recovery rate of the system reached over 35%. In addition, the solid mineralization products produced by the ground product processing and product output unit 6 were found to meet the carbonate content standards, and the liquid phase was recycled entirely to the pre-reaction zone 41 after simple treatment, realizing the internal circulation of water resources and chemical components. The above data strongly demonstrate that this application, through the synergistic effect of zoned gradient heating, dynamic closed-loop control, and reflux waste heat recovery, can achieve efficient, stable, and low-energy CO2 mineralization and sequestration in complex and variable deep-earth environments.

[0063] Example 8 To further verify the technical advantages of the zoned gradient heating architecture proposed in this application compared to the traditional single-temperature zone heating method, this embodiment sets up a set of comparative tests. These comparative examples aim to simulate common uniform-temperature reaction modes in the prior art, highlighting the unexpected technical effects brought about by the functional decoupling and thermal gradient matching of the pre-reaction zone 41, main mineralization zone 42, and strong mineralization zone 43. It should be understood that these comparative examples are only used to illustrate the technical advancements of this application and are not intended to limit the scope of protection of this application.

[0064] In the comparative example, the same geological conditions of the deep abandoned mine, the mineralization medium formulation (wollastonite tailings, thermally activated serpentine tailings, and olivine-enriched tailings in a mass ratio of 3:4:3, solid content 35%), and the CO2 input parameters (8 MPa, 2000 Nm³) were used as in Example 7. 3The difference lies in that the comparative example eliminates the zoning design along the depth direction, merging the originally independent pre-reaction zone 41, main mineralization zone 42, and strongly mineralized zone 43 into a single continuous reaction chamber, and adopts a unified geothermal heating strategy to maintain the temperature within the entire reaction chamber at a constant 120°C. This temperature value is the typical operating temperature of the main mineralization zone 42 in this embodiment, and is also a commonly used compromise reaction temperature in existing mineralization storage technologies, aiming to represent a conventional technical approach that attempts to balance CO2 dissolution and mineral transformation. The comparative example is also equipped with a pressurization and stabilization device and a product output unit 6, but it does not have a reflux heat exchange composite structure consisting of a fluid storage and heat exchange tank 44 and a reflux connection structure, in order to eliminate the interference of waste heat recovery and circulation enhancement on the core variables, and simply examine the influence of the zonal gradient heating feature.

[0065] Within the same operating cycle, the key performance indicators of the comparative example and Example 7 showed significant differences. Regarding carbon sequestration conversion rate, the average CO2 mineralization carbon sequestration rate of the comparative example was only 68.5%, far lower than the 92.3% of Example 7. In terms of energy consumption per unit of carbon sequestration, the comprehensive power consumption of the comparative example per ton of CO2 stored (mainly from the heat pump and pump unit) was approximately 45% higher than that of Example 7. Regarding effective reaction residence time, although the total volume of the reaction chamber in the comparative example was comparable to the sum of the volumes of the three zones in Example 7, due to the lack of staged control, the actual fluid residence time required to reach the preset conversion endpoint was extended by approximately 30%, and a large number of unreacted fine particles and free CO2 still existed in the outlet fluid.

[0066] The underlying mechanism of these performance disadvantages lies in the inability of a single temperature zone to reconcile the inherent thermodynamic contradictions in the CO2 mineralization process. Specifically, the dissolution of CO2 in the aqueous phase is an exothermic process, and low temperatures are beneficial for improving solubility and gas-liquid mass transfer efficiency; while the carbonation reaction of silicate minerals is an endothermic activation process, requiring high temperatures to overcome the kinetic energy barrier. Under the constant temperature of 120℃ used in the comparative example, for the CO2 dissolution and medium wetting functions that should have been undertaken by the pre-reaction zone 41, this temperature is too high, causing the CO2 dissolution equilibrium to shift to the left, resulting in insufficient concentration of bicarbonate ions in the liquid phase, which leads to a lack of sufficient reactant precursors for subsequent reactions; and for the deep transformation function that should have been undertaken by the strong mineralization zone 43, 120℃ is insufficient to provide the activation energy required for the complete lattice recombination of inert components such as serpentine and olivine, causing the reaction to stagnate at the stage of generating amorphous intermediate products, making it difficult to form stable crystalline carbonates. In contrast, this application utilizes zoned gradient heating, maintaining 60°C in the pre-reaction zone 41 to maximize CO2 capture efficiency, increasing the temperature to 115°C in the main mineralization zone 42 to accelerate nucleation and growth, and further increasing the temperature to 150°C in the strongly mineralized zone 43 to drive deep conversion, so that each reaction stage takes place within its thermodynamically optimal window, thereby achieving a leap in overall performance.

[0067] Furthermore, even attempting to adjust the uniform heating temperature of the comparative process cannot resolve the aforementioned fundamental contradiction. If the comparative temperature is lowered to 60°C to optimize dissolution, the mineral conversion rate will decrease exponentially, causing the carbon fixation rate to drop below 40%. If the temperature is raised to 150°C to promote conversion, the CO2 gas-liquid mass transfer in the inlet section will severely deteriorate, with a large amount of CO2 penetrating the reactor in gaseous form without dissolution. This not only fails to improve the carbon fixation rate but also increases the load and energy consumption of downstream gas separation and recovery. This fully demonstrates that the zoned combined gradient heating scheme of this application is not a simple selection of temperature values, but a systematic reconstruction based on the spatiotemporal distribution characteristics of reaction kinetics. The resulting high conversion rate and low energy consumption are unattainable by single-temperature zone processes, regardless of parameter optimization, exhibiting outstanding substantive characteristics and significant progress.

