A distributed natural gas recovery system and method based on step-by-step utilization of liquid nitrogen cold energy

Abstract

This invention relates to a decentralized gas field natural gas recovery system and method based on the cascade utilization of liquid nitrogen cold energy. In this natural gas recovery system, a pretreatment skid-mounted module includes a precooling device, a first gas-liquid separation device, and an adsorption tower. The precooling device performs preliminary precooling on the recovered natural gas, the first gas-liquid separation device performs gas-liquid separation on the recovered natural gas, and the adsorption tower performs drying and carbon removal on the natural gas. A cryogenic liquefaction skid-mounted module includes a precooling heat exchange device and a cryogenic heat exchange device. The precooling heat exchange device performs preliminary liquefaction on the natural gas, and the cryogenic heat exchange device performs deep liquefaction on the natural gas. The remaining cold nitrogen in the cryogenic heat exchange device is returned to the precooling device for further preliminary precooling of the recovered natural gas. This invention achieves efficient natural gas recovery from decentralized gas fields through cascade precooling and deep adsorption, effectively reducing energy consumption and ensuring the safe and stable operation of the system.

Description

Technical Field

[0001] This invention relates to the field of natural gas recovery technology, and in particular to a decentralized natural gas recovery system and method for gas fields based on the cascade utilization of liquid nitrogen cold energy. Background Technology

[0002] As a clean and low-carbon energy source, the efficient utilization of natural gas is of great significance for optimizing the energy structure. However, in the process of natural gas extraction, transportation and processing, there are a large number of scattered gas sources that are not effectively utilized (mainly including: natural gas from marginal gas fields, pipeline maintenance and replacement gas, and venting air from gas facilities). These gas sources are characterized by scattered distribution, small total amount, unstable single-point reserves or limited existence time, making it difficult to connect them to pipelines for large-scale transportation.

[0003] Currently, liquefying natural gas is an effective way to solve its storage and long-distance transportation problems. Existing natural gas liquefaction technologies are mainly based on the principle of refrigeration cycles, which can be divided into two main categories: expansion refrigeration cycles (such as nitrogen expansion cycles and natural gas direct expansion cycles) and mixed refrigerant cycles. These technologies have been successfully applied in large-scale baseload liquefied natural gas (LNG) plants. However, their technical routes and application models have the following inherent defects and limitations when dealing with the aforementioned dispersed, small-scale gas sources: I. The contradiction between investment scale and economic efficiency. Traditional LNG liquefaction plants are intensive facilities with huge construction and supporting costs. Their economic efficiency is heavily dependent on large-scale gas sources of more than one million tons and long-term (usually more than 15 years) stable operation. However, for decentralized and intermittent gas sources with a daily processing capacity of less than several hundred thousand cubic meters, the return on investment for building fixed liquefaction plants is extremely low, and may not even cover the costs. This leads to a large amount of natural gas resources being forced to be directly vented or burned, which causes serious energy waste and environmental pollution.

[0004] Second, fixed deployment leads to a lack of mobility. Existing liquefaction plants all adopt a fixed construction model, with their site selection and construction based on specific gas source points. This "fixed plant, directional gas source" model is completely unsuitable for recovery scenarios where "gas sources are dispersed and locations are variable." When the gas source at a specific location is depleted or operations end, the fixed facilities built with huge investments face idleness or dismantling, unable to be moved to a new gas source point, lacking the necessary mobility and reuse value, thus failing to form an effective commercial recovery model.

[0005] Third, the process is complex and poorly adaptable to gas source conditions. Traditional liquefaction technology typically involves complex and large-scale refrigerant compression, cooling, separation, and circulation systems. Furthermore, it imposes strict requirements on the feed gas entering the core liquefaction module, necessitating a dedicated deep pretreatment system (such as acid removal, dehydration, and mercury removal) to remove impurities such as carbon dioxide, hydrogen sulfide, and moisture. This not only increases the overall system footprint, equipment investment, and operational complexity but also reduces the device's ability to quickly adapt to gas sources with different compositions and impurity contents.

[0006] IV. Constraints of Energy Efficiency and Operating Costs. The thermodynamic efficiency of liquefaction processes based on gas compression and expansion is limited by the Carnot cycle limit, and a significant amount of energy is consumed in the multi-stage compression process of the refrigerant. In small- to medium-scale applications, the system cannot replicate the economies of scale of large-scale plants, resulting in significantly higher energy consumption per unit of liquefaction (e.g., kWh / ton of LNG) and high operating costs, further weakening its economic feasibility for distributed gas source recovery.

[0007] Fifth, the construction period is long and the response is not rapid. A stationary liquefaction project takes several years from planning, design, procurement, civil construction, equipment installation to commissioning. This long construction process cannot meet the environmental and economic benefits requirements for rapid response and immediate recovery of vented or pilot-produced gases.

[0008] As explained above, existing natural gas liquefaction technologies are primarily based on compressor refrigeration cycles. Their technical solutions rely on a fixed, fully modular construction model and closed-loop, self-driven compression and refrigeration systems (such as mixed refrigerant cycles or expander cycles). These core characteristics fundamentally limit their application in distributed gas source recovery. Specifically, this approach requires the location, foundation pouring, and pipeline connection of large individual units such as compressors, cold boxes, and heat exchangers on-site, along with the construction of permanent plant structures. This "fixed site, modular installation" technical characteristic results in a complete loss of mobility for the equipment, with deployment cycles lasting several years, making it unsuitable for rapid response requirements such as air release scenarios. Secondly, its liquefaction cooling capacity comes from its own multi-stage compression-expansion-heat exchange closed-loop system. To achieve thermodynamic efficiency, this system inevitably includes complex rotating machinery, refrigerant proportioning, and control units. Therefore, the characteristics of "rigid process coupling and system complexity" lead to huge initial investment and high unit costs in small-scale operations due to the inability to achieve economies of scale, resulting in poor economic efficiency. Meanwhile, this scheme rigidly integrates the liquefaction core with the deep pretreatment process, requiring the feed gas to meet stringent standards before entering the cryogenic zone. This "dependence on front-end deep pretreatment" characteristic makes the system poorly adaptable to gas quality fluctuations and lacks process flexibility. It is precisely these three main technical characteristics—"fixed infrastructure," "closed-loop compression and refrigeration," and "rigidly coupled pretreatment"—that collectively lead to systemic defects in existing technologies, such as lack of flexibility, high investment thresholds, low energy efficiency, and insufficient adaptability, making them unsuitable for small- to medium-scale, decentralized natural gas recovery scenarios.

