Method and system for reconstructing liquefied natural gas storage cavern based on abandoned laneway

Abstract

The embodiment of the invention provides a method and system for rebuilding a liquefied natural gas storage cavern based on a waste laneway, and the method comprises the steps: selecting the waste laneway with the surrounding rock stability reaching the standard, and constructing a double airtight barrier; the section of the abandoned laneway is transformed into a trapezoidal structure with a preset angle, and a supporting unit is constructed based on an anchor rod, a concrete lining layer, the surrounding rock and the transformed section; a composite tank wall structure composed of a stainless steel film and a heat preservation layer is laid on the inner surface of a roadway of the abandoned roadway and used for providing heat preservation and double airtight barrier functions and ensuring the sealing performance and heat efficiency of low-temperature liquefied natural gas storage. A process operation platform is arranged at the top of the cavern of the abandoned laneway, and a pump pit is arranged below the process operation platform; an underground water control unit is arranged on the periphery of the reservoir and used for draining rock mass crack water in the construction period and restoring rock mass saturation in the operation period to form a freezing ring. The underground building stability problem of the natural gas storage cavern is solved.

Description

Technical Field

[0001] This application relates to the technical field of converting abandoned shafts and tunnels, specifically to a method and system for converting abandoned shafts and tunnels into liquefied natural gas (LNG) storage facilities. Background Technology

[0002] Currently, the demand for natural gas is growing rapidly. Natural gas storage facilities are mainly constructed using two methods: depleted oil and gas reservoirs and salt caverns. However, the site selection for both is severely limited by geological conditions, resulting in poor site suitability and slow progress in the construction of gas storage facilities.

[0003] Only by rapidly advancing gas storage projects can we regulate the pressure gap in the natural gas pipeline network and ensure natural gas supply. In particular, given the insufficient capacity for liquefied natural gas (LNG), there is an urgent need to reduce the construction costs of new LNG storage facilities. With the continuous growth of global natural gas utilization and the development of storage tank construction technology, the trend towards larger LNG storage tanks is becoming increasingly apparent, with single tank capacities reaching 27×10⁻⁶. 4 The construction technology for cubic meter storage tanks is mature, and the largest underground storage tank has reached 25×10 cubic meters. 4 While the capacity is limited to cubic meters, cryogenic underground liquefied natural gas (LNG) storage, as a novel technology, can achieve a single tank capacity of up to one million cubic meters. Compared to above-ground and underground storage tanks, cryogenic underground LNG storage tanks are safer, more environmentally friendly, and require less land. Their economic advantages become more pronounced as storage capacity increases: the investment for above-ground LNG storage is approximately 10 yuan per cubic meter; for gas reservoir-type storage, it's about 8 yuan per cubic meter; and for underground LNG storage, the investment is expected to drop to 6 yuan per cubic meter. With the increasing construction of LNG receiving terminals along the coast, available port resources are becoming increasingly limited. Cryogenic underground LNG storage utilizes abandoned mine resources, especially in inland areas where mines are widely distributed, offering a wide range of site selection options and promising development prospects. However, this technology is still in its infancy.

[0004] Currently, the conversion of abandoned mine shafts into cryogenic liquefied natural gas (LNG) storage facilities is still in its initial stage both domestically and internationally, with no mature construction cases and a lack of core technologies. Therefore, there is an urgent need to develop construction equipment for converting abandoned mine shafts into cryogenic LNG storage facilities, providing a suitable and optimized solution for utilizing large amounts of abandoned underground space in areas with the most concentrated gas consumption and difficulties in gas storage construction. Summary of the Invention

[0005] This application proposes a method and system for converting abandoned mine shafts into liquefied natural gas storage facilities, which addresses the shortcomings of the prior art.

[0006] According to a first aspect of the embodiments of this application, a method for converting abandoned shafts into liquefied natural gas storage facilities is provided, comprising: Select abandoned shafts and tunnels with acceptable surrounding rock stability and construct double airtight barriers; The cross-section of the abandoned tunnel is transformed into a trapezoidal structure with a preset angle to accommodate the installation requirements of the stainless steel membrane material. A support unit is constructed based on the anchor bolts, concrete lining layer, surrounding rock, and the transformed cross-section to ensure the stability of the tunnel structure and construction safety. A composite tank wall structure consisting of a stainless steel membrane and an insulation layer is laid on the inner surface of the abandoned shaft to provide insulation and a double airtight barrier function and to ensure the sealing and thermal efficiency of cryogenic liquefied natural gas storage. A process operation platform is set on the top of the cavern in the abandoned shaft, and a pump pit for installing a submersible pump is set below the process operation platform. Groundwater control units are deployed around the reservoir to drain fissure water in the rock mass during construction and to restore rock mass saturation to form a cryosphere during operation.

[0007] In some embodiments, the dual airtight barrier includes a first barrier and a second barrier, and constructing the dual airtight barrier includes: The first barrier is constructed as a stainless steel membrane, and the second barrier is constructed as a cryosphere formed by frozen groundwater; An insulation layer, a waterproof layer, and a concrete lining layer are provided between the first barrier layer and the second barrier layer.

