Oil gas condensing and recovering system and method with coolant pre-cooling and cold energy step recovery

Abstract

This invention relates to the technical field of oil and gas recovery and treatment, and discloses an oil and gas condensation recovery system and method with refrigerant precooling and cascaded cold energy recovery. The system consists of a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system, a liquid hydrocarbon recovery unit, a tail gas treatment unit, and an automatic control unit. The precooling heat exchanger uses a refrigerant at -3℃ to -10℃ for indirect heat exchange, stably reducing the oil and gas temperature to -2℃ to -4℃, removing water vapor and heavy hydrocarbons. The primary and secondary cryogenic heat exchangers operate alternately in dual channels, working in conjunction with a cascade refrigeration unit to gradually cool the oil and gas to -20℃ to -40℃ and -65℃ to -75℃, respectively. The high-temperature refrigerant in the unit self-defrosts, ensuring continuous operation. The refrigerant circulation system and the cryogenic refrigeration system operate independently without interference, reducing the overall system failure risk and improving long-term reliability and maintenance convenience. This invention features precise temperature control, high cold energy utilization, no frost or blockage, continuous and stable operation, and combines environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the technical field of oil and gas recovery and treatment, and more specifically, to an oil and gas condensation recovery system and method that combines refrigerant precooling and cascade recovery of cooling capacity. Background Technology

[0002] In the petrochemical industry, the oil and gas (VOCs) generated during the storage and transportation of oil products not only cause environmental pollution but also lead to the economic loss of a large number of light hydrocarbon components. Oil and gas recovery technology liquefies and recovers condensable hydrocarbon components in oil and gas, which has both environmental and economic benefits. At present, the condensation method is one of the mature oil and gas recovery technologies in industry. Its basic principle is to use a multi-stage refrigeration system to gradually cool the oil and gas to about -70°C, so that the hydrocarbon components are condensed and liquefied and separated in stages.

[0003] Existing condensation-based oil and gas recovery systems typically employ a multi-stage cryogenic process flow consisting of a heat exchanger, a precooler, a primary condenser, and a secondary condenser. The oil and gas first exchange heat with cryogenically treated low-temperature lean oil and gas in the heat exchanger to achieve initial cold energy recovery. Subsequently, the oil and gas are sequentially cooled to approximately 4°C (ideal value) by the precooler, then to approximately -25°C by the primary condenser, and finally to approximately -70°C by the secondary condenser, completing multi-stage condensation and liquefaction separation. The cryogenically treated low-temperature lean oil and gas is then returned to the heat exchanger in a reverse direction, achieving cascaded recovery and utilization of the gas path's cold energy.

[0004] However, the aforementioned traditional processes have the following prominent problems in actual operation: First, the precooling process suffers from large temperature fluctuations and poor control precision. Traditional precoolers mainly rely on the cooling capacity provided by the low-temperature lean oil and gas after separation for heat exchange. When the ambient temperature is low, the temperature of the oil and gas after precooling may drop below 0°C, causing ice blockage inside the heat exchanger. When the ambient temperature is high, the temperature after precooling may be as high as 20°C or more, resulting in a large amount of water vapor in the oil and gas being unable to be removed, causing severe frost and ice formation after entering the subsequent cryogenic unit.

[0005] Secondly, the unstable pre-cooling and dehydration effect directly affects the safe operation of the cryogenic system. One of the core purposes of pre-cooling is to reduce the temperature of the oil and gas to about 1°C and remove as much water vapor as possible. If the oil and gas temperature is too high after pre-cooling and the residual water content is too high, the water vapor will freeze on the surface of the heat exchanger to form frost during the subsequent cryogenic process, which will lead to a decrease in heat exchange efficiency. In severe cases, the heat exchanger equipment may be damaged due to the ice expansion effect, or even a safety accident may occur.

[0006] Third, some improvement solutions still have limitations. To solve the above problems, some manufacturers have added a first-stage refrigerant direct heat exchanger after precooling in an attempt to stabilize the oil and gas temperature at around 1°C. However, this solution has the following defects: (1) The temperature fluctuation of the refrigerant direct heat exchanger is still large, and the oil and gas outlet temperature can deviate by up to 10°C, making it difficult to control precisely. (2) When the oil and gas volume deviates significantly from the design value, especially when the volume decreases significantly, the refrigeration compressor will frequently start and stop or fail to operate normally due to insufficient load, resulting in poor system stability.

[0007] Fourth, the recovery and utilization of cold energy from low-temperature lean oil gas is insufficient. In traditional systems, the cold energy of lean oil gas at approximately -70°C after cryogenic cooling is only recovered through a gas-to-gas heat exchanger. Due to limitations in heat exchange area and efficiency, the cold energy recovery rate is limited, resulting in low overall system energy efficiency.

[0008] In addition, according to Article 5.5.11 of GB / T50759-2022 "Technical Standard for Oil and Gas Recovery and Treatment Facilities", systems using cryogenic condensation technology must be equipped with a full-throughput backup channel (i.e., dual-channel design) to ensure continuous and reliable operation of the system during the defrosting and refreezing process of the heat exchanger. Summary of the Invention

[0009] The purpose of this invention is to provide an oil and gas condensation recovery system and method for refrigerant precooling and cascade recovery of cooling capacity, aiming to solve the problems of inaccurate temperature control, unstable dehydration, frosting and blockage, low cooling capacity utilization, and inability to operate continuously in the existing technology.

