An adaptive variable-condition oil recovery system for near-zero emissions and its operating method

Abstract

This invention discloses an adaptive variable-condition oil recovery system for near-zero emissions and its operating method. Under low operating pressure conditions, this invention effectively addresses severe fluctuations caused by the lack of stable pressure at the front end through a three-stage stabilization architecture. Under adaptive control, the Pressure Swing Adsorption (PSA) unit maintains stable separation performance even when using only vacuum desorption regeneration, under high-fluctuation loads. This invention eliminates the need for a high-power feed gas compressor, significantly reducing equipment investment; low-pressure operation reduces equipment wall thickness and material requirements, further saving costs; the PSA regeneration process eliminates the complex purge gas system, simplifying the system structure, reducing initial investment and maintenance costs, and avoiding purge gas consumption or product gas loss.

Description

Technical Field

[0001] This invention relates to the field of associated gas treatment and carbon capture, utilization and storage (CCUS) technology in oilfields, and particularly to an adaptive variable-condition oil recovery system for near-zero emissions of produced gas and its operating method. Background Technology

[0002] In enhanced oil recovery (EOR) processes using carbon dioxide flooding, the associated gas produced alongside the crude oil (hereinafter referred to as "produced gas") typically undergoes preliminary gas-liquid-water separation in a three-phase separator. Due to safety regulations and process constraints, large gas holders or constant-pressure storage tanks are often not permitted downstream of the three-phase separator. This results in drastic and irregular fluctuations in both the flow rate and CO2 concentration of the produced gas upon entering the gas processing system (flow rate fluctuations can reach ±50% or more, and CO2 concentrations can change rapidly within a wide range of 30%-90%). This strong volatility poses the following serious challenges to subsequent gas separation and purification processes, with traditional processes exhibiting poor adaptability: For pressure swing adsorption (PSA) processes, under highly volatile inlet gas conditions, fixed-cycle operation can easily lead to adsorbent breakthrough during peak flow periods, resulting in substandard product gas; during low flow periods, insufficient adsorbent regeneration affects the performance of the next cycle. More importantly, traditional PSA processes require high operating pressures, often needing to boost the feed gas to 0.8 MPa or even higher to ensure the separation performance and adsorption capacity of the adsorbent. This means that a high-power feed gas compressor must be configured at the front end, increasing system energy consumption, investment, and maintenance costs. Some PSA processes use product gas purging regeneration, which helps improve regeneration efficiency, but results in the loss of valuable product gas and an increase in cycle energy consumption. The performance of membrane separation units is particularly sensitive to inlet gas pressure and composition; fluctuations and certain components can significantly affect their separation efficiency and membrane life. High equipment operation risk: Severe flow fluctuations can easily lead to unstable operation of power equipment such as compressors, shortening equipment life and increasing subsequent maintenance costs. Low resource recovery rate and emissions: To maintain system stability, or due to incomplete regeneration leading to a decrease in separation efficiency, traditional processes may result in insufficient recovery of hydrocarbon resources or direct emissions of greenhouse gas CO2. High system energy consumption: Under fluctuating operating conditions, the system is difficult to operate at its design optimal point. If the PSA regeneration process is complex (such as involving heating or high-pressure purging), or if the cold energy of the flash vapor (BOG) generated during liquefaction is not recovered, energy waste will occur.

[0003] Currently, although various associated gas treatment and carbon capture solutions exist, none have effectively solved the challenges of efficient separation and complete regeneration of highly fluctuating, high-concentration CO2 produced gas under low operating pressure conditions. How to simplify the process, avoid product gas loss, and reduce energy consumption while ensuring efficient adsorbent regeneration remains an unresolved issue. There is a lack of comprehensive, integrated solutions encompassing front-end fluctuation suppression, adaptive process control, simplified and efficient regeneration, and end-of-pipe energy recovery. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose an adaptive variable-condition oil recovery gas near-zero emission recovery system and its working method.