[0009] There is currently no effective solution to the problem that natural gas liquefaction and recovery systems in related technologies are characterized by high cost, poor mobility, and poor adaptability to gas source conditions, making them unsuitable for decentralized natural gas recovery scenarios.

[0010] Therefore, this invention proposes a decentralized gas field natural gas recovery system and method based on the cascade utilization of liquid nitrogen cold energy to overcome the shortcomings of existing technologies. Summary of the Invention

[0011] The purpose of this invention is to provide a decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy. By performing cascade precooling and deep adsorption on the recovered natural gas, efficient recovery of natural gas from decentralized gas fields can be achieved. This not only effectively reduces energy consumption but also ensures the safe and stable operation of the system, making it suitable for decentralized natural gas recovery scenarios.

[0012] Another objective of this invention is to provide a decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy. It adopts a modular assembly scheme, with each module using a skid-mounted design. The modules are connected by pipelines for convenient assembly, ensuring the mobility of the natural gas recovery system and achieving excellent mobility and rapid deployment capabilities. It is particularly suitable for distributed natural gas recovery scenarios.

[0013] The objective of this invention can be achieved through the following methods: This invention provides a decentralized natural gas recovery system for gas fields based on the cascade utilization of liquid nitrogen cold energy. The decentralized natural gas recovery system for gas fields based on the cascade utilization of liquid nitrogen cold energy includes a pretreatment skid-mounted module and a cryogenic liquefaction skid-mounted module. The pretreatment skid-mounted module includes: A precooling device for initially precooling the recovered natural gas; A first gas-liquid separation device is connected at its inlet to the outlet of the precooling device. The first gas-liquid separation device is used to perform gas-liquid separation processing on the recovered natural gas to obtain pure natural gas. An adsorption tower, the inlet of which is connected to the outlet of the first gas-liquid separation device, contains an adsorbent to dry and decarbonize the natural gas. The cryogenic liquefaction skid-mounted module includes: Liquid nitrogen storage device; A precooling heat exchange device has a first inlet and a second inlet. The first inlet of the precooling heat exchange device is connected to the liquid nitrogen storage device, and the second inlet of the precooling heat exchange device is connected to the outlet of the adsorption tower to perform preliminary liquefaction on the dried natural gas. A cryogenic heat exchanger is provided, wherein the inlet of the cryogenic heat exchanger is connected to the outlet of the precooling heat exchanger for deep liquefaction of the pre-liquefied natural gas; the nitrogen outlet of the cryogenic heat exchanger is connected to the precooling device; and the remaining cold nitrogen in the cryogenic heat exchanger is returned to the precooling device for preliminary precooling of the recovered natural gas.

[0014] In a preferred embodiment of the present invention, the pretreatment skid-mounted module further includes an energy recovery heat exchange device. The inlet of the energy recovery heat exchange device is connected to the outlet of the first gas-liquid separation device, and the outlet of the energy recovery heat exchange device is connected to the inlet of the adsorption tower. A heat exchange pipeline is provided between the adsorption tower and the energy recovery heat exchange device. The inlet and outlet of the heat exchange pipeline are respectively connected to the adsorption tower, and at least a portion of the heat exchange pipeline passes through the energy recovery heat exchange device. The dried natural gas in the adsorption tower circulates between the adsorption tower and the energy recovery heat exchange device to exchange heat and cool the dried natural gas in the adsorption tower.

[0015] In a preferred embodiment of the present invention, the pretreatment skid-mounted module further includes a natural gas recovery device, the inlet of which is connected to a pipeline for conveying the natural gas to be recovered, and the outlet of which is connected to the precooling device. A filtration and separation device for removing impurities and droplets from the natural gas is provided between the natural gas recovery device and the precooling device. The inlet of the filtration and separation device is connected to the outlet of the natural gas recovery device, and the outlet of the filtration and separation device is connected to the inlet of the precooling device. A pressure regulating valve is provided between the filtration and separation device and the precooling device.

[0016] In a preferred embodiment of the present invention, a nitrogen storage device is provided between the cryogenic heat exchange device and the precooling device, the nitrogen outlet of the cryogenic heat exchange device is connected to the inlet of the nitrogen storage device, and the outlet of the nitrogen storage device is connected to the precooling device; a temperature control device is provided on the pipeline between the outlet of the nitrogen storage device and the precooling device to regulate the temperature of the cold nitrogen returning to the precooling device.

[0017] In a preferred embodiment of the present invention, the outlet of the nitrogen storage device or the pipeline between the outlet of the nitrogen storage device and the precooling device is connected to the cryogenic heat exchanger via a backflush pipeline, so as to purge the cryogenic heat exchanger with nitrogen by means of cold nitrogen returning to the precooling device.

[0018] In a preferred embodiment of the present invention, there are two adsorption towers, each containing an adsorbent that adsorbs trace amounts of moisture and carbon dioxide from natural gas, and the adsorption tower is connected to a closed-loop regeneration skid-mounted module for desorbing and regenerating the adsorbent therein. In one of the two adsorption towers, the adsorption tower is in a state of adsorbing trace amounts of moisture and carbon dioxide in natural gas, and the closed-loop regeneration skid module performs desorption and regeneration treatment on the adsorbent in the other adsorption tower.

[0019] In a preferred embodiment of the present invention, the closed-loop regeneration skid-mounted module includes a first compression device, a regeneration heating device, a regeneration gas cooling device, and a second gas-liquid separation device, wherein the first compression device, the regeneration heating device, the adsorption tower, the regeneration gas cooling device, and the second gas-liquid separation device are sequentially connected in a closed loop; wherein... The first compression device is used to provide driving force to drive the regeneration gas circulating within the adsorption tower; The regeneration heating device is used to heat the circulating regeneration gas to the temperature required for regeneration. The high-temperature regeneration gas flows into the adsorption tower to desorb the water and carbon dioxide adsorbed in the adsorbent. The regeneration gas cooling device is used to cool the regeneration gas generated by the adsorption tower; The second gas-liquid separation device is used to separate the condensate generated after the regenerated gas is cooled.

