Gas injection residual heat efficient recycling system for gas storage

Abstract

The application belongs to the field of oil and gas field ground engineering, and discloses a kind of gas storage injection gas waste heat efficient recycling system. Through the use of endothermic and exothermic characteristics in the process of hydrate salt generation and decomposition, the natural gas in the gas injection process of gas storage is rapidly cooled, and its waste heat is efficiently recycled, long-time stored, and the heat is utilized across seasons. The technology efficiently recycles the waste heat generated in the gas injection process of gas storage through the waste heat recovery system, and is flexibly applied to other process, to realize comprehensive utilization of energy and energy saving and consumption reduction.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field surface engineering, specifically relating to a highly automated gas storage storage gas injection waste heat recovery and utilization system. Background Technology

[0002] Gas storage facilities are a critical infrastructure element in the natural gas industry, primarily functioning to store and regulate natural gas supply to cope with demand fluctuations. Underground gas storage facilities, due to their large capacity, economic efficiency, and safety, can effectively balance the uneven supply and demand of natural gas. The operating cycle of a gas storage facility is typically one year, with gas extraction in winter and spring and gas injection in summer and autumn. During injection, natural gas undergoes two or three stages of compression, resulting in a significant temperature increase, necessitating cooling methods to ensure system safety and efficiency. However, existing air-cooled systems cannot recover waste heat.

[0003] During the natural gas injection process into a gas storage facility, a compressor is used to compress the natural gas, generating a significant amount of heat. Current technologies have significant shortcomings in waste heat utilization, primarily because the heat is simply dissipated or treated by traditional cooling equipment. This not only wastes a large amount of energy but also increases energy costs. Furthermore, most of the waste heat generated in gas storage facilities is not effectively stored and utilized, failing to provide additional energy support when needed. With increasing global energy demand and higher requirements for energy efficiency, maximizing the recovery and utilization of waste heat generated during gas injection has become an urgent problem. Achieving efficient waste heat recovery and utilization can not only reduce energy waste, decrease dependence on external energy sources, and lower energy costs, but also have a positive impact on environmental protection. Currently, although research has proposed the concept of waste heat recovery, most solutions remain in the theoretical stage or face challenges such as high cost and low efficiency in practical applications. Therefore, a new technological solution is urgently needed to effectively recover and utilize waste heat during the gas injection process in gas storage facilities, thereby improving overall energy efficiency, reducing energy consumption, and promoting sustainable development.

[0004] Research on the rational recovery of waste heat using thermochemical particulate heat exchange technology has broad prospects. With the increasing demand for energy efficiency and environmental protection, particulate heat exchange technology is attracting more and more attention from researchers. In the field of energy storage research, solid particles are used as heat storage media to improve heat storage and release efficiency. The development of particulate waste heat recovery technology has matured. Gravity-driven moving bed heat exchangers are currently widely used in solid slag waste heat recovery. Compared with traditional heat exchange technologies, gravity-driven moving bed heat exchanger systems are simpler. Within the moving bed, there are currently two main heat exchange methods: one is direct heat exchange between air and particles within the moving bed; the other is heat exchange between particles and heat exchange tubes, where the fluid can be water or air. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a high-efficiency waste heat recovery and utilization system for gas storage injection. By utilizing the endothermic and exothermic characteristics of the formation and decomposition of hydrated salts, it achieves rapid cooling of natural gas during the gas injection process, while simultaneously recovering and storing the waste heat efficiently over long periods, enabling cross-seasonal utilization of heat. This technology efficiently recovers the waste heat generated during the gas injection process and flexibly applies it to other processes to achieve comprehensive energy utilization and energy conservation.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: a high-efficiency waste heat recovery and utilization system for gas injection in a gas storage facility, comprising: a moving bed heat exchanger a, connected to a reheater via a flexible screw feeder; the top of the reheater connected to a high hydration salt sealed storage tank; the bottom of the reheater connected to a low hydration salt sealed storage tank via a flexible screw feeder; the high hydration salt sealed storage tank and the low hydration salt sealed storage tank connected to the moving bed heat exchanger b via a flexible screw feeder; wherein the moving bed heat exchanger a cools the natural gas, and the moving bed heat exchanger b heats the natural gas.

[0007] Furthermore, the moving bed heat exchanger a has a high-temperature dehydrated particle outlet at the bottom and a spirally rising pipeline inside. A high-temperature natural gas inlet a is provided at the lower end of the pipeline, and a low-temperature natural gas outlet a is provided at the upper end of the pipeline. The moving bed heat exchanger a also has a reheated hydrate particle inlet on its side and a hydrated salt particle inlet a at its top. The hydrated salt particle inlet a is connected to a high hydrated salt sealed storage tank by a pipeline. The reheated hydrate particle inlet is connected to the bottom of the reheater through a flexible screw feeder, and the high-temperature dehydrated particle outlet is connected to the top of the reheater through a flexible screw feeder.