[0006] In a first aspect, the present invention proposes an adaptive variable-condition oil recovery gas near-zero emission recovery system, comprising:

[0007] The associated gas from the oilfield is initially purified in the purification unit to obtain purified gas. The pressure swing adsorption unit is located downstream of the purification unit. The pressure swing adsorption unit includes a buffer tank 1, a pressure swing adsorption device and a water ring vacuum pump arranged sequentially upstream and downstream. The purified gas is adsorbed and separated by the adsorbent in the pressure swing adsorption device to obtain natural gas. The adsorbent is desorbed by the water ring vacuum pump to obtain CO2 enriched gas and stored in the buffer tank 3. The membrane separation and purification unit, located downstream of the pressure swing adsorption unit, allows the CO2-enriched gas in buffer tank three to pass through a first filtration, pressurization, gas-water separation, and a second filtration before entering the membrane unit to obtain high-purity CO2, which is then stored in buffer tank four. The liquefaction unit, located downstream of the membrane separation and purification unit, receives high-purity CO2 from buffer tank four. After being pressurized, separated from water, filtered, and dried, the CO2 enters the all-liquid evaporator to obtain high-purity liquid CO2, which is then stored in a temporary storage tank. A refrigeration unit, which provides cooling capacity for the water ring vacuum pump and the all-liquid evaporator.

[0008] Furthermore, a regulating valve and a pressure sensor are installed on the natural gas outlet pipeline of the pressure swing adsorption device. The opening of the regulating valve is adjusted in real time according to the pressure sensor to stabilize the adsorption pressure in the pressure swing adsorption device.

[0009] Furthermore, a flow detector is installed at the air inlet of the pressure swing adsorption device. The flow rate of the purified gas is divided into multiple flow ranges according to the flow detector, and the time of each step in the pressure swing adsorption cycle is dynamically adjusted according to the flow range.

[0010] Furthermore, the adsorbent includes one of molecular sieves and MOF materials, and the adsorbent selectively separates CO2 and CH4 at 0.25~0.55 MPa.

[0011] Furthermore, the purification unit includes a multi-stage pipeline filter, a desulfurization tower, and a refrigerated dryer arranged sequentially upstream and downstream. The associated gas from the oilfield is purified after passing through the multi-stage pipeline filter to remove solid particles and water mist, the desulfurization tower to remove sulfur, and the refrigerated dryer to remove water vapor. The purified gas is then stored in the buffer tank.

[0012] Furthermore, after the natural gas flows out through the pressure swing adsorption device, it enters the second buffer tank. The natural gas in the second buffer tank is pressurized by a booster and then transported to the natural gas recovery station.

[0013] Furthermore, the membrane separation and purification unit utilizes a coalescing filter, a first pressurization assembly, a steam-water separator, and a filter to perform the first filtration, pressurization, steam-water separation, and second filtration processes, respectively. The first pressurization assembly includes an oil-injected screw compressor, an oil separator, and a heat exchanger arranged sequentially upstream and downstream.

[0014] Furthermore, the liquefaction unit utilizes the second pressurization component, the second steam-water separator, the second filter, and the desiccant dryer to perform the pressurization, steam-water separation, filtration, and drying processes, respectively. The second pressurization component includes the second oil-injected screw compressor, the second oil separator, and the second heat exchanger arranged sequentially upstream and downstream. When the desiccant dryer operates in a dual-tower alternating mode, the purge gas generated enters the third buffer tank. The non-condensable gas in the temporary storage tank enters the third buffer tank after the heat exchanger recovers its cooling capacity.

[0015] Furthermore, the high-purity liquid CO2 in the temporary storage tank enters the large liquid CO2 storage tank, and the non-condensable gas in the large liquid CO2 storage tank enters the buffer tank.

[0016] Secondly, this invention proposes a working method for a desulfurization wastewater extraction process system, which utilizes the system proposed in the first aspect and includes the following steps: Associated gas from the oilfield is initially purified by the purification unit to obtain purified gas, which then enters buffer tank one. Under the stabilizing effect of buffer tank 1 and regulating valve, the pressure swing adsorption unit produces natural gas at low pressure according to a specific cycle. The adsorbent is desorbed by a water ring vacuum pump to obtain CO2 enriched gas. The CO2-enriched gas enters the membrane separation and purification unit, where it is compressed, purified, and separated by a membrane to obtain high-purity CO2. Meanwhile, the methane-rich tail gas generated is returned to buffer tank 1. High-purity CO2 enters the liquefaction unit and is compressed, purified, and cryogenically liquefied to obtain high-purity liquid CO2, which is temporarily stored in a temporary storage tank. The non-condensable gas in the temporary storage tank enters the buffer tank after the recovered cold energy. High-purity CO2 or vaporized liquid CO2 is reinjected into the formation for oil displacement.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention effectively addresses severe fluctuations under low operating pressure conditions through a three-stage stabilization architecture. Under adaptive control, the PSA unit can maintain stable separation performance even when using only vacuum desorption regeneration, even under high fluctuating loads.

