A low-pressure wellhead gas membrane separation and deep cooling combined decarburization and dealkylation recovery method

Abstract

This invention discloses a method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and dehydrocarbonization recovery, relating to the field of integrated natural gas processing technology. To address the problems of equipment corrosion and ice blockage, low gas-liquid combined yield, and environmental pollution from tail gas emissions in existing technologies, the following technical solution is proposed: including the following steps: S1, filtration and separation; S2, pressurization and compression; S3, membrane decarbonization; S4, dehydration; S5, cooling and separation; S6, dry gas output; S7, dehydrocarbonization and stabilization. This invention features a simple process flow, low energy consumption, high product yield, and good load regulation capability and automation control level, making it suitable for the resource recovery and utilization of low-pressure, small-scale wellhead gas.

Description

Technical Field

[0001] This invention relates to the field of integrated natural gas processing technology, specifically to a method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery. Background Technology

[0002] During the oil and gas field development process, a large amount of wellhead gas (or associated gas) is usually generated. This type of low-pressure wellhead gas typically has an extremely low inlet pressure (only 0.1~0.25 MPaG) and a complex composition. In addition to methane, it contains a high proportion of C2+ (ethane and above) heavy hydrocarbon components, as well as water, carbon dioxide, and solid impurities.

[0003] In the past, due to low pressure, dispersed gas sources, and large fluctuations in production, this gas was often directly emitted through combustion without treatment. This not only resulted in a serious waste of fossil fuel resources but also caused significant greenhouse gas pollution to the surrounding environment. In recent years, with the promotion of energy conservation, emission reduction, and natural gas recovery technologies, purifying and pressurizing wellhead gas to produce compressed natural gas (CNG) and by-product mixed light hydrocarbons (NGL) has become the mainstream trend.

[0004] However, existing conventional processing techniques for recovering low-pressure wellhead gas face numerous technical bottlenecks. Firstly, pressurizing the purified gas to a high pressure of 22.0 MPaG for injection into CNG tankers places extremely high demands on the water and carbon dioxide content of the natural gas. If carbon dioxide removal is incomplete, it easily combines with trace amounts of moisture under high pressure to form carbonic acid, causing severe intergranular corrosion to the compressor and pipelines. Furthermore, traditional amine-based decarbonization processes involve large equipment and require significant heat energy for solution circulation, making them unsuitable for wellhead gas recovery sites where compact equipment (such as skid-mounted systems) is crucial.

[0005] Secondly, in order to achieve high-quality natural gas standards and extract high-value-added mixed hydrocarbons (NGLs), cryogenic processes are required to cool the gas to around -35°C to condense the C2+ components. However, if the dehydration depth at the front end is insufficient, residual moisture will form ice particles or natural gas hydrates in the cryogenic heat exchanger or cryogenic separator, which can lead to serious pipeline "ice blockage" accidents and force the system to shut down.

[0006] Furthermore, in traditional dehydration and dehydrocarbonization processes, the waste gas generated during the molecular sieve thermal regeneration cycle and the overhead gas phase from the light hydrocarbon stabilization tower distillation are typically vented directly as waste gas or burned as low-value fuel. This gas still contains a large amount of unrecovered effective hydrocarbon components. This open-loop process design not only leads to a decrease in overall hydrocarbon yield but also poses safety hazards.

[0007] Therefore, there is an urgent need in this field for a highly integrated processing method that can adapt to low-pressure and wide-load fluctuations. This method needs to organically combine membrane separation decarbonization technology with molecular sieve deep dehydration and cryogenic dehydrogenation technology, and recycle various intermediate tail gases through a closed-loop process path, thereby completely solving the common industry problems of difficult treatment of impurities in low-pressure wellhead gas, easy ice blockage in cryogenic processes, low hydrocarbon yield, and easy damage to equipment during high-pressure CNG preparation. Summary of the Invention

[0008] The purpose of this invention is to provide a method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and dehydrocarbonization recovery, so as to solve the problems of easy equipment corrosion and ice blockage, low gas-liquid comprehensive recovery rate and environmental pollution caused by tail gas emissions in the prior art.