[0010] The present invention is an oil and gas condensation recovery system that achieves refrigerant precooling and cascade recovery of cold energy, comprising a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system, a liquid hydrocarbon recovery unit, an exhaust gas treatment unit, and an automatic control unit. The refrigerant precooling unit includes a precooling heat exchanger, which has an oil and gas side channel and a refrigerant side channel. The inlet of the oil and gas side channel is used to connect to the oil and gas to be processed, and the outlet of the oil and gas side channel is connected to the inlet of the cryogenic liquefaction unit. The cryogenic liquefaction unit includes a primary cryogenic heat exchanger and a secondary cryogenic heat exchanger arranged sequentially along the oil and gas flow direction; the primary and secondary cryogenic heat exchangers are respectively connected to an independent cascade refrigeration compressor unit, which provides cooling capacity; the inlet of the primary cryogenic heat exchanger is connected to the oil and gas side channel outlet of the precooling heat exchanger, the outlet of the primary cryogenic heat exchanger is connected to the inlet of the secondary cryogenic heat exchanger, and the outlet of the secondary cryogenic heat exchanger is connected to the lean oil and gas side channel inlet of the cooling capacity recovery heat exchanger; Both the primary cryogenic heat exchanger and the secondary cryogenic heat exchanger adopt a dual-channel structure, which includes a first channel and a second channel. The first channel and the second channel operate alternately. When the operating channel is used for oil and gas condensation, the standby channel uses the high-temperature refrigerant discharged from the cascade refrigeration compressor unit for defrosting. The cold energy recovery unit includes a cold energy recovery heat exchanger, which has a lean oil gas side channel and a refrigerant side channel. The inlet of the lean oil gas side channel is connected to the outlet of the cryogenic liquefaction unit, and the outlet of the lean oil gas side channel is connected to the exhaust gas treatment unit. The refrigerant circulation system includes a refrigerant tank, a refrigerant refrigeration unit, a refrigerant heat exchanger, a refrigerant circulation pump, and circulation pipelines. The circulation pipelines sequentially connect the outlet of the refrigerant tank, the refrigerant circulation pump, the refrigerant-side channel of the pre-cooling heat exchanger, the refrigerant-side channel of the cold energy recovery heat exchanger, the refrigerant heat exchanger, and the inlet of the refrigerant tank, forming a closed-loop circulation circuit. The refrigerant heat exchanger is connected to the refrigerant refrigeration unit, which provides it with cooling capacity. The refrigerant tank is equipped with an anti-foaming mechanism. The liquid hydrocarbon recovery unit is connected to the condensate outlet of the precooling heat exchanger and each stage of cryogenic heat exchanger, and is used to collect condensed liquid hydrocarbons. The automatic control unit is electrically connected to the refrigerant refrigeration unit, the cascade refrigeration compressor unit, the refrigerant circulation pump, and each valve to achieve automatic control.

[0011] Furthermore, the oil and gas outlet temperature of the precooling heat exchanger is -2℃ to 4℃; the outlet temperature of the first-stage cryogenic heat exchanger is -20℃ to -40℃; and the outlet temperature of the second-stage cryogenic heat exchanger is -65℃ to -75℃.

[0012] Furthermore, the refrigerant temperature in the refrigerant circulation system is set to -3℃ to -10℃; the oil and gas outlet temperature fluctuation range of the precooling heat exchanger is controlled within ±3℃.

[0013] Furthermore, oil and gas switching valves are respectively installed at the oil and gas inlet and oil and gas outlet of the first channel and the second channel, and the two channels are switched alternately by opening and closing the oil and gas switching valves. The first and second channels of the dual-channel structure are each independently equipped with a refrigerant supply valve, a refrigerant return valve, a defrost gas inlet valve, and a defrost liquid outlet valve. The refrigerant supply valve and refrigerant return valve of the operating channel are open, and the defrost gas inlet valve and defrost liquid outlet valve are closed. The refrigerant supply valve and refrigerant return valve of the backup channel are closed, while the defrost gas inlet valve and defrost liquid outlet valve are open. The high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit enters the backup channel through the defrost gas inlet valve for defrosting.

[0014] Furthermore, the dual-channel structure also includes a frosting detection device, which includes a differential pressure sensor and a temperature sensor; the differential pressure sensor and the temperature sensor are respectively installed at the oil and gas inlet and outlet positions of each channel and are electrically connected to the automatic control unit. When the frost detection device detects that the degree of frost on the operating channel reaches a preset threshold, the automatic control unit automatically performs channel switching, switching the operating channel to defrosting mode and switching the standby channel that has completed defrosting to operating mode.

[0015] Furthermore, the liquid hydrocarbon recovery unit includes a collection tank; the bottom of the precooling heat exchanger, the first-stage cryogenic heat exchanger, and the second-stage cryogenic heat exchanger are respectively provided with condensate outlets, and each condensate outlet is connected to the collection tank through a condensate discharge valve.

[0016] Furthermore, the exhaust gas treatment unit includes at least two alternately operating activated carbon adsorption tanks or resin adsorption tanks, with the two adsorption tanks alternately performing adsorption and desorption operations, and the inlet of the exhaust gas treatment unit is connected to the lean oil gas side channel outlet of the cold energy recovery heat exchanger.

[0017] Furthermore, the interior of the refrigerant tank is divided into an upper swirling chamber and a lower liquid storage chamber by a partition; the swirling chamber is located at the upper part of the refrigerant tank, and the liquid storage chamber is located directly below the swirling chamber; the defoaming mechanism includes a tangential liquid inlet pipe, an overflow partition, a defoaming cone, and a flow stabilizing guide plate; The refrigerant outlet of the circulation pipeline is tangentially connected to the swirling chamber through the tangential inlet pipe along the inner wall of the refrigerant tank. The refrigerant swirls at high speed along the cavity wall of the swirling chamber to form a swirling field. The foam gathers towards the center and bursts under the action of centrifugal force. The defoaming cone is located at the bottom of the swirling chamber, and the overflow baffle is installed on the top periphery of the defoaming cone. The defoaming cone has a top-opening guide channel, and the swirling chamber and the liquid storage chamber are connected through the guide channel. The flow stabilizing guide plate is inclinedly located below the outlet of the guide channel and extends to the bottom of the liquid storage chamber. After defoaming, the refrigerant flows over the overflow baffle, flows out through the guide channel, and then flows smoothly into the bottom of the liquid storage chamber along the flow stabilizing guide plate. The bottom of the liquid storage chamber has the outlet of the refrigerant tank and is connected to the inlet of the refrigerant circulation pump, ensuring that the refrigerant flows steadily in the liquid storage chamber before entering the circulation pipeline.