[0018] This invention eliminates the need for a high-power feed gas compressor, significantly reducing equipment investment; low-pressure operation reduces equipment wall thickness and material requirements, further saving costs; the PSA regeneration process eliminates the complex purge gas system, simplifying system composition, reducing initial investment and maintenance costs, while avoiding purge gas consumption or product gas loss.

[0019] The system of this invention achieves fully enclosed operation with zero venting of process gases and generates only a small amount of treatable wastewater, resulting in significant environmental benefits. The skid-mounted and simplified process design makes the system more reliable, easy to transport, and quick to deploy. More than 2,000 hours of continuous and stable operation in pilot testing has proven the high reliability and engineering practicality of the system.

[0020] This invention has extremely high product quality and recovery rate. Specifically, the CH4 purity in the purified natural gas is ≥92%, and the CO2 content is ≤4%, meeting pipeline transportation standards. The CO2 purity of the product is ≥95%, meeting the requirements for reinjection and industrial utilization. The total hydrocarbon recovery rate is ≥99%, and the CO2 recovery rate is ≥99.5%. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein: Figure 1 This is a schematic diagram of the adaptive variable operating condition oil recovery gas near-zero emission recovery system of the present invention; Figure 2 This is a schematic diagram illustrating the arrangement of the flow detector, pressure sensor, and regulating valve of the present invention. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following description, in conjunction with the accompanying drawings, describes the adaptive variable-condition oil recovery gas near-zero emission recovery system and its operating method proposed in this invention. Figure 1 and Figure 2 As shown, the adaptive variable operating condition oil recovery gas near-zero emission recovery system of the present invention includes a purification unit, a pressure swing adsorption unit, a membrane separation and purification unit, a liquefaction unit and a refrigeration unit arranged sequentially upstream and downstream.

[0024] The purification unit comprises a multi-stage pipeline filter, a desulfurization tower, and a refrigerated dryer arranged sequentially upstream and downstream. The multi-stage pipeline filters, arranged in series, remove particulate matter and water mist from associated gas from the oilfield, which is a mixture separated by a three-phase separator. The desulfurization tower employs dry or wet desulfurization processes to remove sulfides such as H2S. The refrigerated dryer is used for deep removal of water vapor from the gas. Liquid water, hydrocarbons, and desulfurization wastewater generated by the multi-stage pipeline filters and desulfurization tower are collected and treated in a waste liquid tank.

[0025] The pressure swing adsorption (PSA) unit includes a buffer tank, a pressure swing adsorption device, and a water ring vacuum pump arranged sequentially upstream and downstream. The buffer tank is located at the front end of the pressure swing adsorption device. The associated gas from the oilfield is initially purified by the purification unit to obtain purified gas, which enters the buffer tank. The buffer tank is used to perform final pressure and flow buffering of the purified gas.

[0026] The pressure swing adsorption (PSA) unit employs a multi-tower (e.g., 6-tower, 8-tower, 12-tower) vacuum pressure swing adsorption (VPSA) process. The PSA unit contains an adsorbent, which includes one of the following: molecular sieves or MOFs (metal-organic frameworks). The adsorbent can selectively separate CO2 and CH4 at 0.25–0.55 MPa. The adsorbent used in this invention is a high-performance, specialized adsorbent that maintains excellent CO2 adsorption capacity and extremely high CO2 / CH4 separation selectivity even at low CO2 partial pressures (corresponding to a total feed gas pressure of 0.25–0.55 MPa). This allows the PSA unit to achieve separation performance comparable to high-pressure PSA at lower pressures. Compared to existing adsorbents, the adsorbent used in this invention maintains a high CO2 / CH4 separation ratio even at lower CO2 partial pressures.

[0027] Due to the characteristics of the adsorbent, the pressure swing adsorption (PSA) unit can directly utilize the outlet pressure of the three-phase separator without the need for a feed gas booster compressor. The gas enters the PSA unit directly after being buffered in buffer tank one. The purified gas undergoes selective separation of CO2 and CH4 by the adsorbent in the PSA unit. The PSA unit produces qualified low-concentration CO2 natural gas (CH4), which enters buffer tank two. The natural gas in buffer tank two has a CH4 purity ≥92% and a CO2 content ≤4%, meeting pipeline transportation standards. The natural gas in buffer tank two is then pressurized by a booster compressor and transported to a natural gas recovery station.