[0008] In some embodiments, the method further includes: A pleated structure is provided on the surface of the stainless steel film, and the pleat spacing of the pleated structure is 400-700 mm.

[0009] In some embodiments, the abandoned shaft with satisfactory surrounding rock stability is a main shaft with a gentle slope, and the modification of the cross-section of the abandoned shaft into a trapezoidal structure with a preset angle includes: The weak support areas of the abandoned tunnel are reinforced with anchor bolts and grouting. The anchor bolt holes and grouting holes are arranged at a preset interval and the depth of the anchor bolt holes and grouting holes is greater than the size of the tunnel structure. The abandoned shaft was lined with reinforced concrete to form the concrete lining layer.

[0010] In some embodiments, the slope of the gentle slope tunnel does not exceed 5%, the corner angles of the trapezoidal structure are limited to 90° and 135°, the length of the anchor bolt is 2.5 meters, the spacing between the anchor bolts is 1.5 meters × 1.5 meters, and the thickness of the concrete lining layer is not less than 100 millimeters.

[0011] In some embodiments, the insulation layer is composed of plywood, polyurethane foam, elastic sealant, and a moisture-proof layer from the inside out; the method further includes: The moisture-proof layer is applied to the concrete wall to prevent water vapor penetration.

[0012] In some embodiments, the groundwater control unit includes an upper water replenishment subunit and a lower drainage subunit, and the deployment of the groundwater control unit around the reservoir includes: The water supply holes of the upper water supply subunit and the drainage holes of the lower drainage subunit are arranged in a ring within a predetermined distance range around the cavern of the storage tank.

[0013] In some embodiments, the process operation platform and the tank wall structure of the pump pit that contact the liquefied natural gas are both composite tank wall structures composed of a stainless steel membrane and the insulation layer.

[0014] According to a second aspect of this application, a system for converting abandoned shafts into liquefied natural gas storage facilities is provided, comprising: The dual-barrier construction module is used to select abandoned shafts and tunnels with acceptable surrounding rock stability and construct dual airtight barriers. The tunnel section modification module is used to modify the cross-section of the abandoned tunnel into a trapezoidal structure with a preset angle to adapt to the installation requirements of the stainless steel membrane material, and to construct a support unit based on anchor bolts, concrete lining layer, surrounding rock and the modified cross-section to ensure the stability of the tunnel structure and construction safety. The roadway surface paving module is used to lay a composite tank wall structure consisting of a stainless steel membrane and an insulation layer on the inner surface of the roadway in the abandoned mine roadway, in order to provide insulation and a double airtight barrier function and ensure the sealing and thermal efficiency of the cryogenic liquefied natural gas storage. The operating platform and pump pit construction module is used to set up a process operating platform on the top of the cavern in the abandoned shaft, and to set up a pump pit for installing a submersible pump below the process operating platform. The water control unit deployment module is used to deploy groundwater control units around the reservoir, which are used to drain the fissure water in the rock mass during the construction period and to restore the rock mass to saturation during the operation period to form a cryosphere.

[0015] In some embodiments, the system further includes: The integrated tank wall structure includes, from the inside out, the stainless steel membrane, the insulation layer, the reinforced concrete lining layer, and the surrounding rock; Vapor phase pipeline and feed pipe are used to connect to the storage tank.

[0016] The beneficial effects of the method and system for converting abandoned mine shafts into liquefied natural gas storage facilities according to the embodiments of this application include at least the following: This application embodiment effectively utilizes existing geological conditions to reduce the risk of LNG storage construction by selecting abandoned shafts with acceptable surrounding rock stability and constructing a double airtight barrier, ensuring long-term structural stability and operational safety. Simultaneously, the dual sealing design of stainless steel membrane and cryosphere significantly improves the leak-proof performance of LNG storage. By modifying the cross-section of the abandoned shaft into a pre-defined trapezoidal structure to accommodate the installation of the stainless steel membrane, precise deployment and sealing integrity of the membrane material are ensured. The support unit integrates the self-stabilizing capacity of the surrounding rock with reinforcement measures, strengthening the cavern structure support, preventing the risk of collapse during construction, and ensuring operational safety. Furthermore, by laying a composite tank wall structure on the inner surface of the tunnel, utilizing stainless steel... The synergistic effect of the membrane and insulation layer achieves efficient thermal insulation to reduce liquefied natural gas evaporation loss. The dual airtight barrier mechanism enhances the overall sealing performance and optimizes the thermal efficiency and operational reliability of the low-temperature storage environment. The process operation platform set up at the top of the cavern facilitates equipment installation and maintenance, improving maintenance convenience. The design of the pump pit below supports the stable installation of submersible pumps, ensuring the continuity and operational efficiency of the liquefied natural gas transportation process. By deploying groundwater control units to drain fissure water during construction to create a dry construction environment, water pressure interference is reduced. During operation, the rock mass is restored to saturation to form a cryosphere, and the natural freezing barrier enhances the sealing effect, reducing the need for long-term maintenance. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of a method for converting abandoned shafts into liquefied natural gas storage facilities according to an embodiment of this application. Figure 2 This is a schematic diagram of underground site selection for converting abandoned shafts into liquefied natural gas storage facilities, as described in an embodiment of this application. Figure 3 This is a schematic diagram of the construction of a liquefied natural gas storage facility based on the conversion of abandoned shafts and tunnels, according to an embodiment of this application. Figure 4 This is a cross-sectional schematic diagram of the modified abandoned shaft cryogenic liquefied natural gas storage facility according to an embodiment of this application; Figure 5 This is a schematic diagram of the structure of the stainless steel film pleats in an embodiment of this application; Figure 6 This is a schematic diagram of the structure of the insulation layer in an embodiment of this application; Figure 7 This is a schematic diagram of the operating platform according to an embodiment of this application; Figure 8 This is a schematic diagram of the system for converting abandoned shafts into liquefied natural gas storage facilities, according to an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed embodiments of the present application, but merely to illustrate selected embodiments of the present application. Other embodiments obtained by those skilled in the art based on the embodiments of the present application without inventive effort are all within the scope of protection of the embodiments of the present application.