[0008] Furthermore, the moving bed heat exchanger a is provided with a steam outlet at the top.

[0009] Furthermore, the reheater is provided with a hydrated salt particle inlet b at the top, and the hydrated salt particle inlet b is connected by a pipeline to a high hydrated salt sealed storage tank.

[0010] Furthermore, the contents of the high-hydrated salt sealed storage tank are a mixture of MgSO4·7H2O and CaCl2·6H2O.

[0011] Furthermore, the contents of the low-hydrate salt sealed storage tank are a mixture of MgSO4·2H2O and CaCl2·2H2O.

[0012] Furthermore, the moving bed heat exchanger b has a low-temperature dehydrated particle inlet at the top, which is connected to a low-hydration salt sealed storage tank via a flexible screw feeder; the moving bed heat exchanger b also has a hydrated salt particle outlet at the top, which is connected to a high-hydration salt sealed storage tank via a flexible screw feeder; the moving bed heat exchanger b has a spirally rising pipeline inside, with a low-temperature natural gas inlet b extending from the lower side pipeline end and a high-temperature natural gas outlet b extending from the upper side pipeline end.

[0013] Furthermore, the moving bed heat exchanger b is provided with a dry air outlet at the bottom and a humid air inlet at the top, and a pipeline is provided from the dry air outlet to the humid air inlet, with a steam generator installed on the pipeline.

[0014] Another objective of this invention is to protect the recovery and utilization method of the above-mentioned gas storage tank gas injection waste heat recovery and utilization system. Specifically, the method involves: on one side, high-temperature natural gas enters and low-temperature natural gas exits in the moving bed heat exchanger a, and the released heat is discharged to the reheater for storage through high-temperature dehydration particles. The heat in the reheater is used to absorb and dehydrate the mixture of MgSO4·7H2O and CaCl2·6H2O in the high-hydration salt sealed storage tank to form a mixture of MgSO4·2H2O and CaCl2·2H2O in the low-hydration salt sealed storage tank. Simultaneously, on the other side, the mixture of MgSO4·2H2O and CaCl2·2H2O in the low-hydration salt sealed storage tank combines with water in the moving bed heat exchanger b to form a mixture of MgSO4·7H2O and CaCl2·6H2O in the high-hydration salt sealed storage tank and releases heat, which is absorbed when low-temperature natural gas enters and high-temperature natural gas exits in the moving bed heat exchanger b. The H2O in the moving bed heat exchanger b is generated by a steam generator through circulation.

[0015] The advantages of this invention compared to the prior art are:

[0016] This invention achieves efficient recovery, storage, and utilization of waste heat during natural gas injection by integrating a screw feeder with various devices, significantly improving energy efficiency and reducing energy waste. Compared to traditional air coolers, this technology reduces floor space and investment costs, while its highly efficient heat recovery characteristics significantly reduce operating costs. By efficiently recovering waste heat, CO2 emissions are reduced, making a positive contribution to mitigating global warming. This technology supports long-term storage and cross-seasonal or cross-distance utilization of natural gas waste heat, improving the flexibility and adaptability of gas storage facilities, enabling them to adapt to different operating conditions and needs, and achieving more flexible operation and management.

[0017] This invention employs a spiral flexible feeder to transport the thermochemical adsorption heat storage medium between the moving bed, large storage tank, small storage tank, and well site, saving labor costs. The reheat system used in this solution preheats a portion of the particles sent to the moving bed heat exchanger, further improving heat utilization efficiency. Furthermore, the flexible feeder allows for particle circulation and heat exchange within the system. The flexible feeder precisely controls the particle flow rate and velocity, contributing to uniform particle distribution within the heat exchange device, reducing particle accumulation and agglomeration, improving system stability, ensuring continuous particle circulation, and thus guaranteeing the stability and reliability of the heat exchange process.