[0028] The adsorbent is desorbed by a water ring vacuum pump to obtain CO2-enriched gas, which is stored in buffer tank three. The water ring vacuum pump provides the core power for the regeneration of the adsorbent and is used to perform the vacuum desorption step to desorb the adsorbed CO2. This invention does not require an air compressor or product gas recirculation compressor for regeneration purging; regeneration relies solely on the water ring vacuum pump to complete the desorption. In this invention, the air compressor is located upstream of the pressure swing adsorption device. The air compressor's function is to provide high-quality compressed air, referred to as "instrument air" or "instrument wind," to the pneumatic valve assembly as a power source to drive the pneumatic actuator, thereby controlling the opening and closing of the valves.

[0029] In this invention, a regulating valve and a pressure sensor are installed on the natural gas outlet pipeline of the pressure swing adsorption (PSA) unit. Specifically, the regulating valve is located on the outlet pipeline of the PSA unit's decarbonized product gas (natural gas). The regulating valve and the pressure sensor on the natural gas outlet pipeline are interlocked in real time. The opening of the regulating valve is adjusted according to the pressure sensor to stabilize the adsorption pressure within the PSA unit. Specifically, when the natural gas outlet pressure changes abruptly due to fluctuations in the upstream purified gas pressure, the regulating valve quickly adjusts its opening to stabilize the adsorption pressure within the PSA unit, preventing drastic changes in the purified gas flow rate from causing disturbance or penetration of the adsorbent bed. It can be understood that when the pressure sensor detects an increase in the upstream purified gas pressure, the opening of the regulating valve increases accordingly; when the pressure sensor detects a decrease in the upstream purified gas pressure, the opening of the regulating valve decreases accordingly.

[0030] A flow detector is installed at the inlet of the pressure swing adsorption (PSA) unit to divide the purified gas flow rate into multiple flow ranges. The time of each step in the PSA cycle is dynamically adjusted according to these flow ranges, especially the adsorption time and vacuum desorption time, to match the inlet gas load and ensure regeneration efficiency. Examples of decarbonization adsorption and vacuum desorption times under different feed gas concentrations are shown in Tables 1 and 2 below.

[0031] Table 1:

[0032] Table 2:

[0033] The pressure swing adsorption unit of this invention is the core separation unit, which performs coarse separation of CO2 and CH4 at room temperature and adopts a simplified regeneration process of vacuum desorption only, achieving efficient operation under low pressure (0.25~0.55).

[0034] The pressure swing adsorption unit of the present invention uses an adsorbent that allows the pressure swing adsorption device to operate stably in a lower pressure range of 0.25-0.55 MPa. It directly utilizes the process pressure of the front-end three-phase separator, eliminating the need for a high-power feed gas compressor, thus reducing system energy consumption and consequently lowering costs.

[0035] The pressure swing adsorption (PSA) unit of this invention adopts a three-stage fluctuation suppression and adaptive control architecture. It utilizes a buffer tank to achieve the first-stage physical buffering, and uses the regulating valve and pressure sensor of the natural gas outlet pipeline of the PSA device to interlock and control in real time to counteract pressure disturbances and achieve the second-stage active pressure stabilization regulation. It dynamically adjusts the time of each step in the PSA cycle according to the flow range to achieve the third-stage process adaptation.

[0036] The regeneration of the pressure swing adsorption device of the present invention relies entirely on the vacuum environment provided by the water ring vacuum pump for desorption, eliminating the product gas purging or additional gas source purging steps commonly used in traditional processes, simplifying the process, reducing equipment investment and operational complexity, and avoiding product gas loss or additional energy consumption caused by purging.