[0009] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery includes the following steps: S1. Filtration and separation: The raw gas is passed into the inlet filter separator to separate and remove solid particles and tiny droplets from the raw gas, resulting in primary filtered gas and the first stream of oily wastewater. S2, Pressurization and Compression: The primary filtered gas is introduced into the feed gas compressor with frequency conversion control for pressurization; the aftercooling parameters of the feed gas compressor are adjusted by the control unit to control the exhaust temperature within the first preset temperature range, so as to obtain warm pressurized feed gas; S3, Membrane Decarbonization: Warm and pressurized feed gas is introduced into a membrane separation decarbonization skid equipped with an ultrasonic transducer matrix; the control unit collects the actual temperature of the feed gas in real time and compares it with the set reference temperature: when the actual temperature of the feed gas deviates from the reference temperature, the control unit controls the output power of the ultrasonic transducer matrix to increase or decrease in the opposite direction; when the actual temperature of the feed gas is equal to the reference temperature, the control unit maintains the output power of the ultrasonic transducer matrix unchanged; the ultrasonic transducer matrix emits a standing wave sound field to mechanically disturb and condense the warm and pressurized feed gas, separating decarbonized gas from the membrane separation decarbonization skid, as well as decarbonized gas carrying free water droplets formed due to the condensation process; S4. Dehydration: The decarbonized gas carrying free water droplets is passed into the pre-cyclone separator, and the free water droplets are removed by centrifugal sedimentation to obtain the initial dehydrated and decarbonized gas; after cooling the initial dehydrated and decarbonized gas to the second preset temperature range, it is passed into the molecular sieve skid for water adsorption treatment to obtain qualified dehydrated gas. S5. Cooling and separation: Cool the qualified dehydrated gas to the third preset temperature range to condense the C2+ component, and then pass it into a low-temperature separator for gas-liquid separation to obtain low-temperature gas phase and low-temperature liquid phase respectively. S6, Dry Gas Output: Dry gas is obtained by reheating the low-temperature gas phase to the fourth preset temperature range; the first part of the dry gas is fed into the CNG compressor for pressurization and then output; the second part of the dry gas is delivered to the gas generator set. S7, Hydrocarbon Removal and Stabilization: The low-temperature liquid phase is throttled and depressurized before being fed into the light hydrocarbon stabilization tower for distillation, separating the top gas phase and the bottom liquid phase of the light hydrocarbon stabilization tower; the bottom liquid phase of the light hydrocarbon stabilization tower is output as mixed hydrocarbons; the top gas phase of the light hydrocarbon stabilization tower is reheated to the fifth preset temperature range and then recycled back to the feed gas compressor inlet of S2 to mix with the primary filtered gas.

[0010] Furthermore, the first preset temperature range is 50℃ to 65℃; the second preset temperature range is less than or equal to 35℃; the third preset temperature range is -35℃ to -40℃; the fourth preset temperature range is 40℃; and the fifth preset temperature range is 40℃.

[0011] Furthermore, in S1, the raw gas passes through the inlet emergency shut-off valve and the pressure regulating valve in sequence before entering the inlet filter separator; the first stream of oily wastewater is discharged through the level regulating valve and transported to the wastewater storage tank.

[0012] Furthermore, the molecular sieve skid includes two parallel-arranged drying adsorption towers and a dust filter; the specific steps of the moisture adsorption treatment include: passing the initially dehydrated and decarbonized gas from the top of the tower into the drying adsorption tower in the adsorption state for moisture adsorption, and then passing it into the dust filter to remove solid impurities, thereby obtaining qualified dehydrated gas.

[0013] Furthermore, S4 also includes a molecular sieve adaptive regeneration cycle step based on variable load synergistic control: A gas flow meter and a moisture transmitter are installed on the inlet pipeline of the molecular sieve skid, and an early warning temperature sensor is installed in the two drying adsorption towers at a distance of 80% to 90% from the bed inlet height along the airflow direction. The control unit continuously collects real-time operating data and dynamically calculates the regeneration trigger threshold according to the following formula.

[0014]