[0020] It can be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of the embodiments of this application, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a preset orientation, or be constructed and operated in a preset orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0022] This application discloses a method for converting abandoned mine shafts into liquefied natural gas (LNG) storage facilities, which is executed by a system based on the conversion of abandoned mine shafts into LNG storage facilities. (See attached document.) Figure 1 As shown, the method includes steps 110-150.

[0023] Step 110: Select abandoned shafts and tunnels that meet the surrounding rock stability standards, and construct double airtight barriers.

[0024] Among them, the abandoned mine shafts that meet the surrounding rock stability standards are main roadways with gentle slopes, specifically referring to the main roadways in the mining system that undertake the main transportation or ventilation functions. This application prioritizes main roadways with good surrounding rock stability and uses them as the core passageways of the mine; meeting the stability standards means that they must meet the stability and volume requirements for the liquefied natural gas storage facility renovation.

[0025] In some implementations, the dual airtight barrier includes a first barrier and a second barrier.

[0026] In some embodiments, the construction of the dual airtight barrier includes: constructing the first barrier as a stainless steel membrane, and constructing the second barrier as a cryosphere formed by frozen groundwater. The stainless steel membrane is made of Mark III stainless steel or NO96 Invar steel, with a thickness of 1.2-1.5 mm.

[0027] In some implementations, an insulation layer, a waterproof layer, and a concrete lining layer are provided between the first barrier and the second barrier to achieve the function of storing liquefied natural gas at low temperature and in a sealed manner.

[0028] In some embodiments, the method further includes: providing a pleated structure on the surface of the stainless steel film, wherein the pleat spacing of the pleated structure is 400-700 mm.

[0029] For example, a traffic shaft may be constructed in the target area adjacent to the main roadway to serve as a pipeline access route for subsequent cryogenic liquefied natural gas storage facilities. This target area can be determined based on the actual construction conditions.

[0030] Step 120: The cross-section of the abandoned tunnel is transformed into a trapezoidal structure with a preset angle to accommodate the installation requirements of the stainless steel membrane material. Based on the anchor bolts, concrete lining layer, surrounding rock, and the transformed cross-section, a support unit is constructed to ensure the stability of the tunnel structure and construction safety.

[0031] In some embodiments, transforming the cross-section of the abandoned shaft into a trapezoidal structure with a preset angle includes: constructing anchor bolt supports and grouting reinforcement in the weak support areas of the abandoned shaft; and lining the abandoned shaft with reinforced concrete and generating the concrete lining layer.

[0032] For example, the anchor bolt holes and grouting holes are arranged at a preset interval, and the depth of the anchor bolt holes and the grouting holes is greater than the size of the cavern structure.

[0033] For example, engineering practice uses percentage slope rather than angle, and the slope of the gentle slope tunnel does not exceed 5% (for example, the vertical height change range does not exceed 5 meters for every 100 meters of horizontal distance) to reduce the difficulty of reconstruction, and the slope is best when it is close to 0°.

[0034] For example, the corner angles of the trapezoidal structure are limited to 90° and 135°. For instance, when converting abandoned mine shafts into cryogenic liquefied natural gas storage facilities, due to the installation angle limitations of the sealing stainless steel membrane, the mine shafts need to be excavated or filled into a trapezoidal structure, with the angles of each side controlled to 90° and 135°. During support, the self-stabilizing capacity of the surrounding rock and the existing support structure are fully utilized, supplemented by support methods such as anchor bolts and concrete lining.

[0035] For example, the anchor bolt is 2.5 meters long and the anchor bolts are spaced 1.5 meters by 1.5 meters; the thickness of the concrete lining layer is not less than 100 millimeters.