[0020] In a preferred embodiment of the present invention, the cryogenic liquefaction skid-mounted module further includes a third gas-liquid separation device, wherein the product outlet of the cryogenic heat exchange device is connected to the inlet of the third gas-liquid separation device, and the third gas-liquid separation device is used to separate liquefied natural gas from evaporated gas. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy also has a storage and transportation module. The storage and transportation module includes a second compression device, a liquefied natural gas storage device, and an external transportation device. The inlet of the second compression device is connected to the evaporation gas outlet of the third gas-liquid separator, and the outlet of the second compression device is connected to the inlet of the natural gas recovery device. The liquefied natural gas storage device is installed on the external transportation device, and the inlet of the liquefied natural gas storage device is connected to the liquefied natural gas outlet of the third gas-liquid separator.

[0021] This invention provides a decentralized natural gas recovery method for gas fields based on the cascade utilization of liquid nitrogen cold energy. It is implemented using the aforementioned decentralized natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy. The decentralized natural gas recovery method for gas fields based on the cascade utilization of liquid nitrogen cold energy includes the following steps: Step S1: Introduce the recovered natural gas into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization, and sequentially pass the recovered natural gas through a pre-cooling device and a first gas-liquid separation device to perform preliminary pre-cooling and gas-liquid separation treatment to obtain pure natural gas. Step S2: The natural gas after gas-liquid separation enters the adsorption tower for drying and carbon removal. Step S3: The dried natural gas enters the pre-cooling heat exchange device, and liquid nitrogen is supplied to the pre-cooling heat exchange device through the liquid nitrogen storage device so that the dried natural gas can exchange heat with the liquid nitrogen and perform preliminary liquefaction of the dried natural gas; Step S4: The gas-liquid two-phase flow after preliminary liquefaction enters the cryogenic heat exchanger to further liquefy the preliminarily liquefied natural gas; Among them, the remaining cold nitrogen in the cryogenic heat exchanger is returned to the precooling device to perform preliminary precooling on the recovered natural gas; Step S5: Perform gas-liquid separation on the deeply liquefied natural gas; The separated liquefied natural gas is stored and transported off-site, while the separated vapors are reintroduced into the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy along with the recovered natural gas.

[0022] In a preferred embodiment of the present invention, in step S2, when the recovered natural gas is first introduced into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization, the energy recovery heat exchange device is turned off, and the natural gas after gas-liquid separation directly enters the adsorption tower through the bypass pipeline. When the temperature at the inlet of the energy recovery heat exchange device drops below the preset temperature, the energy recovery heat exchange device is turned on and the bypass pipeline is disconnected. The dried natural gas in the adsorption tower circulates between the adsorption tower and the energy recovery heat exchange device to exchange heat and cool the dried natural gas in the adsorption tower.

[0023] As described above, the characteristics and advantages of the decentralized gas field natural gas recovery system and method based on the cascade utilization of liquid nitrogen cold energy in this invention are: By combining the precooling device, the first gas-liquid separation device, and the adsorption tower, the staged precooling and deep adsorption of the recovered natural gas are achieved. Before the natural gas enters the cryogenic liquefaction skid module, it can be fully precooled and purified, eliminating the risk of freezing and blockage in the cryogenic liquefaction skid module from the source.

[0024] The remaining cold nitrogen in the cryogenic heat exchanger can be returned to pre-cool the recovered natural gas. Furthermore, the dried natural gas in the adsorption tower can be cooled through the energy recovery heat exchanger, achieving optimized integration of cold and hot logistics, efficient utilization of the remaining cold nitrogen, and helping to reduce the consumption of liquid nitrogen and improve the pre-cooling efficiency of natural gas.

[0025] By using a closed-loop regeneration skid-mounted module and the reinjection treatment of the separated evaporating gas, near-zero emissions of the regeneration process and product evaporating gas are achieved, greatly improving the overall recovery rate.

[0026] By using precooling heat exchangers and cryogenic heat exchangers, "parallel precooling + parallel cryogenic" can be achieved for natural gas. This staged liquefaction recovery method can reduce energy consumption and ensure the safe and stable operation of the system.

[0027] Each module adopts a skid-mounted design, and the modules are connected by pipelines for easy assembly, ensuring the mobility of the natural gas recovery system and realizing the system's excellent mobility and rapid deployment capabilities, making it particularly suitable for distributed natural gas recovery scenarios. Attached Figure Description

[0028] The following figures are intended only to illustrate and explain the present invention and do not limit the scope of the invention. Wherein: Figure 1 This is a structural block diagram of the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, as described in this invention.

[0029] The reference numerals in the accompanying drawings of this invention are: 1. Pretreatment skid-mounted module; 101. Natural gas recovery unit; 102. Filtration and separation unit; 103. Pressure regulating valve; 104. Precooling unit; 105. First gas-liquid separation unit; 106. Energy recovery heat exchanger; 107. Adsorption tower; 108. Heat exchange pipeline; 2. Cryogenic liquefaction skid-mounted module; 201. Liquid nitrogen storage unit; 202. Liquid nitrogen pump; 203. Precooling heat exchanger; 2031. First precooling heat exchanger; 2032. Second precooling heat exchanger; 204. Cryogenic heat exchanger The equipment includes: 2041, First cryogenic heat exchanger; 2042, Second cryogenic heat exchanger; 205, Third gas-liquid separation device; 3, Storage and transportation module; 301, Second compression device; 302, Liquefied natural gas storage device; 303, Transportation device; 4, Closed-loop regeneration skid-mounted module; 401, First compression device; 402, Regeneration heating device; 403, Regeneration gas cooling device; 404, Second gas-liquid separation device; 5, Nitrogen storage device; 6, Temperature control device; 7, Ambient temperature nitrogen injection pipeline. Detailed Implementation

[0030] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0031] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] Implementation Method 1