[0015] in, This is the regeneration trigger threshold; t represents the adsorption time that the adsorption tower has been running continuously. Let α be the instantaneous volumetric flow rate of the dehydrated and decarbonized gas at time α. Let α be the initial moisture concentration of the dehydrated and decarbonized gas at time α. The total mass of molecular sieves packed in a single drying adsorption tower; This is the effective dynamic breakthrough water capacity constant of the molecular sieve; This is the temperature front sensitivity weighting coefficient, with a value ranging from 0.15 to 0.25; The real-time bed temperature measured by the temperature sensor is used for early warning. The inlet temperature of the gas after initial dehydration and decarbonization is the real-time temperature of the gas entering the tower. To determine the maximum theoretical temperature rise difference when the water adsorption zone passes through under calibrated operating conditions; When the control unit determines When the value is greater than or equal to the set critical value, the current adsorption operation of the drying adsorption tower is terminated prematurely, and the regeneration operation stage is triggered; when the determination is made... When the value is below the set critical value, maintain the current adsorption operation of the drying adsorption tower; The regeneration operation phase includes: Thermal regeneration stage: A portion of the dehydrated qualified gas is drawn from the outlet of the dust filter as regeneration gas; the regeneration gas is heated by the regeneration gas heater and then fed into the drying adsorption tower in the regeneration operation; when the temperature of the regeneration gas exiting the tower is greater than or equal to the first regeneration target temperature, the regeneration gas heater is stopped, and the thermal regeneration stage ends; when the temperature of the regeneration gas exiting the tower is less than the first regeneration target temperature, the thermal regeneration state is maintained. Cold blowing stage: Continue to introduce unheated regeneration gas into the drying adsorption tower; when the temperature of the regeneration gas exiting the tower is less than or equal to the second regeneration target temperature, the cold blowing stage ends; when the temperature of the regeneration gas exiting the tower is greater than the second regeneration target temperature, the cold blowing state is maintained. Regeneration gas recovery stage: The regeneration gas exiting the tower is cooled by a regeneration gas cooler, and then passed into a regeneration gas separator to separate the second stream of oily wastewater and regeneration reuse gas; the regeneration reuse gas is pressurized by a regeneration gas circulation fan and then circulated back to the inlet of the dry adsorption tower in adsorption operation, where it is mixed with the initial dehydration and decarbonization gas.

[0016] Furthermore, the critical value is set to 0.95; in the thermal regeneration stage, the target heating temperature of the regeneration gas heater is 230℃; the first regeneration target temperature is 210℃; and the second regeneration target temperature is 50℃.

[0017] Furthermore, in S5, the specific operation of the cooling separation step is as follows: the dehydrated qualified gas is introduced into a plate-fin heat exchanger and cooled to the sixth preset temperature range; the cooled dehydrated qualified gas is introduced into a refrigeration unit for further cooling to the third preset temperature range to obtain a gas-liquid mixture; the gas-liquid mixture is introduced into a low-temperature separator for gas-liquid separation to obtain a low-temperature gas phase and a low-temperature liquid phase; wherein, the sixth preset temperature range is 5.5℃.

[0018] Further, in S7, the dehydrocarbon stabilization step specifically includes: throttling and depressurizing the cryogenic liquid phase exiting the cryogenic separator to a first preset pressure value; passing the throttled and depressurized cryogenic liquid phase into a light hydrocarbon stabilization tower for distillation, controlling the top pressure of the light hydrocarbon stabilization tower to a second preset pressure value and the bottom temperature to a seventh preset temperature range, respectively obtaining the top gas phase and the bottom liquid phase of the light hydrocarbon stabilization tower; passing the top gas phase of the light hydrocarbon stabilization tower into a plate-fin heat exchanger for reheating to a fifth preset temperature range, and then circulating it back to the inlet of the feed gas compressor; wherein, the first preset pressure value and the second preset pressure value are both 1.3 MPaG, and the seventh preset temperature range is 45℃.

[0019] Furthermore, it also includes the steps of mixed hydrocarbon storage and transportation: The liquid phase at the bottom of the light hydrocarbon stabilization tower is passed into a mixed hydrocarbon storage tank for storage; the pressure inside the mixed hydrocarbon storage tank is controlled by a pressure regulating valve installed on the gas phase outlet pipeline of the mixed hydrocarbon storage tank. When pressurizing and transporting the liquid phase from the mixed hydrocarbon storage tank using a loading pump, control the process as follows: Loading preparation steps: After the loading arm is connected to the external tank car, open the priming and venting valve group of the loading pump to vent the air. Loading operation: Start the loading pump and open the outlet valve of the loading pump to start the loading operation; Loading completion action: When the loading operation is completed, simultaneously close the inlet valve and outlet valve of the loading pump.