[0018] Furthermore, the defoaming mechanism also includes a microporous defoaming plate and a low-frequency acoustic wave vibrator. The low-frequency acoustic wave vibrator is fixedly installed on the top wall of the vortex chamber. The microporous defoaming plate is located above the overflow baffle. The low-frequency acoustic wave vibrator is fixed to the top of the microporous defoaming plate and electrically connected to the automatic control unit. The low-frequency acoustic wave vibrator, through low-frequency vibration combined with the microporous shearing action of the microporous defoaming plate, causes the rising foam to break down rapidly.

[0019] Compared with existing technologies, the oil and gas condensation recovery system with refrigerant precooling and cascaded cold energy recovery provided by this invention achieves fully automated processing of oil and gas from precooling, cryogenic liquefaction, cold energy recovery to tail gas treatment through the integrated design of a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system, a liquid hydrocarbon recovery unit, a tail gas treatment unit, and an automatic control unit. This covers the entire oil and gas recovery process without interruption. The precooling heat exchanger adopts an indirect heat exchange mode between oil and gas and the refrigerant, eliminating the dependence on cold energy from traditional lean oil and gas systems, avoiding precooling failure caused by ambient temperature fluctuations, stably removing water vapor and heavy hydrocarbons from the oil and gas, and preventing subsequent cryogenic frosting and blockage. Cold energy recovery... The heat exchanger transfers the low-temperature lean oil gas cooling capacity after cryogenic cooling to the refrigerant. The refrigerant circulation is a pre-cooling cooling system, achieving cascade utilization of cooling capacity from cryogenic to pre-cooling, reducing the energy consumption of the refrigerant refrigeration unit and improving the overall energy efficiency ratio of the system. The refrigerant circulation is a closed loop, with low cooling capacity loss and stable heat exchange, while avoiding refrigerant contamination and leakage, improving system safety and service life. The closed refrigerant circulation loop, together with the refrigerant water tank defoaming mechanism, prevents foam from being generated during the refrigerant circulation process, which may affect heat exchange and pump operation, ensuring the long-term stability of the circulation system. The automatic control unit links all equipment and valves to achieve fully automatic operation of temperature control, switching, and defrosting, reducing manual intervention and improving system reliability.

[0020] The oil and gas condensation recovery method for refrigerant precooling and cascade recovery of cooling capacity provided by this invention includes the following steps: S1) Refrigerant pre-cooling and dehydration step: The oil and gas to be treated are introduced into the pre-cooling heat exchanger. The oil and gas are indirectly pre-cooled by the refrigerant in the refrigerant circulation system with a temperature set at -3℃ to -10℃, so that the oil and gas temperature is stably reduced to the pre-cooling target temperature of -2℃ to 4℃. Most of the water vapor and heavy hydrocarbon components in the oil and gas are condensed and removed. The condensate is collected into the liquid hydrocarbon recovery unit through the bottom outlet of the pre-cooling heat exchanger. S2) Multi-stage cryogenic liquefaction step: The oil and gas, after pre-cooling and dehydration in step S1), are sequentially fed into the first-stage cryogenic heat exchanger and the second-stage cryogenic heat exchanger. The refrigerant provided by the cascade refrigeration compressor unit directly evaporates and exchanges heat, gradually cooling the oil and gas to an intermediate condensation temperature of -20℃ to -40℃ and a cryogenic target temperature of -65℃ to -75℃. The liquid hydrocarbon components condensed at each stage are discharged into the liquid hydrocarbon recovery unit respectively. The first-stage cryogenic heat exchanger and the second-stage cryogenic heat exchanger adopt a dual-channel alternating operation mode. When the frost on the operating channel reaches the preset threshold, the automatic control unit performs channel switching, and the operating channel switches to defrosting mode, using the high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit to defrost. The standby channel that has been defrosted switches to operating mode to ensure that the system can continuously process oil and gas. S3) Cold energy cascade recovery step: The low-temperature lean oil gas after the cryogenic treatment in step S2) is introduced into the cold energy recovery heat exchanger and indirectly exchanges heat with the refrigerant in the refrigerant circulation system. After the low-temperature lean oil gas releases cold energy, its temperature rises. The refrigerant absorbs cold energy and cools down. The refrigerant after cold energy recovery is cooled to the set temperature by the refrigerant heat exchanger and then circulated back to the pre-cooling heat exchanger to provide cold energy for the pre-cooling of oil and gas, thus realizing efficient cascade recovery of cold energy. S4) Exhaust gas treatment steps: The lean oil gas whose temperature rises after cold recovery is sent to the exhaust gas treatment unit, where residual oil gas components are adsorbed by alternating activated carbon adsorption tanks or resin adsorption tanks, and discharged after treatment to meet the standards.

[0021] Compared with the prior art, the oil and gas condensation recovery method for refrigerant precooling and cascade recovery of cold energy provided by the present invention has clear process steps and strong operability: the four-step process of S1 precooling and dehydration, S2 multi-stage deep cooling, S3 cold energy recovery and S4 tail gas treatment has rigorous logic and is easy to implement in industrial and equipment debugging. Pre-cooling and dehydration process protects cryogenic systems: It removes water vapor and heavy hydrocarbons first, preventing frost and ice buildup on cryogenic heat exchangers from the source, extending equipment lifespan and reducing maintenance costs. Dual-channel defrosting integration ensures continuous operation: The cryogenic process integrates channel switching and defrosting logic synchronously, solving the industry pain point of defrosting shutdown in traditional condensation processes; The cold energy is cascaded and closed-loop, resulting in significant energy-saving benefits: all the cold energy of the low-temperature lean oil gas is recovered and used for pre-cooling, reducing the cooling capacity requirement of the refrigerant refrigeration unit and lowering the overall power consumption of the system; Deep exhaust gas treatment, environmentally compliant: The combined process of condensation and adsorption far exceeds the treatment effect of single condensation method, ensuring that oil and gas emissions meet the national VOCs treatment standards. Attached Figure Description

[0022] Figure 1 This is a schematic flowchart of the oil and gas condensation recovery method for refrigerant precooling and cascade recovery of cooling capacity provided by the present invention. Figure 2 This is a schematic diagram of the structural layout of the oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity provided by the present invention; Figure 3 This is a cross-sectional structural diagram of the coolant tank provided by the present invention.