[0034] like Figure 1 As shown, this invention provides a decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy. This decentralized gas field natural gas recovery system includes a pretreatment skid-mounted module 1 and a cryogenic liquefaction skid-mounted module 2, wherein: The pretreatment skid-mounted module 1 includes a precooling device 104, a first gas-liquid separator 105, and an adsorption tower 107. The precooling device is used to precool the recovered natural gas. The inlet of the first gas-liquid separator 105 is connected to the outlet of the precooling device 104. The first gas-liquid separator 105 is used to perform gas-liquid separation on the recovered natural gas to remove impurities and droplets from the natural gas and obtain pure natural gas. The inlet of the adsorption tower 107 is connected to the outlet of the first gas-liquid separator 105. The adsorption tower contains an adsorbent to dry and decarbonize the natural gas. The cryogenic liquefaction skid-mounted module 2 includes a liquid nitrogen storage device 201, a precooling heat exchange device 203, and a cryogenic heat exchange device 204. The precooling heat exchange device 203 has a first inlet and a second inlet. The first inlet of the precooling heat exchange device 203 is connected to the liquid nitrogen storage device 201, and the second inlet of the precooling heat exchange device 203 is connected to the outlet of the adsorption tower 107. The precooling heat exchange device 203 performs preliminary liquefaction on the natural gas after it has been dried by the adsorption tower 107. The inlet of the cryogenic heat exchange device 204 is connected to the outlet of the precooling heat exchange device 203. The cryogenic heat exchange device 204 performs deep liquefaction on the pre-liquefied natural gas. The nitrogen outlet of the cryogenic heat exchanger 204 is connected to the precooling device 104. The remaining cold nitrogen in the cryogenic heat exchanger 204 is returned to the precooling device 104 to precool the recovered natural gas, so as to ensure that the recovered natural gas can be precooled to -30 to -50°C and most of the condensate and heavy hydrocarbons contained therein can be preliminarily separated.

[0035] In this invention, the recovered natural gas can be vented air collected from decentralized gas fields. Vented air includes, but is not limited to, gas from gas fields, gas from peripheral wells, and pipeline gas.

[0036] In this invention, the first gas-liquid separation device 105 may be, but is not limited to, a filter separator.

[0037] In this invention, the liquid nitrogen storage device 201 may be, but is not limited to, a liquid nitrogen storage tank.

[0038] This invention, through the cooperation of the precooling device 104, the first gas-liquid separation device 105, and the adsorption tower 107, achieves tiered precooling and deep adsorption of the recovered natural gas. Before the natural gas enters the cryogenic liquefaction skid-mounted module 2, it is fully precooled and purified, fundamentally eliminating the risk of freezing and blockage in the cryogenic liquefaction skid-mounted module 2. Furthermore, the remaining cold nitrogen in the cryogenic heat exchanger 204 within the cryogenic liquefaction skid-mounted module 2 can be returned to the precooling device 104 for preliminary precooling of the recovered natural gas. This efficient utilization of the remaining cold nitrogen helps reduce liquid nitrogen consumption and improves the precooling efficiency of the natural gas.

[0039] In addition, in this invention, the precooling heat exchange device 203 and the cryogenic heat exchange device 204 work together to achieve the step-by-step liquefaction of natural gas. This step-by-step liquefaction recovery method can reduce energy consumption and ensure the safe and stable operation of the system.

[0040] In an optional embodiment of the present invention, such as Figure 1 As shown, the pretreatment skid-mounted module 1 also includes an energy recovery heat exchanger 106. The inlet of the energy recovery heat exchanger 106 is connected to the outlet of the first gas-liquid separation device 105, and the outlet of the energy recovery heat exchanger 106 is connected to the inlet of the adsorption tower 107. A heat exchange pipeline 108 is provided between the adsorption tower 107 and the energy recovery heat exchanger 106. The inlet and outlet of the heat exchange pipeline 108 are respectively connected to the adsorption tower 107, and the connection points of the inlet and outlet of the heat exchange pipeline 108 with the adsorption tower 107 are located within the adsorbent in the adsorption tower. Downstream, at least a portion of the heat exchange pipeline 108 passes through the energy recovery heat exchange device 106, allowing the dried natural gas in the adsorption tower 107 to circulate between the adsorption tower 107 and the energy recovery heat exchange device 106 via the heat exchange pipeline 108. This allows the low-temperature natural gas, initially introduced into the energy recovery heat exchange device 106 by the first gas-liquid separation device 105, to exchange heat and cool the dried natural gas in the adsorption tower 107. The cooled natural gas in the adsorption tower 107, after heat exchange and cooling by the energy recovery heat exchange device 106, is then sent to the pre-cooling heat exchange device 203 for preliminary liquefaction. This transfers the remaining cold energy of the low-temperature material (pre-cooled natural gas) in the recovery system to the high-temperature material (purified and dried natural gas) that requires cooling, thereby achieving the recycling of internal cooling capacity, reducing liquid nitrogen consumption, and improving the energy efficiency and economy of the entire recovery system.

[0041] In an optional embodiment of the present invention, such as Figure 1As shown, the pretreatment skid-mounted module 1 also includes a natural gas recovery device 101. The inlet of the natural gas recovery device 101 is connected to a pipeline transporting the natural gas to be recovered, and the outlet of the natural gas recovery device 101 is connected to the inlet of the precooling device 104. The natural gas recovery device 101 is used to centrally collect the natural gas to be liquefied and then quantitatively inject it into the system according to actual conditions. The natural gas recovery device 101 can be, but is not limited to, a natural gas storage tank. Alternatively, the natural gas recovery device 101 can also be a section of controllable on / off natural gas transmission pipeline.

[0042] Furthermore, such as Figure 1 As shown, a filtration and separation device 102 is installed between the natural gas recovery device 101 and the precooling device 104 to remove impurities and droplets from the natural gas. The inlet of the filtration and separation device 102 is connected to the outlet of the natural gas recovery device 101, and the outlet of the filtration and separation device 102 is connected to the inlet of the precooling device 104. A pressure regulating valve 103 is installed between the filtration and separation device 102 and the precooling device 104. Before the recovered natural gas enters the precooling device 104, it is filtered by the filtration and separation device 102 to remove impurities and droplets. The filtration and separation device 102 may be, but is not limited to, a filter separator.

[0043] The bypass pipeline can be directly led out from the natural gas source, natural gas recovery device 101 or filtration and separation device 102, and connected to the inlet of adsorption tower 107 through the bypass pipeline. Gas is directly supplied to adsorption tower 107 through the bypass pipeline. Since pipeline gas has better cleanliness, it can ensure that the natural gas entering adsorption tower 107 is cleaner.