[0020] Furthermore, it also includes standardizing wastewater treatment procedures: The first stream of oily wastewater, the compressor separation wastewater generated by the raw gas compressor, and the second stream of oily wastewater separated by the regenerated gas separator are all fed into the wastewater storage tank. Closed-loop interlock control is achieved between the temperature transmitter and the electric heater installed inside the wastewater storage tank. When the temperature inside the sewage storage tank is lower than the preset sewage maintenance temperature, the electric heater is turned on. When the temperature inside the sewage storage tank is greater than or equal to the preset sewage maintenance temperature, the electric heater is turned off. The process of pressurizing and transporting wastewater is controlled according to the following steps: Before starting the sewage pump, close the outlet valve of the sewage pump. After starting the sewage pump, control the opening of the outlet valve to pressurize and discharge the sewage in the sewage storage tank; During the operation of the sewage pump, gas is supplied to the sewage storage tank in one direction through the breather valve located on the top of the sewage storage tank to maintain the internal pressure state of the sewage storage tank.

[0021] The present invention has the following beneficial effects: 1. This invention recirculates all the gas phase separated from the top of the light hydrocarbon stabilization tower and the regenerated gas from the molecular sieve dehydration and regeneration cycle back to the feed gas compressor inlet for repressurization and recovery via a closed-loop pipeline. This design completely eliminates the resource waste and environmental pollution caused by the direct venting of hydrocarbon-rich tail gas in traditional open-loop processes, maximizing the extraction rate of hydrocarbon components.

[0022] 2. This invention targets low-pressure, wide-load wellhead gas (0.1~0.25 MPaG) by employing a dual purification barrier of membrane decarbonization and deep molecular sieve dehydration, strictly controlling CO2 content to ≤3 mol% and water content to ≤50 ppm. This not only ensures that carbonic acid corrosion does not occur when the dry gas is pressurized to 22.0 MPaG to produce CNG, but also effectively avoids the fatal failure of natural gas hydrate "ice blockage" in pipelines and valves during the -35℃ cryogenic dehydrocarbonization process.

[0023] 3. This invention uses temperature and pressure gradient control to precisely cut the complex wellhead gas into two types of high value-added products: CNG dry gas for export that meets stringent standards (also for self-use and power generation) and high-quality mixed hydrocarbons (NGL) that meet saturated vapor pressure requirements, which greatly improves the economic benefits of a single well gas field. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a low-pressure wellhead gas film separation and cryogenic combined decarbonization and dehydrocarbon recovery method according to an embodiment of the present invention. Detailed Implementation

[0025] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0026] Example As attached Figure 1 As shown in the figure, this embodiment provides a method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and dehydrocarbonization recovery, and the specific steps are as follows: S1, Filtration and Separation: The feed gas, with an inlet pressure of 0.1~0.25 MPaG and an inlet temperature ranging from 5~45℃, is fed into the inlet filter separator for metering and filtration. Before entering the inlet filter separator, the feed gas passes sequentially through an inlet emergency shut-off valve and a pressure regulating valve to ensure intake safety and pressure stability. This step separates and removes solid particles and tiny liquid droplets entrained in the feed gas, yielding primary filtered gas and the first stream of oily wastewater. The first stream of oily wastewater is discharged through a level regulating valve and directly transported to a unified wastewater storage tank at the downstream end.

[0027] S2, boost compression: The primary filtered gas is passed into a feed gas compressor (such as a screw compressor) with variable frequency control and pressurized to approximately 3.0 MPaG. In this step, the aftercooling parameters of the feed gas compressor are adjusted in real time by the control unit (e.g., adjusting the cooling fan speed or cooling water flow rate) to actively retain some of the compression heat and strictly control the exhaust temperature within a first preset temperature range (preferably 60°C in this embodiment, with a protection range of 50°C to 65°C), ultimately obtaining warm, pressurized feed gas carrying the heat of compression.

[0028] S3, Membrane decarbonization step: The heated and pressurized feed gas is introduced into a membrane separation decarbonization skid equipped with an ultrasonic transducer matrix. Utilizing the heat carried by the pressurized feed gas itself, the viscous resistance of the gas within the membrane module can be effectively reduced, and the permeability of the polymer membrane can be improved. During the decarbonization process, the control unit implements a temperature-power closed-loop reverse regulation control: the actual temperature entering the membrane is collected in real time and compared with a set reference temperature; when the actual temperature entering the membrane deviates from the reference temperature, the control unit controls the output power of the ultrasonic transducer matrix to adjust in the opposite direction (i.e., when the temperature entering the membrane decreases, the ultrasonic power is increased to compensate for energy disturbance; when the temperature entering the membrane is too high, the ultrasonic power is decreased to save energy); when the actual temperature entering the membrane equals the reference temperature, the ultrasonic output power remains constant. The ultrasonic transducer matrix emits a standing wave sound field within the membrane tube, which not only mechanically disturbs the airflow and strips the concentration polarization layer on the membrane surface, but also utilizes the ultrasonic condensation effect to promote the collision of micron-sized aerosols, ultimately separating decarbonized gas (CO2 content ≤ 3Mol%), and free large water droplets carried in the decarbonized gas due to condensation.