[0023] In the diagram: Precooling heat exchanger 10, primary cryogenic heat exchanger 20, secondary cryogenic heat exchanger 30, cascade refrigeration compressor unit 40, cold energy recovery heat exchanger 50, refrigerant circulation system 60, oil-gas side channel 11, refrigerant side channel 12, lean oil-gas side channel 51, refrigerant side channel 52, refrigerant water tank 61, refrigerant refrigeration unit 62, refrigerant heat exchanger 63, refrigerant circulation pump 64, circulation pipeline 65, swirl chamber 611, liquid storage chamber 612, tangential liquid inlet pipe 613, overflow baffle 614, defoaming cone 615, flow guide channel 616, flow stabilizing guide plate 617, low-frequency acoustic wave vibrator 618, microporous defoaming plate 619. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] The implementation of the present invention will be described in detail below with reference to specific embodiments.

[0026] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this invention, it should be understood that if terms such as "upper," "lower," "left," and "right" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] Reference Figure 1-3 The image shows a preferred embodiment of the present invention.

[0028] The oil and gas condensation recovery system with refrigerant precooling and cold energy cascade recovery includes a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system 60, a liquid hydrocarbon recovery unit, a tail gas treatment unit, and an automatic control unit; The refrigerant precooling unit includes a precooling heat exchanger 10, which has an oil and gas side channel 11 and a refrigerant side channel 12. The inlet of the oil and gas side channel 11 is used to connect the oil and gas to be processed, and the outlet of the oil and gas side channel 11 is connected to the inlet of the cryogenic liquefaction unit. The cryogenic liquefaction unit includes a primary cryogenic heat exchanger 20 and a secondary cryogenic heat exchanger 30 arranged sequentially along the oil and gas flow direction; the primary cryogenic heat exchanger 20 and the secondary cryogenic heat exchanger 30 are respectively connected to an independent cascade refrigeration compressor unit 40, which provides cooling capacity; the inlet of the primary cryogenic heat exchanger 20 is connected to the outlet of the oil and gas side passage 11 of the precooling heat exchanger 10, the outlet of the primary cryogenic heat exchanger 20 is connected to the inlet of the secondary cryogenic heat exchanger 30, and the outlet of the secondary cryogenic heat exchanger 30 is connected to the inlet of the lean oil and gas side passage 51 of the cooling capacity recovery heat exchanger 50; Both the primary cryogenic heat exchanger 20 and the secondary cryogenic heat exchanger 30 adopt a dual-channel structure, which includes a first channel and a second channel. The first channel and the second channel operate alternately. When the operating channel is used for oil and gas condensation, the standby channel uses the high-temperature refrigerant discharged from the cascade refrigeration compressor unit 40 for defrosting. The cold energy recovery unit includes a cold energy recovery heat exchanger 50, which has a lean oil gas side channel 51 and a refrigerant side channel 52. The inlet of the lean oil gas side channel 51 is connected to the outlet of the cryogenic liquefaction unit, and the outlet of the lean oil gas side channel 51 is connected to the exhaust gas treatment unit. The refrigerant circulation system 60 includes a refrigerant tank 61, a refrigerant refrigeration unit 62, a refrigerant heat exchanger 63, a refrigerant circulation pump 64, and a circulation pipeline 65. The circulation pipeline 65 sequentially connects the outlet of the refrigerant tank 61, the refrigerant circulation pump 64, the refrigerant-side channel 12 of the pre-cooling heat exchanger 10, the refrigerant-side channel 52 of the cold energy recovery heat exchanger 50, the refrigerant heat exchanger 63, and the inlet of the refrigerant tank 61, forming a closed-loop circulation circuit. The refrigerant heat exchanger 63 is connected to the refrigerant refrigeration unit 62, which provides it with cooling capacity. The refrigerant tank 61 is equipped with an anti-foaming mechanism. The liquid hydrocarbon recovery unit is connected to the condensate outlet of the precooling heat exchanger 10 and each stage of cryogenic heat exchangers, and is used to collect condensed liquid hydrocarbons. The automatic control unit is electrically connected to the refrigerant refrigeration unit 62, the cascade refrigeration compressor unit 40, the refrigerant circulation pump 64, and each valve to achieve automatic control.

[0029] The aforementioned oil and gas condensation recovery system, featuring refrigerant precooling and cascaded cold energy recovery, achieves fully automated processing of oil and gas from precooling, cryogenic liquefaction, cold energy recovery, refrigerant circulation system 60, liquid hydrocarbon recovery unit, tail gas treatment unit, and automatic control unit. This is achieved through the integrated design of a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system 60, a liquid hydrocarbon recovery unit, a tail gas treatment unit, and an automatic control unit. It covers the entire oil and gas recovery process without interruption. The precooling heat exchanger 10 employs an indirect heat exchange mode between oil / gas and refrigerant, eliminating reliance on traditional lean oil / gas cold energy and preventing precooling failure due to ambient temperature fluctuations. This ensures stable removal of water vapor and heavy hydrocarbons from the oil / gas, preventing subsequent cryogenic frosting and blockage. The cold energy recovery heat exchanger 50... After cryogenic cooling, the low-temperature lean oil gas's cooling capacity is transferred to the refrigerant. The refrigerant circulation is a pre-cooling cooling system, achieving cascade utilization of cooling capacity from cryogenic to pre-cooling, reducing the energy consumption of the refrigerant refrigeration unit 62, and improving the overall system energy efficiency ratio. The refrigerant circulation is a closed loop, resulting in low cooling capacity loss and stable heat exchange, while avoiding refrigerant contamination and leakage, thus improving system safety and service life. The closed refrigerant circulation loop, combined with the refrigerant water tank 61's defoaming mechanism, prevents foam generation during refrigerant circulation from affecting heat exchange and pump operation, ensuring long-term stability of the circulation system. The automatic control unit links all equipment and valves to achieve fully automatic operation of temperature control, switching, and defrosting, reducing manual intervention and improving system reliability.

[0030] The refrigerant circulation system 60 and the cryogenic refrigeration system operate independently and do not interfere with each other, which reduces the risk of overall system failure and improves the reliability and ease of maintenance in long-term operation.