[0037] The membrane separation and purification unit is used to purify the CO2-enriched gas desorbed from the pressure swing adsorption (PSA) unit. The unit includes a buffer tank (3), a coalescing filter, a first pressurization component, a gas-liquid separator (1), and a filter (1). The CO2-enriched gas in buffer tank (3) undergoes a first filtration via the coalescing filter, is pressurized by the first pressurization component, separates gas and water in the gas-liquid separator (1), and undergoes a second filtration in the filter (1) before entering the membrane module unit. In the membrane module unit, utilizing the difference in gas permeation rates, the CO2 is further purified to ≥95%, yielding high-purity CO2, which is stored in a buffer tank (4). Simultaneously, methane-rich permeate tail gas is generated and, as non-permeate gas, is returned to the upstream buffer tank (1), achieving a closed-loop cycle and near-total recovery of methane and other hydrocarbon components. Furthermore, the high-purity CO2 generated by the membrane module unit can be pressurized to the required high pressure for the reservoir using a reinjection compressor and reinjected into the formation for oil displacement. In some embodiments, the membrane module unit may use flat sheet membranes, hollow fiber membranes, etc.

[0038] The first pressurization assembly includes an oil-injected screw compressor, an oil separator, and a heat exchanger arranged sequentially upstream and downstream. This assembly pressurizes the CO2-enriched gas to the pressure required for membrane separation. Additionally, wastewater generated by the buffer tank, coalescing filter, gas-liquid separator, and filter is recycled into a waste liquid tank.

[0039] The liquefaction unit is located downstream of the membrane separation and purification unit. It liquefies and stores high-purity CO2. The high-purity CO2 in buffer tank four undergoes sequential pressurization, gas-liquid separation, filtration, and drying before entering the all-liquid evaporator to obtain high-purity liquid CO2, which is then stored in a temporary storage tank. The liquefaction unit uses buffer tank four to receive and stabilize the high-purity CO2 product gas from the membrane unit. The high-purity CO2 is then subjected to multi-stage compression using the second pressurization component. Gas-liquid separator two, filter two, and a desiccant dryer perform gas-liquid separation, filtration, and drying processes respectively, thereby deeply removing oil, water, and trace impurities from the compressed CO2. Wastewater generated by gas-liquid separator two and filter two is recycled into a waste liquid tank.

[0040] The second pressurization assembly includes an oil-injected screw compressor (II), an oil separator (II), and a heat exchanger (II) arranged sequentially upstream and downstream. Non-condensable gases from the temporary storage tank undergo cooling via heat exchanger (II) to pre-cool CO2 before entering buffer tank (III) for further recovery, thus saving 10%-20% of energy consumption and reducing CO2 emissions. The purge gas generated when the desiccant dryer operates in a dual-tower alternating mode also enters buffer tank (III) for recovery, further reducing CO2 emissions. Heat exchanger (II), as a cooling energy recovery heat exchanger, can be of different types, such as plate type or coiled tube type.

[0041] High-purity liquid CO2 in the temporary storage tank is transferred to a large liquid CO2 storage tank for long-term storage. Non-condensable gases from the large liquid CO2 storage tank are then recycled in a buffer tank. The high-purity liquid CO2, after vaporization, can be reinjected into the formation for oil displacement.

[0042] The refrigeration unit provides cooling capacity to the water ring vacuum pump and the all-liquid evaporator, thereby ensuring their normal operation. The compressor in the refrigeration unit can be selected from screw type, centrifugal type, etc., depending on the scale of operation.

[0043] In addition, it is understood that the entire system of the present invention is monitored by an integrated intelligent control system to ensure that each unit operates in coordination, realize automatic adjustment and safety interlock of pressure, flow, temperature and valve opening, and ensure that the entire process is sealed and there is no process gas venting.

[0044] The system process design and control logic in this invention ensure that all process gases are directed to the product outlet or reflux point, with no open venting; it adopts modular and engineering integration, highly integrating complex units, including a simplified PSA regeneration process, into a skid-mounted module, and has been verified in the oilfield.

[0045] The working method of the adaptive variable operating condition oil recovery gas near-zero emission recovery system of the present invention includes the following steps: (1) Associated gas from the oilfield is initially purified by the purification unit to obtain purified gas, which then enters buffer tank 1; (2) Under the stabilizing effect of buffer tank 1 and regulating valve, the pressure swing adsorption device produces natural gas at low pressure according to a specific cycle. The adsorbent is desorbed by the water ring vacuum pump to obtain CO2 enriched gas. (3) The CO2 enriched gas enters the membrane separation and purification unit and is compressed, purified and separated by membrane to obtain high-purity CO2. At the same time, the methane-rich tail gas generated is returned to buffer tank 1. (4) After high-purity CO2 enters the liquefaction unit, it is compressed, purified and cryogenically liquefied to obtain high-purity liquid CO2, which is temporarily stored in a temporary storage tank. The non-condensable gas in the temporary storage tank is recycled and then enters the buffer tank. (5) High-purity CO2 or vaporized liquid CO2 is reinjected into the formation for oil displacement.