[0029] S4, Dehydration and Molecular Sieve Regeneration Cycle: This step is divided into two stages: pre-physical deloading and deep adsorption by molecular sieves. Pre-load unloading: The decarbonized gas carrying the free water droplets is first passed into the pre-cyclone separator. The large-diameter free water droplets formed by ultrasonic condensation are completely separated and removed by centrifugal sedimentation, which greatly reduces the water load of the subsequent molecular sieve and obtains the initial dewatered and decarbonized gas. Deep dehydration and adaptive regeneration: After cooling the initially dehydrated and decarbonized gas to a second preset temperature range (preferably 30℃ in this embodiment, ≤35℃ required), it is passed into a molecular sieve skid for moisture adsorption treatment. The molecular sieve skid includes two parallel-arranged drying adsorption towers and a dust filter. The initially dehydrated and decarbonized gas is passed from the top of the tower into the drying adsorption tower in the adsorption state, and then passed into the dust filter to remove solid impurities, obtaining a qualified dehydrated gas with extremely low water content (≤50ppm).

[0030] During adsorption operations, the control unit executes an adaptive regeneration cycle of the molecular sieve based on variable load coordinated control: through gas flow meters and moisture transmitters installed on the inlet pipeline, and early warning temperature sensors installed in the adsorption tower at 80%~90% of the bed inlet height along the airflow direction, the control unit continuously collects real-time operating data and dynamically calculates the regeneration trigger threshold according to the following formula. :

[0031] in, The regeneration trigger threshold is t; t is the adsorption time during which the adsorption tower has been running continuously. Let α be the instantaneous volumetric flow rate of the dehydrated and decarbonized gas at time α. Let α be the initial moisture concentration of the dehydrated and decarbonized gas at time α. The total mass of molecular sieves packed in a single drying adsorption tower; This is the effective dynamic breakthrough water capacity constant of the molecular sieve; This is the temperature front sensitivity weighting coefficient, with a value ranging from 0.15 to 0.25; The real-time bed temperature measured by the temperature sensor is used for early warning. The inlet temperature of the gas after initial dehydration and decarbonization is the real-time temperature of the gas entering the tower. To determine the maximum theoretical temperature rise difference when the water adsorption zone passes through under calibrated operating conditions; When the control unit determines When the value is greater than or equal to the set critical value (preferably 0.95), it indicates that the bed is about to be penetrated, and the system will end the current adsorption operation of the drying adsorption tower in advance and automatically trigger the regeneration operation stage.

[0032] The regeneration operation phase includes: (1) Thermal regeneration stage: A portion of the dehydrated qualified gas is drawn out as regeneration gas, heated to the target heating temperature (230℃) by the regeneration gas heater and then introduced into the drying adsorption tower; when the temperature of the regeneration gas exiting the tower is ≥210℃ (the first regeneration target temperature), the heater is stopped and the thermal regeneration ends. (2) Cold blowing stage: Continue to introduce unheated regeneration gas. When the temperature of the regeneration gas exiting the tower is ≤ 50℃ (second regeneration target temperature), the cold blowing ends. (3) Regeneration gas recovery stage: The regeneration gas exiting the tower is cooled and then passed into the regeneration gas separator to separate the second stream of oily wastewater, and then the regeneration gas is reused. This gas is pressurized by the circulating fan and returned to the inlet of the adsorption tower to mix with the main gas flow, so as to achieve "zero emission" of regeneration waste gas.

[0033] S5, Cooling Separation: The dehydrated qualified gas is first passed through a plate-fin heat exchanger and cooled to the sixth preset temperature range (5.5℃); then it is passed through a refrigeration unit for further deep cooling to the third preset temperature range (preferably -35℃ in this embodiment, with a protection range of -35℃ to -40℃). At this temperature, the C2+ (ethane and higher heavy components) carried in the gas undergoes supersaturated condensation to obtain a gas-liquid mixture; this mixture is then passed through a cryogenic separator for gas-liquid separation, extracting the cryogenic gas phase and cryogenic liquid phase respectively.