[0031] The primary cryogenic heat exchanger 20 and the secondary cryogenic heat exchanger 30 adopt a dual-channel structure, with condensation in the operating channel and defrosting in the standby channel occurring simultaneously. Combined with the high-temperature refrigerant defrosting of the cascade refrigeration compressor unit 40 itself, no additional heat source is required, meeting the full-flow standby requirements of GB / T50759-2022 and ensuring the system can continuously process oil and gas 24 hours a day.

[0032] The condensate from precooling and deep cooling at each stage is uniformly collected into the liquid hydrocarbon recovery unit, maximizing the recovery of hydrocarbon components in oil and gas, thus achieving both environmental and economic benefits.

[0033] As an extended embodiment, the oil and gas outlet temperature of the precooling heat exchanger 10 is -2℃ to 4℃; the outlet temperature of the first-stage cryogenic heat exchanger 20 is -20℃ to -40℃; and the outlet temperature of the second-stage cryogenic heat exchanger 30 is -65℃ to -75℃.

[0034] The precooling section features precise temperature control from -2℃ to -4℃, efficiently dehydrating hydrocarbons and preventing icing and blockage, thus creating stable inlet conditions for the cryogenic section. The first-stage cryogenic heat exchanger condenses and separates medium and heavy hydrocarbons at 20-20℃ to -40℃, while the second-stage cryogenic heat exchanger deeply liquefies light hydrocarbons at 30-65℃ to -75℃. This step-by-step condensation process improves hydrocarbon recovery. The temperature range is matched to the hydrocarbon dew point distribution, achieving an optimal balance between high recovery rate and low energy consumption.

[0035] As an extended embodiment, the refrigerant temperature in the refrigerant circulation system 60 is set to -3℃ to -10℃; the oil and gas outlet temperature fluctuation range of the precooling heat exchanger 10 is controlled within ±3℃.

[0036] The refrigerant is stably supplied at -3℃ to -10℃, providing a sufficient and controllable source of cooling for oil and gas precooling; the oil and gas outlet temperature fluctuation is ≤±3℃, and the temperature control accuracy is improved compared with the traditional direct cooling solution (±10℃), and the dehydration effect is stable and reliable; the temperature fluctuation is small, avoiding uneven frosting and efficiency reduction in the deep cryogenic section due to sudden load changes.

[0037] As an extended embodiment, oil and gas switching valves are respectively installed at the oil and gas inlet and oil and gas outlet of the first channel and the second channel, and the two channels are switched alternately by opening and closing the oil and gas switching valves. The first and second channels of the dual-channel structure are each independently equipped with a refrigerant liquid supply valve, a refrigerant return gas valve, a defrost gas inlet valve, and a defrost liquid outlet valve. The refrigerant supply valve and refrigerant return valve in the operating channel are open, while the defrost gas inlet valve and defrost liquid outlet valve are closed. The refrigerant supply valve and refrigerant return valve of the standby passage are closed, while the defrost gas inlet valve and defrost liquid outlet valve are opened. The high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit 40 enters the standby passage through the defrost gas inlet valve for defrosting.

[0038] Convenient channel switching and high degree of automation: The oil-gas switching valve independently controls the on / off of the two channels, with fast switching response and no need for manual intervention, ensuring continuous and uninterrupted oil-gas processing; Independent valve configuration and clear operating modes: The operating channel opens the refrigerant supply and return liquid valves and closes the defrost gas inlet valve and defrost liquid outlet valve, focusing on condensation heat exchange; The standby channel closes the refrigerant supply liquid valve and refrigerant return gas valve, using the high-temperature gas from the compressor for defrosting, and the mode switching is interference-free.

[0039] The defrosting heat source is self-sufficient, saving energy and reducing consumption: the high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit 40 is directly reused for defrosting, without the need for external heat sources such as steam or electric heating, thus reducing system energy consumption and operating costs.

[0040] As an extended embodiment, the dual-channel structure also includes a frosting detection device, which includes a differential pressure sensor and a temperature sensor; the differential pressure sensor and the temperature sensor are respectively installed at the oil and gas inlet and outlet positions of each channel and are electrically connected to the automatic control unit. When the frost detection device detects that the degree of frost on the operating channel has reached a preset threshold, the automatic control unit automatically performs channel switching, switching the operating channel to defrosting mode and switching the standby channel that has completed defrosting to operating mode.

[0041] Accurate frost detection and reasonable switching timing: Differential pressure and temperature sensors monitor the degree of frost in the channel in real time, and the data is synchronously transmitted to the automatic control unit to avoid excessive frost affecting heat exchange or premature switching that wastes energy.

[0042] Intelligent automatic switching, unattended operation: When the preset frost threshold is reached, the channel is automatically switched without manual operation, which improves the intelligence level of the system and is suitable for long-term continuous operation scenarios.

[0043] As an extended embodiment, the liquid hydrocarbon recovery unit includes a collection tank; the bottom of the precooling heat exchanger 10, the first-stage cryogenic heat exchanger 20, and the second-stage cryogenic heat exchanger 30 are respectively provided with condensate outlets, and each condensate outlet is connected to the collection tank through a condensate discharge valve.

[0044] Condensate collection is smooth and there is no risk of leakage: The precooling heat exchanger 10, the first-stage cryogenic heat exchanger 20, and the second-stage cryogenic heat exchanger 30 are equipped with condensate outlets at the bottom. The condensate is collected into the collection tank through the discharge valve and flows by gravity. The pipeline resistance is small and the recovery efficiency is high.

[0045] Unified storage management facilitates subsequent utilization: Centralized storage of liquid hydrocarbons facilitates measurement, transfer and reuse, realizing closed-loop recovery of oil and gas resources.

[0046] As an extended embodiment, the exhaust gas treatment unit includes at least two alternately operating activated carbon adsorption tanks or resin adsorption tanks, with the two adsorption tanks alternately performing adsorption and desorption operations, and the inlet of the exhaust gas treatment unit is connected to the outlet of the lean oil gas side channel 51 of the cold energy recovery heat exchanger 50.

[0047] The adsorption units operate alternately, ensuring continuous treatment: the two adsorption tanks alternately adsorb and desorb, avoiding excessive exhaust gas emissions after a single tank becomes saturated, and ensuring uninterrupted exhaust gas treatment.