[0044] In an optional embodiment of the present invention, such as Figure 1 As shown, a nitrogen storage device 5 is provided between the cryogenic heat exchanger 204 and the precooling device 104. The nitrogen outlet of the cryogenic heat exchanger 204 is connected to the inlet of the nitrogen storage device 5, and the outlet of the nitrogen storage device 5 is connected to the precooling device 104. The cold nitrogen after heat exchange in the cryogenic heat exchanger 204 can be centrally collected through the nitrogen storage device 5 and supplied with the nitrogen required for purging or to the precooling device 104 as needed. The nitrogen storage device 5 can be, but is not limited to, a nitrogen storage tank.

[0045] Furthermore, such as Figure 1As shown, a temperature control device 6 is installed on the pipeline between the outlet of the nitrogen storage device 5 and the precooling device 104 to regulate the temperature of the cold nitrogen returning to the precooling device 104. The temperature control device 6 can be limited to a pressure regulating valve. During use, the nitrogen pressure is changed by the pressure regulating valve, thereby coarsely adjusting its base temperature. Additionally, a room-temperature nitrogen injection pipeline 7 is connected externally to the outlet of the nitrogen storage device 5 or the pipeline between the outlet of the nitrogen storage device 5 and the precooling device 104. This pipeline replenishes room-temperature nitrogen, and by controlling the injection volume, it can coordinate with the nitrogen output from the nitrogen storage device 5 to precisely control the temperature of the nitrogen returning to the flow path within a preset range, thus providing a stable and controllable cold source for the precooling device 104.

[0046] In this embodiment, the cold nitrogen gas returned to the precooling device 104 is generally controlled at around -60°C.

[0047] Furthermore, such as Figure 1 As shown, the outlet of the nitrogen storage device 5 or the pipeline between the outlet of the nitrogen storage device 5 and the precooling device 104 is connected to the cryogenic heat exchanger 204 via a backflush pipeline. This allows the cryogenic heat exchanger 204 to be purged with cold nitrogen returning to the precooling device 104, thereby achieving the purpose of purging and thawing the cryogenic heat exchanger 204. Alternatively, thawing can be achieved by injecting a thawing agent (such as methanol or ethylene diether) through the thawing agent injection port on the cryogenic heat exchanger 204.

[0048] In an optional embodiment of the present invention, such as Figure 1As shown, there are two adsorption towers 107 connected in parallel. Each adsorption tower 107 contains an adsorbent (such as a molecular sieve) for adsorbing trace amounts of moisture and carbon dioxide from natural gas. The adsorption tower 107 is connected to a closed-loop regeneration skid-mounted module 4 for desorbing and regenerating the adsorbent within it. In one of the two adsorption towers 107, the adsorption tower 107 is in the state of adsorbing trace amounts of moisture and carbon dioxide from natural gas (i.e., working mode), while the closed-loop regeneration skid-mounted module 4 performs desorption and regeneration treatment on the adsorbent in the other adsorption tower 107 (i.e., regeneration mode). The function of adsorption tower 107 is to remove trace amounts of moisture and carbon dioxide remaining in natural gas after preliminary pre-cooling and gas-liquid separation. Two adsorption towers 107 operate in parallel. One tower, during adsorption, can reduce the water dew point of the natural gas to below -70°C and the carbon dioxide content to below 50 ppm, ensuring that the natural gas entering the cryogenic liquefaction skid module 2 is extremely dry and clean. This fundamentally solves the freezing and blockage problem caused by moisture and / or carbon dioxide condensation during subsequent ultra-low temperature heat exchange. The other adsorption tower 107 simultaneously performs heating, purging, desorption, cooling, and pressurization operations through the closed-loop regeneration skid module 4, preparing for the switching operation of adsorption tower 107. The two adsorption towers 107 can be periodically controlled by a programmable control valve to alternately intervene in the system, achieving automatic switching operations and realizing continuous production and near-zero emission high-efficiency and stable operation.

[0049] Specifically, such as Figure 1 As shown, the closed-loop regeneration skid-mounted module 4 includes a first compression device 401, a regeneration heating device 402, a regeneration gas cooling device 403, and a second gas-liquid separator 404. The first compression device 401, regeneration heating device 402, adsorption tower 107, regeneration gas cooling device 403, and second gas-liquid separator 404 are sequentially connected in a closed loop. Specifically, the inlet of the first compression device 401 is connected to the outlet of the second gas-liquid separator 404, the outlet of the first compression device 401 is connected to the inlet of the regeneration heating device 402, the outlet of the regeneration heating device 402 is connected to the inlet of the adsorption tower 107, the outlet of the adsorption tower 107 is connected to the inlet of the regeneration gas cooling device 403, and the outlet of the regeneration gas cooling device 403 is connected to the inlet of the second gas-liquid separator 404. The first compression device 401 may be, but is not limited to, a circulating compressor. The first compression device 401 is used to provide driving force to drive the regeneration gas circulating within the adsorption tower 107. The regeneration heating device 402 can be, but is not limited to, a heater. The regeneration heating device 402 is used to heat the circulating regeneration gas to the temperature required for regeneration. The high-temperature regeneration gas flows into the adsorption tower 107 to desorb the water and carbon dioxide adsorbed in the adsorbent. The regeneration gas cooling device 404 may be, but is not limited to, a cooler, and is used to cool the regeneration gas generated by the adsorption tower 107. The second gas-liquid separation device 405 may be, but is not limited to, a gas-liquid separator, and is used to separate the condensate generated after the regenerated gas is cooled.

[0050] During use, the closed-loop regeneration skid-mounted module 4 drives the regeneration gas to circulate in a closed loop via the first compression device 401. After passing through the regeneration heating device 402 to heat up and desorb the moisture (water vapor) in the adsorbent, the regeneration gas and water vapor then enter the regeneration gas cooling device 404 to cool down and condense the water vapor. Finally, the second gas-liquid separation device 405 separates and discharges the condensate, and the dried regeneration gas re-enters the loop, thereby realizing the online regeneration of the adsorbent and the reuse of the circulating gas. The entire process is isolated from the adsorption tower 107 in operation, ensuring that the regeneration process is efficient and stable, and can achieve near-zero emissions.

[0051] In an optional embodiment of the present invention, such as Figure 1 As shown, there are two precooling heat exchangers 203 connected in parallel, with one as a backup. The precooling heat exchangers 203 lower the temperature of the natural gas to -90℃, achieving the purpose of preliminary liquefaction.