[0036] It is worth noting that, in this application embodiment, the stability of the surrounding rock and the durability of the support structure were assessed before the abandoned mine shaft was renovated. Based on anchor bolt support and grouting reinforcement measures, the weakness of the support structure during mining was avoided. After the abandoned mine shaft underwent the above reinforcement treatment, a stainless steel membrane was used as the first barrier for the airtightness of the tank, and frozen groundwater (cryosphere) as the second airtightness barrier. An insulation layer, a waterproof layer, and a concrete lining layer were respectively installed between the two barriers to achieve the function of low-temperature, sealed storage of liquefied natural gas. Furthermore, the above parameters can be calculated based on the actual construction scale and land acquisition area during application, and the working pressure, diameter, and layout scheme of the gas storage chamber can be further determined.

[0037] In one specific exemplary embodiment, reference is made to the appendix. Figure 2 As shown, an abandoned mine shaft was selected and converted into a medium-sized test chamber with a volume of 60 cubic meters. The slope of the main shaft was approximately 3‰. About 200 meters from the main shaft, there was an auxiliary shaft leading directly to the surface, which could serve as a passage for subsequent process pipelines. Before the conversion of the abandoned mine shaft, the stability of the surrounding rock and the durability of the support structure were assessed. For example, anchor bolt support and grouting reinforcement measures were adopted to improve the weak support structure during mining. The spacing between rows and rings of anchor bolt holes and grouting holes was 2 meters. The depth of anchor bolt holes and grouting holes should be greater than the height or span of the chamber. The drilling length was typically 4-5 meters, and ordinary Portland cement was preferred as the grouting material. (See attached diagram.) Figure 3 As shown, after the abandoned shaft is reinforced, a stainless steel membrane is used as the first barrier to ensure the airtightness of the tank, and frozen groundwater (cryosphere) is used as the second barrier. An insulation layer, a waterproof layer, and a concrete lining layer are installed between the two barriers to achieve the function of low-temperature, airtight storage of liquefied natural gas.

[0038] In this application embodiment, the self-stabilizing capacity of the surrounding rock and the existing support structure can be fully utilized during support, supplemented by support methods such as anchor bolts and lining concrete. In addition, due to the limitations of existing materials, in order to reduce the difficulty and cost of procurement and maintenance, this application transforms the original cross-section of the abandoned shaft into a trapezoidal roof by excavation or filling with lining concrete.

[0039] In one specific exemplary embodiment, refer to the appendix Figure 4As shown, the top of the abandoned shaft was remodeled into a trapezoidal roof using concrete lining, and the lost storage space was compensated by widening the shaft floor. Calculations showed that the shaft floor needed to be excavated vertically downwards by 0.2 meters. The original shaft cross-section was approximately 2.7 meters wide × 2.9 meters high. After the renovation, the perimeter of the storage space cross-section was approximately 7.55 meters, the net area was approximately 3.88 square meters, the effective storage area was approximately 3.06 square meters, and the 6-cubic-meter medium-sized experimental chamber was approximately 19 meters long. The support fully utilized the self-stabilizing capacity of the surrounding rock and the existing support structure, supplemented by anchor bolts and concrete lining. This can be specifically divided into initial support and secondary lining. Initial support included the excavation of the operating platform, pump pit, and sealing plug keyway, followed by anchor bolt support using C22 anchor bolts. No anchor bolt support was used during the shaft floor excavation. All anchor bolts are full-length bonded cement mortar anchor bolts, with a protective layer thickness of not less than 20 mm. Each bolt is equipped with a steel washer and a nut (the nut must be tightened after installation). The anchor bolts are ordinary mortar anchor bolts made of HRB400 grade hot-rolled steel bars, with 50 mm of the end exposed. The cement mortar used for the anchor bolts is M25 grade. The steel washer is made of Q235B steel, with dimensions of 150×150×8 mm, and is secured with an M22 nut. The secondary lining includes: a reinforced concrete lining layer approximately 100 mm thick in the shaft / tunnel, using C30 low-temperature concrete and low-temperature steel bars, with a minimum protective layer thickness of 40 mm. The reinforced concrete lining layer for the operating platform is approximately 350 mm thick. The lining concrete can be prefabricated in the factory and assembled on-site, or poured on-site, depending on the construction conditions. A construction joint should be reserved every 6 meters of lining concrete, and waterproofing treatment should be applied.

[0040] Step 130: A composite tank wall structure consisting of a stainless steel membrane and an insulation layer is laid on the inner surface of the abandoned shaft tunnel to provide insulation and a double airtight barrier function and to ensure the sealing and thermal efficiency of cryogenic liquefied natural gas storage.

[0041] In this context, the inner surface of the abandoned shaft refers to all inner surfaces, including the bottom, walls, and top of the shaft.

[0042] In some embodiments, the insulation layer is composed of plywood, polyurethane foam, elastic mortar, and a moisture barrier layer from the inside out. Polyurethane foam, due to its high thermal resistance, is used as the main insulation component. The polyurethane foam thickness is approximately 200 mm, thereby controlling the temperature of the insulation structure between the membrane and the concrete wall, as well as the temperature of the concrete structure, to be no lower than -50°C.