[0048] Reliable adsorption effect and emission compliance: Activated carbon / resin adsorption tanks specifically adsorb residual trace oil and gas components, deeply purify exhaust gas, and meet environmental emission limits.

[0049] As an extended embodiment, the interior of the refrigerant tank 61 is divided into an upper swirling chamber 611 and a lower liquid storage chamber 612 by a partition; the swirling chamber 611 is located at the upper part of the refrigerant tank 61, and the liquid storage chamber 612 is located directly below the swirling chamber 611; the defoaming mechanism includes a tangential liquid inlet pipe 613, an overflow partition 614, a defoaming cone 615, and a flow stabilizing guide plate 617; The refrigerant outlet of the circulation pipeline 65 is tangentially connected to the vortex chamber 611 through the tangential liquid inlet pipe 613 along the inner wall of the refrigerant tank 61. The refrigerant swirls at high speed along the cavity wall of the vortex chamber 611 to form a vortex field. The foam gathers towards the center and bursts under the action of centrifugal force. A defoaming cone 615 is disposed at the bottom of the swirling chamber 611, and an overflow baffle 614 is installed on the top periphery of the defoaming cone 615. The defoaming cone 615 is provided with a top-opening guide channel 616. The swirling chamber 611 and the liquid storage chamber 612 are connected through the guide channel 616. A flow stabilizing guide plate 617 is inclinedly disposed below the outlet of the guide channel 616 and extends to the bottom of the liquid storage chamber 612. After defoaming, the refrigerant flows over the overflow baffle 614, flows out through the guide channel 616, and then flows smoothly into the bottom of the liquid storage chamber 612 along the flow stabilizing guide plate 617. The bottom of the liquid storage chamber 612 has an outlet for the refrigerant tank 61 and is connected to the inlet of the refrigerant circulation pump 64, ensuring that the refrigerant enters the circulation pipeline 65 after being fully stabilized in the liquid storage chamber 612.

[0050] The inner wall of the swirl chamber 611 is machined with spiral grooves, which are arranged vertically from top to bottom along the chamber to enhance the swirl and defoaming effects.

[0051] Tangential liquid inlet creates a swirling flow field, and the foam gathers and bursts towards the center under the action of centrifugal force, eliminating the need for chemical defoamers, avoiding refrigerant pollution, and making it environmentally friendly and safe.

[0052] The defoaming cone 615 and the flow stabilizing guide plate 617 guide the refrigerant to flow smoothly into the liquid storage chamber 612, avoiding turbulence and secondary foaming, ensuring stable intake of the refrigerant circulation pump 64, and eliminating the risk of cavitation.

[0053] The cavity is rationally divided, with liquid storage and defoaming separated: the upper vortex cavity 611 focuses on defoaming, while the lower liquid storage cavity 612 is responsible for stabilizing the flow and storing liquid. The functional zoning is clear, which improves the overall effect of defoaming and circulation.

[0054] As an extended embodiment, the defoaming mechanism also includes a microporous defoaming plate 619 and a low-frequency acoustic wave vibrator 618. The low-frequency acoustic wave vibrator 618 is fixedly installed on the top wall of the swirling cavity 611. The microporous defoaming plate 619 is located above the overflow baffle 614. The low-frequency acoustic wave vibrator 618 is fixed to the top of the microporous defoaming plate 619 and is electrically connected to the automatic control unit. The low-frequency acoustic wave vibrator 618, through low-frequency vibration in conjunction with the microporous shearing action of the microporous defoaming plate 619, causes the rising foam to break down rapidly.

[0055] Composite defoaming completely eliminates foam: The vibration of the low-frequency acoustic oscillator 618, combined with the shearing action of the microporous defoaming plate 619, further breaks down the residual foam that has not broken in the swirling flow, improving the defoaming efficiency by several times compared to a single swirling flow.

[0056] Intelligent linkage control, defoaming on demand: The low-frequency acoustic wave vibrator 618 is electrically connected to the automatic control unit and can start and stop according to the amount of foam in the refrigerant, saving energy and extending the service life of the equipment.

[0057] The oil and gas condensation recovery method for refrigerant precooling and cascade recovery of cooling capacity provided by this invention includes the following steps: S1) Refrigerant pre-cooling and dehydration step: The oil and gas to be treated are introduced into the pre-cooling heat exchanger 10. The oil and gas are indirectly pre-cooled by the refrigerant in the refrigerant circulation system 60 with the temperature set at -3℃ to -10℃, so that the temperature of the oil and gas is stably reduced to the pre-cooling target temperature of -2℃ to 4℃. Most of the water vapor and heavy hydrocarbon components in the oil and gas are condensed and removed. The condensate is collected into the liquid hydrocarbon recovery unit through the bottom outlet of the pre-cooling heat exchanger 10. S2) Multi-stage cryogenic liquefaction step: The oil and gas, after pre-cooling and dehydration in step S1), are sequentially fed into the first-stage cryogenic heat exchanger 20 and the second-stage cryogenic heat exchanger 30. The refrigerant provided by the cascade refrigeration compressor unit 40 directly evaporates and exchanges heat, gradually cooling the oil and gas to an intermediate condensation temperature of -20℃ to -40℃ and a cryogenic target temperature of -65℃ to -75℃. The liquid hydrocarbon components condensed at each stage are discharged into the liquid hydrocarbon recovery unit respectively. The first-stage cryogenic heat exchanger 20 and the second-stage cryogenic heat exchanger 30 adopt a dual-channel alternating operation mode. When the frost on the operating channel reaches the preset threshold, the automatic control unit performs channel switching, and the operating channel switches to defrosting mode. The high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit 40 is used for defrosting. The standby channel that has been defrosted switches to operating mode to ensure that the system can continuously process oil and gas. S3) Cold energy cascade recovery step: The low-temperature lean oil gas after the cryogenic treatment in step S2) is introduced into the cold energy recovery heat exchanger 50 and indirectly exchanges heat with the refrigerant in the refrigerant circulation system 60. After the low-temperature lean oil gas releases cold energy, its temperature rises. The refrigerant absorbs cold energy and cools down. The refrigerant after cold energy recovery is cooled to the set temperature by the refrigerant heat exchanger 63 and circulated back to the pre-cooling heat exchanger 10 to provide cold energy for oil and gas pre-cooling, thus realizing efficient cascade recovery of cold energy. S4) Exhaust gas treatment steps: The lean oil gas whose temperature rises after cold recovery is sent to the exhaust gas treatment unit, where residual oil gas components are adsorbed by alternating activated carbon adsorption tanks or resin adsorption tanks, and discharged after treatment to meet the standards.