[0052] In an optional embodiment of the present invention, such as Figure 1 As shown, there are two cryogenic heat exchangers 204 connected in parallel, with one serving as a backup. In the cryogenic heat exchanger 204, liquid nitrogen undergoes a secondary heat exchange with natural gas, lowering the temperature of the natural gas to -162℃, thus achieving deep liquefaction.

[0053] In this embodiment, as Figure 1 As shown, the precooling heat exchange device 203 includes a first precooling heat exchanger 2031 and a second precooling heat exchanger 2032 connected in parallel, and the cryogenic heat exchange device 204 includes a first cryogenic heat exchanger 2041 and a second cryogenic heat exchanger 2042 connected in parallel. The outlet of the first precooling heat exchanger 2031 is connected to the inlets of the first cryogenic heat exchanger 2041 and the second cryogenic heat exchanger 2042 in a switchable manner, and the outlet of the second precooling heat exchanger 2032 is connected to the inlets of the first cryogenic heat exchanger 2041 and the second cryogenic heat exchanger 2042 in a switchable manner. This allows for switching the connection relationship between different precooling heat exchangers and cryogenic heat exchangers according to actual operation, thereby avoiding the impact of freezing blockage on the normal operation of natural gas liquefaction.

[0054] In an optional embodiment of the present invention, such as Figure 1As shown, the cryogenic liquefaction skid-mounted module 2 also includes a third gas-liquid separator 205. The product outlet of the cryogenic heat exchanger 204 is connected to the inlet of the third gas-liquid separator 205. The third gas-liquid separator 205 is used to separate liquefied natural gas (LNG) from unliquefied boil-off gas (BOG, mainly composed of methane). The third gas-liquid separator 205 can be, but is not limited to, a gas-liquid separator.

[0055] Furthermore, such as Figure 1 As shown, the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy also includes a storage and transportation module 3. The storage and transportation module 3 includes a second compression unit 301, a liquefied natural gas (LNG) storage unit 302, and an external transportation unit 303. The inlet of the second compression unit 301 is connected to the evaporation gas outlet of the third gas-liquid separator 205, and the outlet of the second compression unit 301 is connected to the inlet of the natural gas recovery unit 101. The LNG storage unit 302 is installed on the external transportation unit 303, and its inlet is connected to the LNG outlet of the third gas-liquid separator 205. After the LNG is separated from the unliquefied evaporation gas (BOG) by the third gas-liquid separator 205, the LNG enters the LNG storage unit 302 for storage or external transportation. The separated BOG is reintroduced into the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy under the drive of the second compression unit 301, thereby maximizing resource utilization and achieving near-zero emissions.

[0056] The second compression device 301 may be, but is not limited to, a compressor.

[0057] The liquefied natural gas storage device 302 may be, but is not limited to, an LNG storage tank.

[0058] The transport device 303 can be, but is not limited to, a tank truck. Of course, it can also be a transport pipeline.

[0059] The features and advantages of the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy of the present invention are as follows: In this decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, the precooling device 104, the first gas-liquid separation device 105, and the adsorption tower 107 work together to achieve cascade precooling and deep adsorption of the recovered natural gas. Before the natural gas enters the cryogenic liquefaction skid module 2, it can be fully precooled and purified, thus eliminating the risk of freezing and blockage in the cryogenic liquefaction skid module 2 from the source.

[0060] Second, this decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy can return the remaining cold nitrogen in the cryogenic heat exchange device 204 to pre-cool the recovered natural gas. Furthermore, the dried natural gas in the adsorption tower 107 can be cooled by heat exchange through the energy recovery heat exchange device 106, thereby achieving optimized integration of cold and hot logistics, efficient utilization of the remaining cold nitrogen, and helping to reduce the consumption of liquid nitrogen and improve the pre-cooling efficiency of natural gas.

[0061] Third, in this decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, the near-zero emission of the regeneration process and the product evaporation gas is achieved through the closed-loop regeneration skid-mounted module 4 and the reinjection treatment of the separated evaporation gas, which greatly improves the overall recovery rate.

[0062] Fourth, in the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, the pre-cooling heat exchange device 203 and the cryogenic heat exchange device 204 can realize the "parallel pre-cooling + parallel cryogenic" of natural gas. This staged liquefaction recovery method can reduce energy consumption and ensure the safe and stable operation of the system.

[0063] Fifth, in this decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, each module adopts a skid-mounted design, and the modules are connected by pipelines for convenient assembly, ensuring the mobility of the natural gas recovery system and realizing the system's excellent mobility and rapid deployment capabilities, making it particularly suitable for distributed natural gas recovery scenarios.

[0064] Implementation Method 2

[0065] This invention provides a decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy. It is implemented using the aforementioned decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy. The decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy includes the following steps: Step S1: Slowly introduce the recovered natural gas into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization, so that the system is gradually pressurized to the preset operating pressure; then, the recovered natural gas is subjected to preliminary pre-cooling and gas-liquid separation treatment through the pre-cooling device 104 and the first gas-liquid separation device 105 in sequence to obtain pure natural gas. In step S1, when natural gas is first introduced, it is necessary to ensure that the natural gas flows through the entire pretreatment skid module 1 and produces the first batch of qualified dry natural gas.

[0066] Step S2: The natural gas after gas-liquid separation enters the adsorption tower 107 for drying and carbon removal. In the initial stage of introducing recovered natural gas into a decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy, the energy recovery heat exchange device 106 is shut down, and the gas-liquid separated natural gas directly enters the adsorption tower 107 through a bypass pipeline. This initial portion of natural gas does not pass through any heat exchange device and, after drying, directly enters the cryogenic liquefaction skid-mounted module 2, ensuring that the cryogenic liquefaction skid-mounted module 2 can obtain a qualified gas source to start producing liquefied natural gas (LNG) and vaporized gas, and has surplus cold nitrogen, which can then provide cooling for the precooling device 105.