[0046] Step (1) is the preliminary purification process. The associated gas from the oilfield passes through the purification unit to remove impurities, sulfides and moisture, and then enters the buffer tank.

[0047] Step (2) is the pressure swing adsorption (PSA) process. Under the rapid stabilizing effect of the buffer tank and the outlet pressure regulating valve, the PSA unit operates according to a specific cycle under the monitoring and command of the intelligent control system. A typical cycle includes: adsorption → equal pressure drop → reverse reduction (reverse release) → vacuum desorption (executed by a water ring vacuum pump) → equal pressure rise → pressurization. Among them, the regeneration process is completed only through the "reverse reduction" and "vacuum desorption" steps, without any purging steps. The system produces qualified low-concentration CO2 (≤4%) natural gas, which enters the CH4 buffer tank, is pressurized, and then outputs. At the same time, CO2-enriched gas is obtained through vacuum desorption.

[0048] Step (3) is the purification process of CO2 enriched gas. The CO2 enriched gas enters the membrane separation and purification unit. After compression, purification and membrane separation, high-purity CO2 product gas is obtained. At the same time, the methane-rich tail gas is returned to the buffer tank for recovery.

[0049] Step (4) is the liquefaction process. High-purity CO2 enters the liquefaction unit and, under the pre-cooling and energy-saving effect of the BOG (non-condensable gas in the temporary storage tank) cold energy recovery heat exchanger II, is compressed, purified, and cryogenically liquefied to obtain high-purity liquid CO2, which is temporarily stored in the temporary storage tank. The non-condensable gas in the temporary storage tank is recovered and then enters the buffer tank III for recovery.

[0050] Step (5) is the utilization process of high-purity CO2 or liquid CO2, which can pressurize the high-purity CO2 gas from the membrane unit or the pressurized liquid CO2 (after vaporization) from the storage tank to the high pressure required by the reservoir and reinject it into the formation for oil displacement.

[0051] The following example, from a pilot-scale test at Shengli Oilfield, will illustrate this point.

[0052] The pilot plant has a processing capacity of 20,000 Nm³. 3The pilot-scale test achieved over 2000 hours of continuous and stable operation, with all units integrated within a skid. A 6-tower VPSA process was employed, using activated carbon and carbon molecular sieves specifically for oil and gas recovery as adsorbents. The operating cycle was: adsorption (420s) - first equalization decrease - second equalization decrease - reverse equalization decrease - vacuum desorption (210s, the tower pressure is reduced to -90kPaG by a water ring vacuum pump) - second equalization increase - first equalization increase - final pressurization. No purging steps were performed throughout the process. The inlet pressure was 0.25-0.55MPaG, CO2 concentration was 35%-90%, and flow rate fluctuated drastically. When pressure fluctuated, the outlet regulating valve responded quickly, stabilizing the tower pressure. The controller adjusted the adsorption time within 200-600s based on the flow rate. The CO2 content of the gas produced by the pressure swing adsorption unit remained stable at 75%-95%; the CO2 purity produced by the membrane separation and purification unit was >95%. BOG cold energy recovery reduces the temperature of the main gas flow before liquefaction by approximately 5°C, and the overall energy consumption of the entire system (including the simplified PSA) is reduced by approximately 20%-25% compared to traditional processes. The entire process is closed-loop with no process gas venting. The simplified regeneration process PSA system and overall process of this invention successfully achieve stable, efficient, low-consumption, and near-zero emission operation in environments with high fluctuations and high concentrations of CO2 produced gas, and has significant potential for large-scale promotion.