[0018] Preliminary calculations show that the thermal storage cost of this technical solution is only 1.3% of that of traditional thermal storage media such as paraffin. Taking a gas storage facility with an annual injection capacity of 1.5 billion standard cubic meters as an example, the total residual heat is approximately 90 million kWh. Considering fluctuations in its operating conditions, the theoretically recoverable residual heat is approximately 74 million kWh, the effectively recoverable residual heat is 59.2 million kWh (calculated based on a residual heat recovery rate of 80%), and the effectively usable residual heat is 47 million kWh (calculated based on a residual heat utilization rate of 80%). If 80% of the effectively usable residual heat replaces natural gas heating and 20% replaces electric heating, the annual revenue would be 11.7 million yuan (calculated based on a natural gas price of 1.68 yuan / standard cubic meter and an electricity price of 0.52 yuan / kWh), while also reducing CO2 emissions by approximately 17,300 tons annually. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a schematic diagram of the structure of the waste heat recovery and utilization system for gas injection in the gas storage facility according to the present invention.

[0021] In the diagram: 1. High-temperature natural gas inlet a; 2. Low-temperature natural gas outlet a; 3. Moving bed heat exchanger a; 41. Hydrated salt particle inlet a; 42. Hydrated salt particle inlet b; 5. Reheated hydrated salt particle inlet; 6. High-temperature dehydrated particle outlet; 7. Steam outlet; 8. Flexible screw feeder; 9. Reheater; 101. Low-hydrated salt sealed storage tank; 102. High-hydrated salt sealed storage tank; 11. Moving bed heat exchanger b; 12. Low-temperature dehydrated particle inlet; 13. Hydrated salt particle outlet; 14. Humid air inlet; 15. Dry air outlet; 16. Low-temperature natural gas inlet b; 17. High-temperature natural gas outlet b; 18. Steam generator. Detailed Implementation

[0022] The present invention is described in detail below through specific embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can all be obtained commercially. Example

[0023] A high-efficiency waste heat recovery and utilization system for gas injection in a gas storage facility includes: a moving bed heat exchanger a3 connected to a reheater 9 via a flexible screw feeder 8; the top of the reheater 9 connected to a high-hydration-salt sealed storage tank 102, and the bottom of the reheater 9 connected to a low-hydration-salt sealed storage tank 101 via the flexible screw feeder 8; the high-hydration-salt sealed storage tank 102 and the low-hydration-salt sealed storage tank 101 are connected to a moving bed heat exchanger b11 via the flexible screw feeder 8; wherein the moving bed heat exchanger a3 cools the natural gas. A moving bed heat exchanger b11 heats natural gas; the moving bed heat exchanger a3 has a spirally rising pipeline inside, with a high-temperature natural gas inlet a1 extending from the lower end of the pipeline and a low-temperature natural gas outlet a2 extending from the upper end of the pipeline; the bottom of the moving bed heat exchanger a3 has a high-temperature dehydration particle outlet 6, the side of the moving bed heat exchanger a3 also has a reheat hydrate particle inlet 5, and the top of the moving bed heat exchanger a3 also has a hydrated salt particle inlet a41, which has a pipe. The reheater 9 is connected to a high-hydrate salt sealed storage tank 102 via a pipeline. The reheated hydrate particle inlet 5 is connected to the bottom of the reheater 9 via a flexible screw feeder 8, and the high-temperature dehydrated particle outlet 6 is connected to the top of the reheater 9 via the flexible screw feeder 8. The moving bed heat exchanger a3 has a steam outlet 7 at its top. The reheater 9 has a hydrated salt particle inlet b42 at its top, which is connected to the high-hydrate salt sealed storage tank 102 via a pipeline. The moving bed heat exchanger b11 has spirally rising pipes inside. The moving bed heat exchanger b11 has a low-temperature natural gas inlet b16 extending from the lower side and a high-temperature natural gas outlet b17 extending from the upper side. The moving bed heat exchanger b11 has a low-temperature dehydrated particle inlet 12 at the top, which is connected to the low-hydration salt sealed storage tank 101 via a flexible screw feeder 8. The moving bed heat exchanger b11 also has a hydrated salt particle outlet 13 at the top, which is connected to the high-hydration salt sealed storage tank 102 via a flexible screw feeder 8.

[0024] The high-hydrate salt sealed storage tank 102 contains a mixture of MgSO4·7H2O and CaCl2·6H2O.

[0025] The low-hydrate salt sealed storage tank 101 contains a mixture of MgSO4·2H2O and CaCl2·2H2O.