[0058] The above-mentioned method for oil and gas condensation recovery through refrigerant precooling and cascade recovery of cooling capacity is described below. The process steps are clear and highly operable: the four-step process of S1 pre-cooling and dehydration, S2 multi-stage deep cooling, S3 cold energy recovery, and S4 exhaust gas treatment has a rigorous logic and is easy to implement industrially and debug equipment. Pre-cooling and dehydration process protects cryogenic systems: It removes water vapor and heavy hydrocarbons first, preventing frost and ice buildup on cryogenic heat exchangers from the source, extending equipment lifespan and reducing maintenance costs. Dual-channel defrosting integration ensures continuous operation: The cryogenic process integrates channel switching and defrosting logic synchronously, solving the industry pain point of defrosting shutdown in traditional condensation processes; The cold energy is cascaded and closed-loop, resulting in significant energy-saving benefits: all the cold energy of the low-temperature lean oil gas is recovered and used for pre-cooling, reducing the cooling capacity requirement of the refrigerant chiller unit 62 and reducing the overall power consumption of the system. Deep exhaust gas treatment, environmentally compliant: The combined process of condensation and adsorption far exceeds the treatment effect of single condensation method, ensuring that oil and gas emissions meet the national VOCs treatment standards.

[0059] The refrigerant in the refrigerant circulation system 60 is one of ethylene glycol aqueous solution, propylene glycol aqueous solution, or dichloromethane. Ethylene glycol / propylene glycol aqueous solution is non-toxic, non-corrosive, and non-flammable, suitable for food-grade and industrial-grade oil and gas treatment scenarios, and has high safety. The selected refrigerant maintains good fluidity below -10℃, has high heat exchange efficiency, and meets the low-temperature requirements for pre-cooling and cold energy recovery.

[0060] All control valves in the system are either electric or pneumatic, and all valves are controlled by an automatic control unit.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An oil-gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity, characterized in that, It includes a refrigerant precooling unit, a cryogenic liquefaction unit, a cold energy recovery unit, a refrigerant circulation system, a liquid hydrocarbon recovery unit, an exhaust gas treatment unit, and an automatic control unit; The refrigerant precooling unit includes a precooling heat exchanger, which has an oil and gas side channel and a refrigerant side channel. The inlet of the oil and gas side channel is used to connect to the oil and gas to be processed, and the outlet of the oil and gas side channel is connected to the inlet of the cryogenic liquefaction unit. The cryogenic liquefaction unit includes a primary cryogenic heat exchanger and a secondary cryogenic heat exchanger arranged sequentially along the oil and gas flow direction; the primary and secondary cryogenic heat exchangers are respectively connected to an independent cascade refrigeration compressor unit, which provides cooling capacity; the inlet of the primary cryogenic heat exchanger is connected to the oil and gas side channel outlet of the precooling heat exchanger, the outlet of the primary cryogenic heat exchanger is connected to the inlet of the secondary cryogenic heat exchanger, and the outlet of the secondary cryogenic heat exchanger is connected to the lean oil and gas side channel inlet of the cooling capacity recovery heat exchanger; Both the primary cryogenic heat exchanger and the secondary cryogenic heat exchanger adopt a dual-channel structure, which includes a first channel and a second channel. The first channel and the second channel operate alternately. When the operating channel is used for oil and gas condensation, the standby channel uses the high-temperature refrigerant discharged from the cascade refrigeration compressor unit for defrosting. The cold energy recovery unit includes a cold energy recovery heat exchanger, which has a lean oil gas side channel and a refrigerant side channel. The inlet of the lean oil gas side channel is connected to the outlet of the cryogenic liquefaction unit, and the outlet of the lean oil gas side channel is connected to the exhaust gas treatment unit. The refrigerant circulation system includes a refrigerant tank, a refrigerant refrigeration unit, a refrigerant heat exchanger, a refrigerant circulation pump, and circulation pipelines. The circulation pipelines sequentially connect the outlet of the refrigerant tank, the refrigerant circulation pump, the refrigerant-side channel of the pre-cooling heat exchanger, the refrigerant-side channel of the cold energy recovery heat exchanger, the refrigerant heat exchanger, and the inlet of the refrigerant tank, forming a closed-loop circulation circuit. The refrigerant heat exchanger is connected to the refrigerant refrigeration unit, which provides it with cooling capacity. The refrigerant tank is equipped with an anti-foaming mechanism. The liquid hydrocarbon recovery unit is connected to the condensate outlet of the precooling heat exchanger and each stage of cryogenic heat exchanger, and is used to collect condensed liquid hydrocarbons. The automatic control unit is electrically connected to the refrigerant refrigeration unit, the cascade refrigeration compressor unit, the refrigerant circulation pump, and each valve to achieve automatic control.

2. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 1, characterized in that, The oil and gas outlet temperature of the precooling heat exchanger is -2℃ to 4℃; the outlet temperature of the first-stage cryogenic heat exchanger is -20℃ to -40℃; and the outlet temperature of the second-stage cryogenic heat exchanger is -65℃ to -75℃.

3. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 1, characterized in that, The refrigerant temperature in the refrigerant circulation system is set to -3℃ to -10℃; the oil and gas outlet temperature fluctuation range of the precooling heat exchanger is controlled within ±3℃.

4. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 1, characterized in that, Both the first and second channels are equipped with oil and gas switching valves at their oil and gas inlets and outlets, and the two channels are switched alternately by opening and closing the oil and gas switching valves. The first and second channels of the dual-channel structure are each independently equipped with a refrigerant liquid supply valve, a refrigerant return gas valve, a defrost gas inlet valve, and a defrost liquid outlet valve. The refrigerant supply valve and refrigerant return valve of the operating channel are open, and the defrost gas inlet valve and defrost liquid outlet valve are closed. The refrigerant supply valve and refrigerant return valve of the backup channel are closed, while the defrost gas inlet valve and defrost liquid outlet valve are open. The high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit enters the backup channel through the defrost gas inlet valve for defrosting.

5. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 4, characterized in that, The dual-channel structure also includes a frosting detection device, which includes a differential pressure sensor and a temperature sensor. The differential pressure sensor and the temperature sensor are respectively installed at the oil and gas inlet and outlet positions of each channel and are electrically connected to the automatic control unit. When the frost detection device detects that the degree of frost on the operating channel reaches a preset threshold, the automatic control unit automatically performs channel switching, switching the operating channel to defrosting mode and switching the standby channel that has completed defrosting to operating mode.

6. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 1, characterized in that, The liquid hydrocarbon recovery unit includes a collection tank; the bottom of the precooling heat exchanger, the first-stage cryogenic heat exchanger, and the second-stage cryogenic heat exchanger are respectively provided with condensate outlets, and each condensate outlet is connected to the collection tank through a condensate discharge valve.

7. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 1, characterized in that, The exhaust gas treatment unit includes at least two alternately operating activated carbon adsorption tanks or resin adsorption tanks. The two adsorption tanks alternately perform adsorption and desorption operations, and the inlet of the exhaust gas treatment unit is connected to the lean oil gas side channel outlet of the cold energy recovery heat exchanger.

8. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in any one of claims 1 to 7, characterized in that, The interior of the refrigerant tank is divided into an upper swirling chamber and a lower liquid storage chamber by a partition; the swirling chamber is located at the upper part of the refrigerant tank, and the liquid storage chamber is located directly below the swirling chamber; the defoaming mechanism includes a tangential liquid inlet pipe, an overflow partition, a defoaming cone, and a flow stabilizing guide plate; The refrigerant outlet of the circulation pipeline is tangentially connected to the swirling chamber through the tangential inlet pipe along the inner wall of the refrigerant tank. The refrigerant swirls at high speed along the cavity wall of the swirling chamber to form a swirling field. The foam gathers towards the center and bursts under the action of centrifugal force. The defoaming cone is located at the bottom of the swirling chamber, and the overflow baffle is installed on the top periphery of the defoaming cone. The defoaming cone has a top-opening guide channel, and the swirling chamber and the liquid storage chamber are connected through the guide channel. The flow stabilizing guide plate is inclinedly located below the outlet of the guide channel and extends to the bottom of the liquid storage chamber. After defoaming, the refrigerant flows over the overflow baffle, flows out through the guide channel, and then flows smoothly into the bottom of the liquid storage chamber along the flow stabilizing guide plate. The bottom of the liquid storage chamber has the outlet of the refrigerant tank and is connected to the inlet of the refrigerant circulation pump, ensuring that the refrigerant flows steadily in the liquid storage chamber before entering the circulation pipeline.

9. The oil and gas condensation recovery system for refrigerant precooling and cascade recovery of cooling capacity as described in claim 8, characterized in that, The defoaming mechanism also includes a microporous defoaming plate and a low-frequency acoustic wave vibrator. The low-frequency acoustic wave vibrator is fixedly installed on the top wall of the vortex chamber. The microporous defoaming plate is located above the overflow baffle. The low-frequency acoustic wave vibrator is fixed on the top of the microporous defoaming plate and electrically connected to the automatic control unit. The low-frequency acoustic wave vibrator, through low-frequency vibration combined with the microporous shearing action of the microporous defoaming plate, causes the rising foam to break down rapidly.

10. The oil and gas condensation recovery method for precooling the refrigerant and recovering the cooling capacity in stages as described in any one of claims 1 to 9, characterized in that, Includes the following steps: S1) Refrigerant pre-cooling and dehydration step: The oil and gas to be treated are introduced into the pre-cooling heat exchanger. The oil and gas are indirectly pre-cooled by the refrigerant in the refrigerant circulation system with a temperature set at -3℃ to -10℃, so that the oil and gas temperature is stably reduced to the pre-cooling target temperature of -2℃ to 4℃. Most of the water vapor and heavy hydrocarbon components in the oil and gas are condensed and removed. The condensate is collected into the liquid hydrocarbon recovery unit through the bottom outlet of the pre-cooling heat exchanger. S2) Multi-stage cryogenic liquefaction step: The oil and gas, after pre-cooling and dehydration in step S1), are sequentially fed into the first-stage cryogenic heat exchanger and the second-stage cryogenic heat exchanger. The refrigerant provided by the cascade refrigeration compressor unit directly evaporates and exchanges heat, gradually cooling the oil and gas to an intermediate condensation temperature of -20℃ to -40℃ and a cryogenic target temperature of -65℃ to -75℃. The liquid hydrocarbon components condensed at each stage are discharged into the liquid hydrocarbon recovery unit respectively. The first-stage cryogenic heat exchanger and the second-stage cryogenic heat exchanger adopt a dual-channel alternating operation mode. When the frost on the operating channel reaches the preset threshold, the automatic control unit performs channel switching, and the operating channel switches to defrosting mode, using the high-temperature and high-pressure refrigerant gas discharged from the cascade refrigeration compressor unit to defrost. The standby channel that has been defrosted switches to operating mode to ensure that the system can continuously process oil and gas. S3) Cold energy cascade recovery step: The low-temperature lean oil gas after the cryogenic treatment in step S2) is introduced into the cold energy recovery heat exchanger and indirectly exchanges heat with the refrigerant in the refrigerant circulation system. After the low-temperature lean oil gas releases cold energy, its temperature rises. The refrigerant absorbs cold energy and cools down. The refrigerant after cold energy recovery is cooled to the set temperature by the refrigerant heat exchanger and then circulated back to the pre-cooling heat exchanger to provide cold energy for the pre-cooling of oil and gas, thus realizing efficient cascade recovery of cold energy. S4) Exhaust gas treatment steps: The lean oil gas whose temperature rises after cold recovery is sent to the exhaust gas treatment unit, where residual oil gas components are adsorbed by alternating activated carbon adsorption tanks or resin adsorption tanks, and discharged after treatment to meet the standards.

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