[0043] In some embodiments, the method further includes applying the moisture barrier to the concrete wall to prevent water vapor penetration.

[0044] For example, the stainless steel membrane is made of Mark III stainless steel or NO96 Invar steel, with a thickness of 1.2-1.5 mm. The insulation layer consists of plywood, polyurethane foam, elastic mortar, and a moisture-proof layer. The bottom, walls, and top of the tunnel all adopt a structure of stainless steel membrane and insulation layer. The tank wall structure, from the inside out, consists of stainless steel membrane, insulation layer, reinforced concrete lining layer, and surrounding rock, mainly relying on the two sealing designs of stainless steel membrane and cryosphere. The stainless steel membrane can be used only to contain liquefied natural gas and does not bear the load independently; the pressure of the liquefied natural gas is borne by the lining wall and surrounding rock. The stainless steel membrane is made of Mark III stainless steel or NO96 Invar steel, with a thickness of 1.2-1.5 mm. The stainless steel membrane has a pleated structure with a pleat spacing of 400-700 mm, as shown in the attached diagram. Figure 5 As shown, the film structure, formed by mold pressing, possesses ductility and can absorb shrinkage deformation under low-temperature conditions. The stainless steel membrane's sealing function includes, but is not limited to: the inner stainless steel film possesses both liquid and airtightness, its form being a double-layered orthogonal corrugated grid, functioning similarly to a bellows, allowing for bidirectional contraction / expansion under varying temperature conditions. The inner film is composed of stainless steel film sheets welded to the protective layer, with the film sheets overlapping and welded together. The entire inner film is densely welded to ensure the airtightness of the maintenance system.

[0045] For example, refer to the appendix. Figure 6 As shown, the insulation layer consists of plywood, polyurethane foam, elastic sealant, and a moisture barrier. Polyurethane foam, with its high thermal resistance, is the primary insulation component, approximately 200 mm thick. The plywood layers above and below the polyurethane foam provide a secure connection. The elastic sealant is used for leveling the concrete wall and connecting the wall to the plywood. The moisture barrier (approximately 2.5 mm thick) is applied to the concrete wall and is airtight, preventing liquid water or water vapor from penetrating the insulation layer during use. The functions of the insulation layer include, but are not limited to: ensuring the concrete structure remains at a temperature no lower than -50°C through the insulation structure between the membrane and the concrete wall; and transferring the lateral pressure of the liquefied natural gas from the inner layer to the concrete wall, thus requiring a certain load-bearing capacity. The insulation space of the insulation layer, from the inner layer (inner membrane) to the outer layer (moisture barrier), is completely sealed and permanently placed within the liquefied natural gas layer for easy monitoring.

[0046] Step 140: A process operation platform is set on the top of the cavern in the abandoned shaft, and a pump pit for installing a submersible pump is set below the process operation platform.

[0047] Among them, the top of the abandoned shaft and tunnel is equipped with a process operation platform for the installation and maintenance of equipment such as valves and instruments entering the tunnel. Below the operation platform is a pump pit for installing equipment such as submersible pumps. This pump pit is a vertical shaft pump pit.

[0048] In some embodiments, the process operation platform and the tank wall structure of the pump pit that contacts liquefied natural gas are both composite tank wall structures composed of a stainless steel membrane and the insulation layer.

[0049] To prevent liquefied natural gas (LNG) leakage, all fluid inlet and outlet pipelines and instrument connections within the storage facility are connected from the top of the tank. The converted cryogenic LNG storage facility in the abandoned mine shaft is equipped with at least one feed pipe, which is inserted into the storage facility via a vertical feed pipe. The operator can adjust the LNG feed rate by manipulating the feed valve at the top of the storage facility. The LNG storage tank is connected to other pipelines within the station via a vapor phase pipeline to transport the vaporized gas generated within the storage facility and the gas generated by the station's surface system to the venting system. No gas is emitted during normal operation.

[0050] For example, refer to the appendix. Figure 7 As shown, in this embodiment, the original shaft is excavated, and an operating platform (including a lining structure with a lining thickness of 350 mm) measuring 4.0 meters (length) × 4.0 meters (width) × 2.7 meters (height) is constructed for the installation and maintenance of equipment such as valves and instruments entering the tunnel. A pump pit can be set below the operating platform for installing equipment such as submersible pumps. For ease of later testing, a pump cylinder size of DN500 is recommended, and the pump pit size is recommended to be 1200 mm × 1200 mm × 500 mm.

[0051] Step 150: Deploy groundwater control units around the reservoir to drain fissure water in the rock mass during construction and to restore rock mass saturation to form a cryosphere during operation.

[0052] In some implementations, the groundwater control unit includes an upper water replenishment subunit and a lower drainage subunit.

[0053] In some embodiments, the deployment of groundwater control units around the reservoir includes: arranging the water supply holes of the upper water supply subunit and the drainage holes of the lower drainage subunit in a ring within a predetermined distance range around the cavern of the reservoir.