[0026] This invention aims to provide a thermochemical energy storage system that utilizes the endothermic properties of the decomposition process of thermochemical granular hydrated salts to absorb waste heat and recover the heat in the form of solid particles. The system employs chemical reactions that can absorb or release heat energy to achieve heat storage and regulation. It has three operational stages: endothermic dissociation → storage of reaction products → exothermic reaction of dissociation products. Considering the temperature of compressed natural gas is between 60 and 100 °C, and the differences in the reaction temperature ranges of different heat-absorbing hydrous salts (e.g., MgSO4·7H2O dehydrates to MgSO4·6H2O at 30-45 °C with an endothermic enthalpy of 100 J / g; MgSO4·6H2O dehydrates to MgSO4·2H2O at 60-100 °C with an endothermic enthalpy of 1000 J / g; CaCl2·6H2O dehydrates to CaCl2·2H2O at 30-100 °C with an endothermic enthalpy of 1450 J / g), in order to achieve full recovery of waste heat and avoid waste of waste heat in the low-temperature section, this patent selects a mixture of MgSO4·7H2O and CaCl2·6H2O as the heat-absorbing hydrous salt (the cost required to absorb the same amount of heat is only 1% of that of paraffin). In addition, by mixing MgSO4·7H2O with CaCl2·6H2O, problems such as the easy deliquescence of CaCl2·6H2O can be avoided.

[0027] During the thermal storage process, high-temperature natural gas undergoes countercurrent heat exchange with MgSO4·7H2O and CaCl2·6H2O in a moving bed. MgSO4·7H2O and CaCl2·6H2O absorb heat during the heating process, transforming into MgSO4·2H2O and CaCl2·2H2O respectively. Subsequently, this heat is stored in sealed tanks suitable for transportation and handling, facilitating flexible utilization of the heat across seasons and distances.

[0028] In the waste heat utilization process, a mixture of MgSO4·2H2O and CaCl2·2H2O is contacted with water vapor to generate MgSO4·7H2O and CaCl2·6H2O, releasing a large amount of heat (55~70℃, approximately 1200 J / g). During storage, MgSO4·2H2O and CaCl2·2H2O are placed in a sealed storage tank, allowing for flexible utilization of the stored heat across different seasons or distances.

[0029] During summer gas injection, the high-temperature natural gas is exchanged with hydrated salt particles (a mixture of MgSO4·7H2O and CaCl2·6H2O) in a moving bed heat exchanger. This process cools the natural gas while simultaneously desorbing MgSO4·7H2O and CaCl2·6H2O into MgSO4·2H2O and CaCl2·2H2O, storing the heat as chemical energy. Furthermore, to improve waste heat recovery efficiency, the desorbed high-temperature MgSO4·2H2O and CaCl2·2H2O are used in reheater 9 to heat a portion of the low-temperature MgSO4·7H2O and CaCl2·6H2O. The reheated hydrated salt is then passed into moving bed heat exchanger a3 for further heat exchange. The dehydrated particles are then stored in a sealed tank for subsequent cross-seasonal and cross-distance utilization.

[0030] The dehydrated granules are then stored in sealed tanks. A continuous storage and intermittent transportation system for granules is constructed, consisting of a large storage tank, a flexible screw feeder, and container-type small storage tanks. The dehydrated granules are transported to the large storage tank by the flexible screw feeder 8, enabling continuous operation of the system. Once the storage tank is full, the dehydrated granules are loaded into container tanks on large trucks by the flexible screw feeder 8 and transported to the well site for waste heat utilization.

[0031] During the waste heat utilization process in winter, air is drawn in through steam generator 18 and mixed with atomized water to create humid air. This humid air, along with a mixture of MgSO4·2H2O and CaCl2·2H2O, enters the moving bed heat exchanger b11 from the top. The MgSO4·2H2O and CaCl2·2H2O contact with the humid air to generate MgSO4·7H2O and CaCl2·6H2O, releasing a large amount of heat (55~70℃, approximately 1200 J / g). This heat exchange occurs counter-currently with the low-temperature natural gas entering from the bottom, heating the natural gas to a high temperature before it leaves the moving bed heat exchanger. The dry air exits from the bottom of the moving bed heat exchanger b11 and returns to the steam generator 18, circulating for reuse to improve thermal energy utilization.

[0032] The entire system utilizes a flexible screw feeder for particle transport, achieving a high degree of automation. This not only significantly reduces labor costs but also precisely controls particle flow and velocity, helping to achieve uniform particle distribution in the heat exchanger, reducing particle accumulation and agglomeration, improving system stability, ensuring continuous particle circulation, and enhancing heat exchange efficiency.