[0034] S6, Dry Gas Output: The low-temperature gas phase at the top of the low-temperature separator is reintroduced into the plate-fin heat exchanger to exchange heat with the incoming gas, reheating itself to the fourth preset temperature range (40°C) to obtain dry gas. The dry gas is then split: the first part is fed into a CNG compressor and pressurized to approximately 22.0 MPaG before being output through a refueling column; the second part is delivered to a gas generator set to provide power support for on-site equipment.

[0035] S7, Dehydrocarbonization Stabilization Step: The cryogenic liquid phase is throttled and depressurized to a first preset pressure value (1.3 MPaG), and then fed into a light hydrocarbon stabilization column for distillation. The top pressure of the column is strictly controlled at a second preset pressure value (1.3 MPaG), and the bottom temperature is within the seventh preset temperature range (45°C). The light hydrocarbon stabilization column bottom liquid phase, whose saturated vapor pressure meets the standard, is output as high-quality mixed hydrocarbons (NGL). The light hydrocarbon stabilization column top gas phase, after being reheated to the fifth preset temperature range (40°C), is circulated back to the feed gas compressor inlet of S2 via the reflux pipeline. This closed-loop design completely eliminates the venting pollution of hydrocarbon-rich tail gas and improves the recovery rate of hydrocarbon resources.

[0036] Mixed hydrocarbon storage and transportation steps: The liquid phase (mixed hydrocarbons) from the bottom of the light hydrocarbon stabilization tower output from S7 is passed into a mixed hydrocarbon storage tank for storage. A pressure regulating valve is installed on the gas phase outlet pipeline of the mixed hydrocarbon storage tank, and the pressure inside the storage tank is controlled by the valve opening.

[0037] When transporting goods to the outside, first connect the external tanker to the loading arm; open the priming and venting valve group of the loading pump to prime and vent the pump; after venting is completed, start the loading pump and open the pump outlet valve to carry out the loading operation, and observe the pump operation status during the process; when the loading operation is completed, simultaneously close the inlet valve and outlet valve of the loading pump to ensure safe disconnection.

[0038] Standardized wastewater treatment procedures: This process incorporates a centralized wastewater treatment skid. The first stream of oily wastewater generated by the S1 inlet filter separator, the compressor separation wastewater generated by the S2 feed gas compressor, and the second stream of oily wastewater separated by the S4 regeneration gas separator are all collected through a pipeline network and fed into a wastewater storage tank.

[0039] To prevent sewage from freezing in extremely cold conditions, an electric heater is installed inside the sewage storage tank. A temperature transmitter is used in a closed-loop interlock with the electric heater to automatically maintain the set temperature inside the tank. Additionally, a breather valve with a flame arrester is installed on the top of the sewage storage tank.

[0040] When discharging sewage, the following anti-cavitation operating procedures should be followed: Before starting the sewage pump, close the outlet valve; after starting the sewage pump, slowly open the outlet valve to pressurize the sewage in the storage tank and send it to the sewage tanker truck. During the high-speed pumping operation of the sewage pump, the breather valve with a flame arrester automatically replenishes air into the sewage storage tank, effectively avoiding and limiting tank collapse accidents caused by excessive vacuum in the sewage storage tank. After loading is completed, close the sewage pump outlet valve.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery, characterized in that, Includes the following steps: S1. Filtration and separation: The raw gas is passed into the inlet filter separator to separate and remove solid particles and tiny droplets from the raw gas, resulting in primary filtered gas and the first stream of oily wastewater. S2, Pressurization and Compression: The primary filtered gas is introduced into a raw material gas compressor with frequency conversion control for pressurization; the exhaust temperature is controlled within the first preset temperature range by adjusting the aftercooling parameters of the raw material gas compressor through the control unit to obtain warm and pressurized raw material gas; S3. Membrane Decarbonization: The heated and pressurized feed gas is introduced into a membrane separation decarbonization skid equipped with an ultrasonic transducer matrix; the control unit collects the actual temperature of the feed gas in real time and compares it with the set reference temperature: when the actual temperature of the feed gas deviates from the reference temperature, the control unit controls the output power of the ultrasonic transducer matrix to increase or decrease in the opposite direction; when the actual temperature of the feed gas is equal to the reference temperature, the control unit maintains the output power of the ultrasonic transducer matrix unchanged; the ultrasonic transducer matrix emits a standing wave sound field to mechanically disturb and aerosol condensate the heated and pressurized feed gas, and decarbonized gas carrying free water droplets is separated from the membrane separation decarbonization skid; S4. Dehydration: The decarbonized gas carrying free water droplets is passed into a pre-cyclone separator, and the free water droplets are removed by centrifugal sedimentation to obtain initial dehydrated and decarbonized gas; after cooling the initial dehydrated and decarbonized gas to a second preset temperature range, it is passed into a molecular sieve skid for water adsorption treatment to obtain qualified dehydrated gas. S5. Cooling and separation: Cool the dehydrated qualified gas to a third preset temperature range to condense the C2+ component, and then pass it into a low-temperature separator for gas-liquid separation to obtain a low-temperature gas phase and a low-temperature liquid phase respectively. S6. Dry gas output: Dry gas is obtained by reheating the low-temperature gas phase to the fourth preset temperature range. The first portion of the dry gas is fed into a CNG compressor for pressurization and then output; the second portion of the dry gas is delivered to a gas generator set. S7. Hydrocarbon removal and stabilization: The low-temperature liquid phase is throttled and depressurized before being fed into a light hydrocarbon stabilization tower for distillation, separating the top gas phase and the bottom liquid phase of the light hydrocarbon stabilization tower; the bottom liquid phase of the light hydrocarbon stabilization tower is output as a mixed hydrocarbon. After the gas phase at the top of the light hydrocarbon stabilization tower is reheated to the fifth preset temperature range, it is recycled back to the feed gas compressor inlet of S2 and mixed with the primary filtered gas.

2. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 1, characterized in that, The first preset temperature range is 50℃ to 65℃; the second preset temperature range is less than or equal to 35℃; the third preset temperature range is -35℃ to -40℃; the fourth preset temperature range is 40℃; and the fifth preset temperature range is 40℃.

3. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 1, characterized in that, In step S1, the raw gas passes through the inlet emergency shut-off valve and the pressure regulating valve in sequence before entering the inlet filter separator; the first stream of oily wastewater is discharged through the liquid level regulating valve and transported to the wastewater storage tank.

4. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 1, characterized in that, The molecular sieve skid includes two drying adsorption towers arranged in parallel and a dust filter; The specific steps of the moisture adsorption treatment include: passing the initial dehydrated and decarbonized gas from the top of the tower into the drying adsorption tower in the adsorption state for moisture adsorption, and then passing it into the dust filter to remove solid impurities, thereby obtaining the qualified dehydrated gas.

5. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 4, characterized in that, S4 further includes a molecular sieve adaptive regeneration cycle step based on variable load coordinated control: A gas flow meter and a moisture transmitter are installed on the inlet pipeline of the molecular sieve skid, and an early warning temperature sensor is installed in the two drying adsorption towers at a distance of 80% to 90% from the bed inlet height along the airflow direction. The control unit continuously collects real-time operating data and dynamically calculates the regeneration trigger threshold according to the following formula. in, This is the regeneration trigger threshold; t represents the adsorption time that the adsorption tower has been running continuously. The instantaneous volumetric flow rate of the initial dehydration and decarbonization gas at time α; The water mass concentration of the initial dehydrated and decarbonized gas at time α; The total mass of molecular sieves packed in a single drying adsorption tower; This is the effective dynamic breakthrough water capacity constant of the molecular sieve; This is the temperature front sensitivity weighting coefficient, with a value ranging from 0.15 to 0.25; The real-time temperature of the bed measured by the warning temperature sensor; The inlet temperature of the initial dehydration and decarbonization gas is the real-time temperature of the gas entering the tower. To determine the maximum theoretical temperature rise difference when the water adsorption zone passes through under calibrated operating conditions; When the control unit determines When the value is greater than or equal to a set critical value, the current adsorption operation of the drying adsorption tower is terminated prematurely, and the regeneration operation phase is triggered; when it is determined that... When the value is less than the set critical value, the current adsorption operation of the drying adsorption tower is maintained; The regeneration operation phase includes: Thermal regeneration stage: A portion of the dehydrated qualified gas is drawn from the outlet of the dust filter as regeneration gas; the regeneration gas is heated by the regeneration gas heater and then fed into the drying adsorption tower in the regeneration operation; when the temperature of the regeneration gas exiting the tower is greater than or equal to the first regeneration target temperature, the regeneration gas heater is stopped, and the thermal regeneration stage ends; when the temperature of the regeneration gas exiting the tower is less than the first regeneration target temperature, the thermal regeneration state is maintained. Cold blowing stage: Continue to introduce unheated regenerated gas into the drying adsorption tower; when the temperature of the regenerated gas exiting the tower is less than or equal to the second regeneration target temperature, the cold blowing stage ends; when the temperature of the regenerated gas exiting the tower is greater than the second regeneration target temperature, the cold blowing state is maintained. Regeneration gas recovery stage: The regeneration gas exiting the tower is passed into a regeneration gas cooler for cooling, and then passed into a regeneration gas separator to separate the second stream of oily wastewater and regeneration reuse gas; the regeneration reuse gas is pressurized by a regeneration gas circulation fan and then circulated back to the inlet of the dry adsorption tower in the adsorption operation, where it is mixed with the initial dehydration and decarbonization gas.

6. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 5, characterized in that, The set critical value is 0.95; in the thermal regeneration stage, the target heating temperature of the regeneration gas heater is 230°C; the first regeneration target temperature is 210°C; and the second regeneration target temperature is 50°C.

7. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 1, characterized in that, In step S5, the specific operation of the cooling separation step is as follows: the dehydrated qualified gas is introduced into a plate-fin heat exchanger and cooled to a sixth preset temperature range; the cooled dehydrated qualified gas is introduced into a refrigeration unit and further cooled to a third preset temperature range to obtain a gas-liquid mixture; the gas-liquid mixture is introduced into a low-temperature separator for gas-liquid separation to obtain a low-temperature gas phase and a low-temperature liquid phase; wherein, the sixth preset temperature range is 5.5℃.

8. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 5, characterized in that, In step S7, the dehydrocarbon stabilization step specifically includes: throttling and depressurizing the cryogenic liquid phase exiting the cryogenic separator to a first preset pressure value; passing the throttled and depressurized cryogenic liquid phase into the light hydrocarbon stabilization tower for distillation, controlling the top pressure of the light hydrocarbon stabilization tower to a second preset pressure value and the bottom temperature to a seventh preset temperature range, thereby obtaining the top gas phase and the bottom liquid phase of the light hydrocarbon stabilization tower respectively; passing the top gas phase of the light hydrocarbon stabilization tower into a plate-fin heat exchanger for reheating to the fifth preset temperature range, and then circulating it back to the inlet of the feed gas compressor; wherein, the first preset pressure value and the second preset pressure value are both 1.3 MPaG, and the seventh preset temperature range is 45°C.

9. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 8, characterized in that, It also includes the storage and transportation steps for mixed hydrocarbons: The bottom liquid phase of the light hydrocarbon stabilizing tower is passed into a mixed hydrocarbon storage tank for storage; the pressure inside the mixed hydrocarbon storage tank is controlled by a pressure regulating valve installed on the gas phase outlet pipeline of the mixed hydrocarbon storage tank. When the liquid phase in the mixed hydrocarbon storage tank is pressurized and transported out via a loading pump, the following steps shall be followed for control: Loading preparation steps: After the loading arm is connected to the external tank truck, open the priming and exhaust valve group of the loading pump to exhaust air. Loading operation: Start the loading pump and open the outlet valve of the loading pump to carry out the loading operation; Loading completion action: When the loading operation is completed, the inlet valve of the loading pump and the outlet valve of the loading pump are closed simultaneously.

10. The method for low-pressure wellhead gas film separation and cryogenic combined decarbonization and hydrocarbon recovery according to claim 5, characterized in that, It also includes standardized wastewater treatment procedures: The first stream of oily wastewater, the compressor separation wastewater generated by the raw gas compressor, and the second stream of oily wastewater separated by the regeneration gas separator are all fed into the wastewater storage tank. Closed-loop interlock control is achieved between the temperature transmitter and the electric heater installed inside the wastewater storage tank. When the temperature inside the wastewater storage tank is lower than the preset wastewater maintenance temperature, the electric heater is turned on. When the temperature inside the wastewater storage tank is greater than or equal to the preset wastewater maintenance temperature, the electric heater is turned off. The process of pressurizing and transporting wastewater is controlled according to the following steps: Before starting the sewage pump, control the closing of the sewage pump's outlet valve; After the sewage pump is started, the outlet valve is opened to pressurize and discharge the sewage in the sewage storage tank. During the operation of the sewage pump, gas is supplied unidirectionally into the sewage storage tank through a breather valve located on the top of the sewage storage tank to maintain the internal pressure state of the sewage storage tank.

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