[0054] One purpose of the groundwater control unit in this application embodiment is to drain the fissure water in the rock mass during the construction period and before the formation of the cryosphere, so that the bedrock fissure water is in an unsaturated state, avoiding water pressure on the sealing system inside the tank, and also creating a dry environment for the construction of the sealing system. During the concrete pouring stage, the main function of the groundwater control unit is to reduce the amount of water flowing into the storage tank; during the installation of the sealing system, the function of the drainage system is to reduce humidity; during the initial cooling period in operation, the function of the drainage system is to drain the rock mass and reduce the saturation of rock fissures; after the rock mass has dried to a certain extent at low temperature, the function of the drainage system is to restore the rock mass to saturation and form a cryosphere.

[0055] The primary purpose of setting up a groundwater control unit is to drain fissure water in the bedrock during construction and before the formation of the cryosphere, ensuring the bedrock fissure water remains unsaturated and preventing water pressure on the sealing system inside the tank. It also creates a dry environment for the sealing system construction. During the concrete pouring stage, the groundwater control unit's functions include, but are not limited to, reducing the amount of water flowing into the storage tank; during the sealing system installation, the drainage system's functions include, but are not limited to, reducing humidity; during the initial cooling period in operation, the drainage system's functions include, but are not limited to, draining the bedrock and reducing the saturation of rock fissures; and after the bedrock has dried to a certain extent at low temperatures, the drainage system's functions include, but are not limited to, restoring the bedrock to saturation and preventing the formation of a cryosphere.

[0056] For example, in this embodiment, the water replenishment subunit and the drainage subunit each have four water replenishment and drainage holes within a range of 5 meters above and 5 meters below the cavern, respectively. The holes are spaced 5 meters apart, have a diameter of 110 mm, and an overlap length of 1 meter. During the conversion of abandoned mine shafts into cryogenic liquefied natural gas (LNG) systems, the water replenishment and drainage holes function as drainage holes, drawing water from the groundwater level around the cavern to facilitate on-site construction. During the trial operation of cryogenic LNG in abandoned mine shafts, the water replenishment and drainage holes are connected to the water replenishment pipeline in the main tunnel to replenish water, gradually achieving water saturation of the rock mass and facilitating the formation of the freeze zone.

[0057] To provide a complete set of technologies and solutions for the construction of cryogenic liquefied natural gas (LNG) storage facilities by converting abandoned mine shafts and tunnels, and to promote the long-term, large-scale storage of natural gas and LNG and ensure energy security, this application, based on the construction principles and functional requirements of cryogenic liquid storage, takes a practical engineering approach. It covers everything from the selection of main roadway locations, shaft and tunnel modification structures, and support schemes for the conversion of abandoned mine shafts and tunnels into cryogenic LNG storage facilities, to the functional design of different individual units such as the tank wall structure of the cryogenic LNG storage facility, and to the system solutions for groundwater control units and other auxiliary facilities. Only moderately strong hard rock strata are needed to meet all construction requirements. It has extremely high tolerance for geological conditions and is applicable to various scenarios with different engineering geology, hydrogeology, and underground engineering layouts. By integrating various underground units, structures, and devices, this method provides a large-scale, highly targeted, highly reliable, easy-to-operate, low-cost, and widely applicable approach for the construction of cryogenic liquefied natural gas (LNG) storage facilities in abandoned mine shafts. It can be quickly applied to the construction of the natural gas storage and LNG industry chain, effectively reducing the storage costs of natural gas and LNG, improving economic efficiency, and thus promoting the healthy development of the gas storage and abandoned underground space utilization industry chain.

[0058] This application embodiment effectively utilizes existing geological conditions to reduce the risk of LNG storage construction by selecting abandoned shafts with acceptable surrounding rock stability and constructing a double airtight barrier, ensuring long-term structural stability and operational safety. Simultaneously, the dual sealing design of stainless steel membrane and cryosphere significantly improves the leak-proof performance of LNG storage. By modifying the cross-section of the abandoned shaft into a pre-defined trapezoidal structure to accommodate the installation of the stainless steel membrane, precise deployment and sealing integrity of the membrane material are ensured. The support unit integrates the self-stabilizing capacity of the surrounding rock with reinforcement measures, strengthening the cavern structure support, preventing the risk of collapse during construction, and ensuring operational safety. Furthermore, by laying a composite tank wall structure on the inner surface of the tunnel, utilizing stainless steel... The synergistic effect of the membrane and insulation layer achieves efficient thermal insulation to reduce liquefied natural gas evaporation loss. The dual airtight barrier mechanism enhances the overall sealing performance and optimizes the thermal efficiency and operational reliability of the low-temperature storage environment. The process operation platform set up at the top of the cavern facilitates equipment installation and maintenance, improving maintenance convenience. The design of the pump pit below supports the stable installation of submersible pumps, ensuring the continuity and operational efficiency of the liquefied natural gas transportation process. By deploying groundwater control units to drain fissure water during construction to create a dry construction environment, water pressure interference is reduced. During operation, the rock mass is restored to saturation to form a cryosphere, and the natural freezing barrier enhances the sealing effect, reducing the need for long-term maintenance.