[0068] The detailed descriptions listed above are merely specific descriptions of feasible implementations of this disclosure and are not intended to limit the scope of protection of this disclosure. All equivalent implementations or modifications made without departing from the spirit of the art of this disclosure should be included within the scope of protection of this disclosure.

Claims

1. A zoned geothermal-assisted CO2 mineralization and sequestration system for deep abandoned mines, characterized in that, include: The mine-zoned carbonation reaction unit consists of an already developed underground mine roadway network and goaf, including a pre-reaction zone, a main mineralization zone, and a strongly mineralized zone distributed along the depth of the mine and connected by a flow guiding structure. The strongly mineralized zone is equipped with a reflux connection structure for the circulation reaction of incompletely reacted fluids. A CO2 conveying unit, which is connected to the pre-reaction zone, is used to receive CO2 and pressurize and convey it to the pre-reaction zone. A mineralizing medium injection unit, the output end of which is connected to the pre-reaction zone, is used to inject mineralizing medium slurry into the pre-reaction zone; A geothermal heat extraction and supply unit, wherein the heat supply end of the geothermal heat extraction and supply unit is thermally coupled to the pre-reaction zone, the main mineralization zone and the strong mineralization zone respectively, and is configured to provide differentiated process heat with temperature gradients to the pre-reaction zone, the main mineralization zone and the strong mineralization zone respectively; The monitoring and control unit is connected to the pre-reaction zone, the main mineralization zone and the strong mineralization zone. It is used to collect the operating status parameters of each reaction zone and send control commands to the corresponding physical actuators to dynamically adjust the process parameters in the reaction process. The product output unit has its input end connected to the fluid output end of the strongly mineralized zone, and is used to output the product to the ground for gas-liquid-solid separation and to recover unreacted CO2.

2. The system according to claim 1, characterized in that, The pre-reaction zone is configured to be located in strata with a burial depth of 800–1100 m and a natural geothermal temperature of 35–48℃; the main mineralization zone is configured to be located in strata with a burial depth of 1100–1500 m and a natural geothermal temperature of 42.5–60℃; and the strongly mineralized zone is configured to be located in strata with a burial depth of 1500–2000 m and a natural geothermal temperature of 52.5–75℃.

3. The system according to claim 1, characterized in that, The geothermal heat extraction and supply unit includes underground heat exchange components, closed-loop heating pipelines, heat pump units, and heat exchange devices.

4. The system according to claim 3, characterized in that, The underground heat exchange components include a first underground heat exchange component, a second underground heat exchange component, and a third underground heat exchange component. The closed heating pipeline includes a first closed heating pipeline, a second closed heating pipeline, and a third closed heating pipeline. The heat pump unit and the heat exchange device are both located in the ground heat exchange station. The heat pump unit includes a medium-temperature heat pump and a high-temperature heat pump. The first underground heat exchange component is connected to the pre-reaction zone pipeline through the first closed heating pipeline; the second underground heat exchange component is connected to the medium-temperature heat pump and the heat exchange device pipeline in sequence through the second closed heating pipeline; and the third underground heat exchange component is connected to the high-temperature heat pump and the heat exchange device pipeline in sequence through the third closed heating pipeline. The first closed heating pipeline, the second closed heating pipeline, and the third closed heating pipeline are each equipped with a first circulating working fluid, and the heat exchange device is equipped with a second circulating working fluid.

5. The system according to claim 4, characterized in that, The underground heat exchange components include one or more of the following: underground well heat exchangers, coaxial tubes, or submerged heat exchangers.

6. The system according to claim 1, characterized in that, The fluid input pipeline of the main mineralization zone is equipped with a first pressurizing device and a first pressure stabilizing device for pressurizing and stabilizing the fluid entering the main mineralization zone; the fluid input pipeline of the strongly mineralized zone is equipped with a second pressurizing device and a second pressure stabilizing device for pressurizing and stabilizing the fluid entering the strongly mineralized zone.

7. The system according to claim 1, characterized in that, The highly mineralized zone is also equipped with a heat exchange structure, which includes a fluid storage tank and a heat exchange tank.

8. A method for the preservation of CO2 mineralization in a zoned geothermal-assisted CO2 mineralization preservation system in deep abandoned mines, characterized in that, include: S1. Inject the mineralizing medium slurry and CO2 into the pre-reaction zone to form a reaction fluid; S2. Geothermal heat extraction and supply units are used to provide differentiated process heat with temperature gradients to the pre-reaction zone, main mineralization zone and strong mineralization zone respectively; S3. The reaction fluid in the pre-reaction zone is sequentially introduced into the main mineralization zone and the strong mineralization zone for reaction. The monitoring and control unit collects the operating status parameters of each reaction zone and sends control commands to the geothermal heat extraction and supply unit and other physical actuators that cooperate with it to dynamically adjust the process parameters in the reaction process. The process parameters include at least CO2 delivery rate, mineralization medium injection rate, heat supply of each reaction zone and fluid return rate. S4. The unreacted reaction fluid is returned to the strongly mineralized zone for recycling reaction, and the fully reacted reaction fluid is output to the product output unit and subjected to gas-liquid-solid separation treatment.

9. The method according to claim 8, characterized in that, In step S2, the maintenance temperature and CO2 partial pressure in the main mineralization zone are higher than those in the pre-reaction zone, and the maintenance temperature and CO2 partial pressure in the strong mineralization zone are higher than those in the main mineralization zone.

10. The method according to claim 8, characterized in that, The system also includes a fluid storage and heat exchange tank and a heat exchange device, wherein a second circulating working fluid is provided in the heat exchange device; in step S4, before the completely reacted fluid is output, it undergoes countercurrent heat exchange with the second circulating working fluid of the heat exchange device through the fluid storage and heat exchange tank to recover waste heat.

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