[0067] When the temperature at the inlet of the energy recovery heat exchanger 106 drops below a preset temperature (e.g., -30℃), the energy recovery heat exchanger 106 is turned on and the bypass pipeline is disconnected. The dried natural gas in the adsorption tower 107 circulates between the adsorption tower 107 and the energy recovery heat exchanger 106 to exchange heat and cool the dried natural gas in the adsorption tower 107. This switching process needs to be carried out slowly to avoid causing drastic disturbances in the flow rate and / or temperature of the downstream cryogenic liquefaction skid-mounted module 2. After the switching is completed, the system enters a stable operating state. The pre-cooled natural gas is reheated in the energy recovery heat exchanger 106, while the purified natural gas is pre-cooled, achieving efficient energy integration. The core idea of ​​the entire startup process is: first establish the purification process, and then gradually introduce cold energy for integration and optimization.

[0068] Step S3: The dried natural gas enters the pre-cooling heat exchanger 203. Liquid nitrogen is supplied to the pre-cooling heat exchanger 203 through the liquid nitrogen storage device 201 so that the dried natural gas can exchange heat with the liquid nitrogen and the temperature drops to about -90℃, thus performing preliminary liquefaction of the dried natural gas. Step S4: The gas-liquid two-phase flow after preliminary liquefaction enters the cryogenic heat exchanger 204, where the temperature drops to about -162℃, and the preliminary liquefied natural gas is further liquefied. Among them, the remaining cold nitrogen in the cryogenic heat exchanger 204 is returned to the precooling device 104 to precool the recovered natural gas.

[0069] Step S5: Perform gas-liquid separation on the deeply liquefied natural gas, wherein the separated liquefied natural gas is stored and transported off-site, and the separated vapor gas is reintroduced into the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy along with the recovered natural gas.

[0070] In an optional embodiment of the present invention, before step S1 above, a gas tightness test needs to be performed on the natural gas recovery system: that is, after connecting the pipelines between each module, nitrogen is introduced into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization by liquid nitrogen storage device 201 and / or ambient temperature nitrogen injection pipeline 7 until the actual pressure in the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization is greater than the preset pressure (generally the actual pressure is 1.1-1.2 times the preset pressure), and maintained for a preset time. All welds, flanges and valve connections are checked using leak detection fluid or instruments to ensure that the system is leak-free.

[0071] Furthermore, after conducting the airtightness test, at least one outlet in the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization is opened to depressurize. After depressurization, nitrogen is introduced into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization through the liquid nitrogen storage device 201 and / or the ambient temperature nitrogen injection pipeline 7 to purge until the oxygen content in the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization is lower than a preset oxygen content threshold (1%), thereby eliminating the risk of explosion.

[0072] In an optional embodiment of the present invention, when the cryogenic heat exchanger 204 freezes and becomes blocked, the remaining cold nitrogen in the cryogenic heat exchanger 204 is conditioned and then returned to the cryogenic heat exchanger 204 for nitrogen purging and thawing, or a thawing agent is injected into the cryogenic heat exchanger 204 for thawing.

[0073] Traditional pretreatment typically employs separate dehydration and hydrocarbon removal units, resulting in lengthy processes and purification blind spots. In contrast, the pretreatment skid-mounted module 1 in this application integrates deep dehydration and heavy hydrocarbon removal, combining precooling, gas-liquid separation, and a parallel dual adsorption tower 107 for natural gas adsorption drying. This allows the recovered natural gas, after precooling to -30 to -50°C, to initially separate most of the condensate and heavy hydrocarbons before entering the adsorption tower 107 for deep purification. This invention, through the pretreatment skid-mounted module 1, efficiently produces deeply purified carbonized natural gas, providing extremely high-purity natural gas feedstock for subsequent cryogenic liquefaction. It fundamentally solves the problem of freezing and clogging in the cryogenic heat exchanger 204, and achieves efficient recovery and utilization of the system's cooling capacity through the energy recovery heat exchanger 106, thereby reducing overall energy consumption.

[0074] To ensure system stability, this invention designs a closed-loop regeneration skid-mounted module 4 for the adsorbent regeneration process in adsorption tower 107. This module forms an independent regeneration gas flow loop. This design not only controls the regeneration temperature, ensuring thorough adsorbent regeneration and extending its lifespan, but more importantly, it isolates the regeneration process from the main process through the switching operation of the two adsorption towers 107. This reduces material loss and environmental pollution caused by regeneration gas emissions, improving the environmental friendliness and stability of the process. Through system integration, it achieves efficient, stable, and coordinated deep purification of complex gas source components from gas fields and peripheral gas wells. Therefore, this invention's decentralized gas field natural gas recovery method based on liquid nitrogen cold energy cascade utilization, through ingenious process design and cold energy integration, achieves efficient, near-zero emission liquefaction recovery of incoming gas while ensuring high mobility. It is particularly suitable for natural gas recovery scenarios from distributed small and medium-sized gas sources.

[0075] The decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy of the present invention also has the same characteristics and advantages as the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy described above, and will not be repeated here.

[0076] It should be noted that in the description of this application, the terms "first," "second," etc., are used only for descriptive purposes and to distinguish similar objects; there is no order between them, nor should they be construed as indicating or implying relative importance. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0077] The various embodiments described in this specification are presented in a progressive manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0078] The above are merely a few embodiments of the present invention. Although the embodiments disclosed in the present invention are as described above, the content is only for the purpose of facilitating understanding of the present invention and is not intended to limit the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A decentralized natural gas recovery system for gas fields based on the cascade utilization of liquid nitrogen cold energy, characterized in that, The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy includes a pretreatment skid-mounted module and a cryogenic liquefaction skid-mounted module. The pretreatment skid-mounted module includes: A precooling device for initially precooling the recovered natural gas; A first gas-liquid separation device is connected at its inlet to the outlet of the precooling device. The first gas-liquid separation device is used to perform gas-liquid separation processing on the recovered natural gas to obtain pure natural gas. An adsorption tower, the inlet of which is connected to the outlet of the first gas-liquid separation device, contains an adsorbent to dry and decarbonize the natural gas. The cryogenic liquefaction skid-mounted module includes: Liquid nitrogen storage device; A precooling heat exchange device has a first inlet and a second inlet. The first inlet of the precooling heat exchange device is connected to the liquid nitrogen storage device, and the second inlet of the precooling heat exchange device is connected to the outlet of the adsorption tower to perform preliminary liquefaction on the dried natural gas. A cryogenic heat exchanger is provided, wherein the inlet of the cryogenic heat exchanger is connected to the outlet of the precooling heat exchanger for deep liquefaction of the pre-liquefied natural gas; the nitrogen outlet of the cryogenic heat exchanger is connected to the precooling device; and the remaining cold nitrogen in the cryogenic heat exchanger is returned to the precooling device for preliminary precooling of the recovered natural gas.

2. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 1, characterized in that, The pretreatment skid-mounted module also includes an energy recovery heat exchange device. The inlet of the energy recovery heat exchange device is connected to the outlet of the first gas-liquid separator, and the outlet of the energy recovery heat exchange device is connected to the inlet of the adsorption tower. A heat exchange pipeline is provided between the adsorption tower and the energy recovery heat exchange device. The inlet and outlet of the heat exchange pipeline are respectively connected to the adsorption tower, and at least a portion of the heat exchange pipeline passes through the energy recovery heat exchange device. The dried natural gas in the adsorption tower circulates between the adsorption tower and the energy recovery heat exchange device to exchange heat and cool the dried natural gas in the adsorption tower.

3. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 1, characterized in that, The pretreatment skid-mounted module also includes a natural gas recovery device, the inlet of which is connected to a pipeline for transporting the natural gas to be recovered, and the outlet of which is connected to the precooling device. A filtration and separation device for removing impurities and droplets from the natural gas is provided between the natural gas recovery device and the precooling device. The inlet of the filtration and separation device is connected to the outlet of the natural gas recovery device, and the outlet of the filtration and separation device is connected to the inlet of the precooling device. A pressure regulating valve is provided between the filtration and separation device and the precooling device.

4. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 1, characterized in that, A nitrogen storage device is provided between the cryogenic heat exchanger and the precooling device. The nitrogen outlet of the cryogenic heat exchanger is connected to the inlet of the nitrogen storage device, and the outlet of the nitrogen storage device is connected to the precooling device. A temperature control device is provided on the pipeline between the outlet of the nitrogen storage device and the precooling device to regulate the temperature of the cold nitrogen returning to the precooling device.

5. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 4, characterized in that, The outlet of the nitrogen storage device or the pipeline between the outlet of the nitrogen storage device and the precooling device is connected to the cryogenic heat exchanger via a backflush pipeline, so as to purge the cryogenic heat exchanger with nitrogen by returning cold nitrogen to the precooling device.

6. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 1, characterized in that, The adsorption towers are of two types, each containing an adsorbent that adsorbs trace amounts of moisture and carbon dioxide from natural gas. The adsorption towers are connected to a closed-loop regeneration skid-mounted module for desorbing and regenerating the adsorbent within them. In one of the two adsorption towers, the adsorption tower is in a state of adsorbing trace amounts of moisture and carbon dioxide in natural gas, and the closed-loop regeneration skid module performs desorption and regeneration treatment on the adsorbent in the other adsorption tower.

7. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 6, characterized in that, The closed-loop regeneration skid-mounted module includes a first compression device, a regeneration heating device, a regeneration gas cooling device, and a second gas-liquid separation device, wherein the first compression device, the regeneration heating device, the adsorption tower, the regeneration gas cooling device, and the second gas-liquid separation device are sequentially connected in a closed loop; wherein... The first compression device is used to provide driving force to drive the regeneration gas circulating within the adsorption tower; The regeneration heating device is used to heat the circulating regeneration gas to the temperature required for regeneration. The high-temperature regeneration gas flows into the adsorption tower to desorb the water and carbon dioxide adsorbed in the adsorbent. The regeneration gas cooling device is used to cool the regeneration gas generated by the adsorption tower; The second gas-liquid separation device is used to separate the condensate generated after the regenerated gas is cooled.

8. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in claim 2, characterized in that, The cryogenic liquefaction skid-mounted module also includes a third gas-liquid separator. The product outlet of the cryogenic heat exchanger is connected to the inlet of the third gas-liquid separator. The third gas-liquid separator is used to separate liquefied natural gas from evaporated gas. The decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy also has a storage and transportation module. The storage and transportation module includes a second compression device, a liquefied natural gas storage device, and an external transportation device. The inlet of the second compression device is connected to the evaporation gas outlet of the third gas-liquid separator, and the outlet of the second compression device is connected to the inlet of the natural gas recovery device. The liquefied natural gas storage device is installed on the external transportation device, and the inlet of the liquefied natural gas storage device is connected to the liquefied natural gas outlet of the third gas-liquid separator.

9. A decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy, implemented using the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy as described in any one of claims 1 to 8, characterized in that, The decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy includes the following steps: Step S1: Introduce the recovered natural gas into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization, and sequentially pass the recovered natural gas through a pre-cooling device and a first gas-liquid separation device to perform preliminary pre-cooling and gas-liquid separation treatment to obtain pure natural gas. Step S2: The natural gas after gas-liquid separation enters the adsorption tower for drying and carbon removal. Step S3: The dried natural gas enters the pre-cooling heat exchange device, and liquid nitrogen is supplied to the pre-cooling heat exchange device through the liquid nitrogen storage device so that the dried natural gas can exchange heat with the liquid nitrogen and perform preliminary liquefaction of the dried natural gas; Step S4: The gas-liquid two-phase flow after preliminary liquefaction enters the cryogenic heat exchanger to further liquefy the preliminarily liquefied natural gas; Among them, the remaining cold nitrogen in the cryogenic heat exchanger is returned to the precooling device to perform preliminary precooling on the recovered natural gas; Step S5: Perform gas-liquid separation on the deeply liquefied natural gas; The separated liquefied natural gas is stored and transported off-site, while the separated vapors are reintroduced into the decentralized gas field natural gas recovery system based on the cascade utilization of liquid nitrogen cold energy along with the recovered natural gas.

10. The decentralized gas field natural gas recovery method based on the cascade utilization of liquid nitrogen cold energy as described in claim 9, characterized in that, In step S2, when the recovered natural gas is first introduced into the decentralized gas field natural gas recovery system based on liquid nitrogen cold energy cascade utilization, the energy recovery heat exchange device is shut down, and the natural gas after gas-liquid separation directly enters the adsorption tower through the bypass pipeline. When the temperature at the inlet of the energy recovery heat exchange device drops below the preset temperature, the energy recovery heat exchange device is turned on and the bypass pipeline is disconnected. The dried natural gas in the adsorption tower circulates between the adsorption tower and the energy recovery heat exchange device to exchange heat and cool the dried natural gas in the adsorption tower.

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