[0059] This application also discloses a system for converting abandoned mine shafts into liquefied natural gas storage facilities. (See attached document.) Figure 8 As shown, the system includes: a double barrier construction module 1010, a tunnel cross-section modification module 1020, a tunnel surface paving module 1030, an operation platform and pump pit construction module 1040, and a water control unit deployment module 1050.

[0060] The dual barrier construction module 1010 is used to select abandoned shafts and tunnels with acceptable surrounding rock stability and construct dual airtight barriers.

[0061] The tunnel section modification module 1020 is used to modify the cross-section of the abandoned tunnel into a trapezoidal structure with a preset angle to adapt to the installation requirements of the stainless steel membrane material. Based on the anchor bolts, concrete lining layer, surrounding rock and the modified cross-section, a support unit is constructed to ensure the stability of the tunnel structure and construction safety.

[0062] The tunnel surface paving module 1030 is used to lay a composite tank wall structure consisting of a stainless steel membrane and an insulation layer on the inner surface of the tunnel in the abandoned mine tunnel, so as to provide insulation and double airtight barrier functions and ensure the sealing and thermal efficiency of cryogenic liquefied natural gas storage.

[0063] The operating platform and pump pit construction module 1040 is used to set up a process operating platform on the top of the cavern in the abandoned shaft, and to set up a pump pit for installing a submersible pump below the process operating platform.

[0064] The water control unit deployment module 1050 is used to deploy groundwater control units around the reservoir to drain fissure water in the rock mass during construction and to restore rock mass saturation to form a cryosphere during operation.

[0065] In some embodiments, the system further includes: an integrated tank wall structure comprising, from the inside out, the stainless steel membrane, the insulation layer, the reinforced concrete lining layer, and the surrounding rock; and a gas phase pipeline and a feed pipe for connecting to the storage tank.

[0066] For example, to prevent liquefied natural gas (LNG) leaks, all fluid inlet and outlet pipelines and all instrument connections within the storage facility are connected from the top of the tank. A converted cryogenic LNG storage facility from abandoned mine shafts is equipped with at least one feed pipe, with feeding achieved through a vertical feed pipe inserted into the storage facility. Operators can adjust the LNG feed rate by manipulating the feed valve at the top of the storage facility. The LNG storage tank is connected to other pipelines within the station via a vapor phase pipeline to transport the vaporized gas generated within the storage facility and the gas generated by the station's surface system to the venting system. No gas emissions occur during normal operation, and a pump pit is provided below the operating platform for installing equipment such as submersible pumps.

[0067] This application addresses the current situation where there are no precedents for constructing cryogenic liquefied natural gas (LNG) storage facilities by converting abandoned mine shafts, and existing storage technologies mainly focus on surface membrane tanks, salt cavern storage facilities, and depleted gas reservoir storage facilities. Surface membrane tanks are costly and small in scale, while salt cavern and depleted gas reservoir storage facilities are significantly limited by geological structure, geographical resources, and location, making it difficult to meet the needs of large-scale underground gas storage construction in severely gas-deficient areas. This application creates a system based on converting abandoned mine shafts into LNG storage facilities, offering significant advantages in both time and spatial scales, and representing the optimal approach for long-term, large-scale gas storage. This application is of great significance; it solves the problems of small scale, high cost, and significant limitations due to geological conditions and geographical location in existing gas storage and cryogenic liquefied natural gas (LNG) storage methods. It provides a comprehensive solution, from the selection of main roadway sites, roadway modification structures, and support schemes for converting abandoned shafts into cryogenic LNG storage facilities, to the functional design of different individual units such as the tank wall structure of the cryogenic LNG storage facility, and auxiliary facilities such as groundwater control units. All construction requirements can be met by selecting underground spaces in abandoned shafts of moderate strength, demonstrating extremely high tolerance for geological conditions and a wide range of applicability. The abandoned shafts in this application... The tank wall structure of the cryogenic liquefied natural gas (LNG) storage facility, from the inside out, consists of a stainless steel membrane, an insulation layer, a reinforced concrete lining layer, and surrounding rock, which together form the sealing and force transmission structure of the cryogenic LNG cavern. The pressure of the LNG is mainly borne by the reinforced concrete lining layer and the surrounding rock. Simultaneously, two airtight barriers, a stainless steel membrane and a cryosphere, are installed, effectively solving the cavern sealing and stability problems under efficient operation of the cryogenic LNG storage facility. The device parameters can be appropriately adjusted according to actual operating conditions, offering significant optimization potential. The construction device for converting abandoned shafts into cryogenic LNG storage facilities according to this application embodiment not only... It can be applied to liquefied natural gas storage and also to the utilization of abandoned underground spaces, which is of great value for natural gas storage, comprehensive utilization of underground spaces and energy structure transformation. The embodiments of this application have the advantages of large scale, strong targeting, high reliability, convenient operation, low cost and wide applicability through the comprehensive application of various underground structures, units and materials. It can be quickly applied to the construction of liquefied natural gas storage facilities and comprehensive utilization of abandoned underground spaces, effectively reducing the storage cost of gas storage and cryogenic liquefied natural gas, improving the economic benefits of storage construction, and thus promoting the healthy development of the gas storage and comprehensive utilization of underground spaces industry chain.