[0053] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0054] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0055] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. An adaptive variable-condition oil recovery gas near-zero emission recovery system, characterized in that, include: The associated gas from the oilfield is initially purified in the purification unit to obtain purified gas. The pressure swing adsorption unit is located downstream of the purification unit. The pressure swing adsorption unit includes a buffer tank 1, a pressure swing adsorption device and a water ring vacuum pump arranged sequentially upstream and downstream. The purified gas is adsorbed and separated by the adsorbent in the pressure swing adsorption device to obtain natural gas. The adsorbent is desorbed by the water ring vacuum pump to obtain CO2 enriched gas and stored in the buffer tank 3. The membrane separation and purification unit, located downstream of the pressure swing adsorption unit, allows the CO2-enriched gas in buffer tank three to pass through a first filtration, pressurization, gas-water separation, and a second filtration before entering the membrane unit to obtain high-purity CO2, which is then stored in buffer tank four. The liquefaction unit, located downstream of the membrane separation and purification unit, receives high-purity CO2 from buffer tank four. After being pressurized, separated from water, filtered, and dried, the CO2 enters the all-liquid evaporator to obtain high-purity liquid CO2, which is then stored in a temporary storage tank. A refrigeration unit, which provides cooling capacity for the water ring vacuum pump and the all-liquid evaporator.

2. The system as described in claim 1, characterized in that, A regulating valve and a pressure sensor are installed on the natural gas outlet pipeline of the pressure swing adsorption device. The opening of the regulating valve is adjusted in real time according to the pressure sensor to stabilize the adsorption pressure in the pressure swing adsorption device.

3. The system as described in claim 1, characterized in that, The pressure swing adsorption (PSA) device is equipped with a flow detector at the air inlet of the purified gas. The flow rate of the purified gas is divided into multiple flow ranges according to the flow detector, and the time of each step in the PSA cycle is dynamically adjusted according to the flow range.

4. The system as described in claim 1, characterized in that, The adsorbent includes one of molecular sieves and MOF materials, and the adsorbent selectively separates CO2 and CH4 at 0.25~0.55 MPa.

5. The system as described in claim 1, characterized in that, The purification unit includes a multi-stage pipeline filter, a desulfurization tower, and a refrigerated dryer arranged sequentially upstream and downstream. The associated gas from the oilfield is purified after passing through the multi-stage pipeline filter to remove solid particles and water mist, the desulfurization tower to remove sulfur, and the refrigerated dryer to remove water vapor. The purified gas is then stored in the buffer tank.

6. The system as described in claim 1, characterized in that, The natural gas flows out of the pressure swing adsorption device and enters the second buffer tank. The natural gas in the second buffer tank is pressurized by the booster and then transported to the natural gas recovery station.

7. The system as described in claim 1, characterized in that, The membrane separation and purification unit utilizes a coalescing filter, a first pressurization component, a steam-water separator, and a filter to perform the first filtration, pressurization, steam-water separation, and second filtration processes, respectively. The first pressurization component includes an oil-injected screw compressor, an oil separator, and a heat exchanger arranged sequentially upstream and downstream.

8. The system as described in claim 1, characterized in that, The liquefaction unit utilizes a second pressurization component, a second steam-water separator, a second filter, and a desiccant dryer to perform the pressurization, steam-water separation, filtration, and drying processes. The second pressurization component includes an oil-injected screw compressor, an oil separator, and a heat exchanger arranged sequentially upstream and downstream. When the desiccant dryer operates in a dual-tower alternating mode, the purge gas generated enters the buffer tank. The non-condensable gas in the temporary storage tank enters the buffer tank after its cooling capacity is recovered by the heat exchanger.

9. The system as described in claim 1, characterized in that, The high-purity liquid CO2 in the temporary storage tank enters the large liquid CO2 storage tank, and the non-condensable gas in the large liquid CO2 storage tank enters the buffer tank.

10. A method for operating an adaptive variable-condition oil recovery gas near-zero emission recovery system, characterized in that, The system according to any one of claims 1 to 9 comprises the following steps: Associated gas from the oilfield is initially purified by the purification unit to obtain purified gas, which then enters buffer tank one. Under the stabilizing effect of buffer tank 1 and regulating valve, the pressure swing adsorption unit produces natural gas at low pressure according to a specific cycle. The adsorbent is desorbed by a water ring vacuum pump to obtain CO2 enriched gas. The CO2-enriched gas enters the membrane separation and purification unit, where it is compressed, purified, and separated by a membrane to obtain high-purity CO2. Meanwhile, the methane-rich tail gas generated is returned to buffer tank 1. High-purity CO2 enters the liquefaction unit and is compressed, purified, and cryogenically liquefied to obtain high-purity liquid CO2, which is temporarily stored in a temporary storage tank. The non-condensable gas in the temporary storage tank enters the buffer tank after the recovered cold energy. High-purity CO2 or vaporized liquid CO2 is reinjected into the formation for oil displacement.

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