[0033] When the gas storage and injection station cannot fully absorb the waste heat recovered in summer during winter, the recovered waste heat can be transported to surrounding well sites for cross-distance utilization during the summer gas storage process. The process is as follows: Figure 1As shown in the diagram, a continuous storage and intermittent transport system for granules was constructed, consisting of a large storage tank, a flexible screw feeder, and containerized small storage tanks. The flexible screw feeder transports the dehydrated granules to the large storage tank for storage, enabling continuous system operation. Once the tank is full, the flexible screw feeder loads the dehydrated granules into containerized storage tanks on large trucks for transport to the well site for waste heat utilization. This achieves continuous recovery of waste heat within the gas storage facility and intermittent transport of granules between the storage facility and the well site, significantly reducing the labor costs required for waste heat recovery, storage, and long-distance utilization.

[0034] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A high-efficiency waste heat recovery and utilization system for gas injection in a gas storage facility, characterized in that, include: The moving bed heat exchanger a (3) is connected to the reheater (9) via a flexible screw feeder (8). The top of the reheater (9) is connected to the high hydrate salt sealed storage tank (102), and the bottom of the reheater (9) is connected to the low hydrate salt sealed storage tank (101) via a flexible screw feeder (8). The high hydrate salt sealed storage tank (102) and the low hydrate salt sealed storage tank (101) are connected to the moving bed heat exchanger b (11) via a flexible screw feeder (8). The moving bed heat exchanger a (3) cools the natural gas, and the moving bed heat exchanger b (11) heats the natural gas. The moving bed heat exchanger a (3) has a spiral rising pipeline inside, and a high-temperature natural gas inlet is provided at the lower side pipeline end. A low-temperature natural gas outlet a(2) is provided at the end of the upper side pipe of the moving bed heat exchanger a(3); a high-temperature dehydrated particle outlet (6) is provided at the bottom of the moving bed heat exchanger a(3), a reheated hydrate particle inlet (5) is also provided on the side of the moving bed heat exchanger a(3), and a hydrated salt particle inlet a(41) is also provided at the top of the moving bed heat exchanger a(3). The hydrated salt particle inlet a(41) is connected to a high hydrated salt sealed storage tank (102) by a pipeline. The reheated hydrate particle inlet (5) is connected to the bottom of the reheater (9) through a flexible screw feeder (8), and the high-temperature dehydrated particle outlet (6) is connected to the top of the reheater (9) through a flexible screw feeder (8). The top of the reheater (9) is provided with a steam outlet (7); the top of the reheater (9) is provided with a hydrated salt particle inlet b (42), which is connected to a high hydrated salt sealed storage tank (102) by a pipeline; the high hydrated salt sealed storage tank (102) contains a mixture of MgSO4·7H2O and CaCl2·6H2O; the low hydrated salt sealed storage tank (101) contains a mixture of MgSO4·2H2O and CaCl2·2H2O; the moving bed heat exchanger b (11) has a spiral rising pipeline inside, with a low temperature natural gas inlet b (16) extending out from the lower side pipeline end and a high temperature natural gas outlet extending out from the upper side pipeline end. b (17); The moving bed heat exchanger b (11) is provided with a low temperature dehydration particle inlet (12) at the top, and the low temperature dehydration particle inlet (12) is connected to the low hydration salt sealed storage tank (101) through a flexible screw feeder (8); The moving bed heat exchanger b (11) is provided with a hydrated salt particle outlet (13) at the top, and the hydrated salt particle outlet (13) is connected to the high hydration salt sealed storage tank (102) through a flexible screw feeder (8); The moving bed heat exchanger b (11) is provided with a dry air outlet (15) at the bottom and a wet air inlet (14) at the top, and a pipeline is provided from the dry air outlet (15) to the wet air inlet (14), and a steam generator (18) is provided on the pipeline.

2. The method for recycling waste heat from gas injection in a gas storage facility as described in claim 1, characterized in that, The specific steps are as follows: On one side, high-temperature natural gas enters the moving bed heat exchanger a (3), and low-temperature natural gas is discharged. The released heat is discharged to the reheater (9) through high-temperature dehydration particles for storage. The heat in the reheater (9) is used to absorb and dehydrate the mixture of MgSO4·7H2O and CaCl2·6H2O in the high-hydration salt sealed storage tank (102) into a mixture of MgSO4·2H2O and CaCl2·2H2O in the low-hydration salt sealed storage tank (101); at the same time, on the other side, the low-hydration salt... The mixture of MgSO4·2H2O and CaCl2·2H2O in the salt-sealed storage tank (101) combines with water in the moving bed heat exchanger b (11) to form a mixture of MgSO4·7H2O and CaCl2·6H2O in the high-hydration salt-sealed storage tank (102) and releases heat, which is used to allow low-temperature natural gas to enter the moving bed heat exchanger b (11) and absorb the high-temperature natural gas when it is discharged. The H2O in the moving bed heat exchanger b (11) is generated by the steam generator (18) through circulation.

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