[0068] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this application, and this application is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and substance of this application, and these modifications and improvements are also considered to be within the scope of protection of this application.

Claims

1. A method for converting abandoned mine shafts into liquefied natural gas storage facilities, characterized in that, include: Select abandoned shafts and tunnels with acceptable surrounding rock stability and construct double airtight barriers; The cross-section of the abandoned shaft is transformed into a trapezoidal structure with a preset angle to accommodate the installation requirements of the stainless steel membrane material, and a support unit is constructed based on the anchor bolts, concrete lining layer, surrounding rock, and the transformed cross-section. A composite tank wall structure consisting of a stainless steel membrane and an insulation layer is laid on the inner surface of the abandoned shaft tunnel. A process operation platform is set on the top of the cavern in the abandoned shaft, and a pump pit for installing a submersible pump is set below the process operation platform. Groundwater control units are deployed around the reservoir to drain fissure water in the rock mass during construction and to restore rock mass saturation to form a cryosphere during operation.

2. The method according to claim 1, characterized in that, The dual airtight barrier includes a first barrier and a second barrier, and the construction of the dual airtight barrier includes: The first barrier is constructed as a stainless steel membrane, and the second barrier is constructed as a cryosphere formed by frozen groundwater; An insulation layer, a waterproof layer, and a concrete lining layer are provided between the first barrier layer and the second barrier layer.

3. The method according to claim 2, characterized in that, The method further includes: A pleated structure is provided on the surface of the stainless steel film, and the pleat spacing of the pleated structure is 400-700 mm.

4. The method according to claim 1, wherein the abandoned shaft with satisfactory surrounding rock stability is a main shaft with a gentle slope, characterized in that, The process of transforming the cross-section of the abandoned shaft into a trapezoidal structure with a preset angle includes: The weak support areas of the abandoned tunnel are reinforced with anchor bolts and grouting. The anchor bolt holes and grouting holes are arranged at a preset interval and the depth of the anchor bolt holes and grouting holes is greater than the size of the tunnel structure. The abandoned shaft was lined with reinforced concrete to form the concrete lining layer.

5. The method according to claim 4, characterized in that, The slope of the gentle slope roadway shall not exceed 5%, the corner angles of the trapezoidal structure shall be limited to 90° and 135°, the length of the anchor bolt shall be 2.5 meters, the spacing between the anchor bolts shall be 1.5 meters × 1.5 meters, and the thickness of the concrete lining layer shall not be less than 100 millimeters.

6. The method according to claim 1, wherein the insulation layer is composed of plywood, polyurethane foam, elastic sealant, and a moisture-proof layer from the inside out, characterized in that, The method further includes: The moisture-proof layer is applied to the concrete wall to prevent water vapor penetration.

7. The method according to claim 1, wherein the groundwater control unit comprises an upper water replenishment subunit and a lower drainage subunit, characterized in that, The deployment of groundwater control units around the storage facility includes: The water supply holes of the upper water supply subunit and the drainage holes of the lower drainage subunit are arranged in a ring within a predetermined distance range around the cavern of the storage tank.

8. The method according to claim 1, characterized in that, The process operation platform and the tank wall structure of the pump pit that are in contact with liquefied natural gas are both composite tank wall structures composed of a stainless steel membrane and the insulation layer.

9. A system for converting abandoned mine shafts into liquefied natural gas storage facilities, characterized in that, include: The dual-barrier construction module is used to select abandoned shafts and tunnels with acceptable surrounding rock stability and construct dual airtight barriers. The shaft and tunnel cross-section modification module is used to modify the cross-section of the abandoned shaft and tunnel into a trapezoidal structure with a preset angle, to adapt to the installation requirements of the stainless steel membrane material, and to construct a support unit based on anchor bolts, concrete lining layer, surrounding rock and the modified cross-section. A roadway surface paving module is used to pave a composite tank wall structure consisting of a stainless steel membrane and an insulation layer on the inner surface of the roadway in the abandoned mine tunnel. The operating platform and pump pit construction module is used to set up a process operating platform on the top of the cavern in the abandoned shaft, and to set up a pump pit for installing a submersible pump below the process operating platform. The water control unit deployment module is used to deploy groundwater control units around the reservoir, which are used to drain the fissure water in the rock mass during the construction period and to restore the rock mass to saturation during the operation period to form a cryosphere.

10. The system based on the conversion of abandoned shafts into liquefied natural gas storage facilities according to claim 9, characterized in that, The system also includes: The integrated tank wall structure includes, from the inside out, the stainless steel membrane, the insulation layer, the reinforced concrete lining layer, and the surrounding rock; Vapor phase pipeline and feed pipe are used to connect to the storage tank.

Images