A system and method for deep decarbonization of high CO2 natural gas PSA

Abstract

This invention discloses a system and method for deep decarbonization of high-CO2 natural gas using a PSA (Pressure Separator) system, relating to the field of oil and gas extraction technology. The invention includes a first-stage PSA decarbonization unit and a second-stage PSA decarbonization unit. The first-stage PSA is used for coarse decarbonization, and the second-stage PSA is used for fine decarbonization, with methane recovery achieved through desorbed gas reflux. The system is equipped with a dynamic rotating dehumidification component, a vacuum desorption structure, and CO2 detection feedback control, enabling intelligent switching and precise control of the adsorption tower. The system adopts a 5-1-2 / VPSA process, using programmable valves to achieve cyclical operations such as adsorption, pressure equalization, and regeneration, offering advantages such as low energy consumption, high methane yield, thorough adsorbent regeneration, and high product gas purity. It is suitable for efficient decarbonization and resource recovery scenarios of high-CO2 natural gas.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, specifically to a system and method for deep decarbonization of high CO2-content natural gas PSA. Background Technology

[0002] With the widespread application of enhanced oil recovery (EOR) technology using gas injection in oil and gas fields, the CO2 content in the natural gas source of recovery projects is gradually increasing, putting enormous pressure on natural gas recovery projects. Currently, traditional natural gas decarbonization technology in natural gas recovery projects generally uses the N-methyldiethanolamine method, but this method is energy-intensive and uneconomical under high CO2 content natural gas conditions. Traditional high CO2 removal methods include pressure swing adsorption (PSA), but the resulting natural gas has a high CO2 content and low methane yield, making it unsuitable for LNG (liquefied natural gas) production. Therefore, there is an urgent need to develop a natural gas CO2 removal technology with high decarbonization accuracy, low methane loss, and adaptability to high CO2 natural gas-to-LNG plants.

[0003] In the field of high CO2 natural gas processing, the pretreatment and drying of feedstock gas is a crucial step in ensuring the stable operation of subsequent decarbonization units. Existing technologies typically employ fixed-bed adsorption dryers filled with solid adsorbents such as molecular sieves or silica gel. However, once the adsorbent becomes saturated, it requires high-temperature regeneration, necessitating a complete shutdown and disrupting the continuity of oil and gas extraction. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides the following technical solution: a system for deep decarbonization of high CO2 natural gas PSA, comprising a first-stage PSA decarbonization unit and a second-stage PSA decarbonization unit. The first-stage PSA decarbonization unit includes a primary compressor, a primary PSA decarbonization unit, and a CO2 detector. A drying component is connected in series between the inlet of the primary compressor and the high CO2 natural gas. The outlet of the primary compressor is connected to the inlet of the primary PSA decarbonization unit. The product gas outlet of the primary PSA decarbonization unit is connected to the inlet of the CO2 detector. The desorbed gas from the primary PSA decarbonization unit is vented to a venting unit for venting treatment.

[0005] The two-stage PSA decarbonization unit includes a two-stage compressor and a two-stage PSA decarbonization unit; the inlet of the two-stage compressor is connected to the outlet of the CO2 detector, the outlet of the two-stage compressor is connected to the inlet of the two-stage PSA decarbonization unit, the product gas of the two-stage PSA decarbonization unit goes to the subsequent dehydration and mercury removal unit, and the desorbed gas returns to the inlet of the first-stage compressor to recover the methane in the desorbed gas.

[0006] Preferably, the drying assembly includes a base frame, on which a fixed flow guide ring groove is fixedly installed. A moving flow guide ring groove is rotatably sealed on the fixed flow guide ring groove. A collector is disposed at the axial position inside the moving flow guide ring groove. The collector and the moving flow guide ring groove are connected by multiple refrigerant guide pipes arranged radially along the moving flow guide ring groove. The inner wall surface of each refrigerant guide pipe is uniformly provided with multiple temperature-conducting strips arranged in a circular array.

[0007] Preferably, a first refrigerant connection port and a second refrigerant connection port are also fixedly installed on the base frame. The first refrigerant connection port is connected to the inside of the fixed flow guide ring groove, and the second refrigerant connection port is connected and cooperated with the manifold rotary seal.

[0008] Preferably, all refrigerant drain pipes are embedded inside the rotating seat, which is rotatably positioned inside the fixed flow guide annular groove. A condenser fin assembly is fixedly installed on the upper surface of the rotating seat, and all fins in the condenser fin assembly are fixedly connected to each other via heat pipes.

[0009] Preferably, a conical shroud is coaxially sleeved on the outer side of the condenser fin assembly, and a gap is provided between the inner wall of the conical shroud and the condenser fin assembly. The top of the conical shroud is rotatably fitted with the top of the condenser fin assembly. An opening is provided at the center of the top of the conical shroud, and a drive impeller is rotatably installed in the opening. The drive impeller is fixedly fitted with the condenser fin assembly.

[0010] Preferably, a flow guide cover is fixedly installed on the base frame, and the flow guide cover is rotary sealed with the moving flow guide ring groove and the rotating seat; the conical flow guide cover is fixedly fitted with the flow guide cover; a gap is left between the bottom edge of the conical flow guide cover and the rotating seat; the bottom of the flow guide cover is fixedly connected to a water storage tank through a drainage channel; the bottom of the water storage tank is equipped with a drainage pipe, and an electric valve is installed inside the drainage pipe.

[0011] Preferably, an air inlet port is fixedly connected to the top of the flow guide shroud at a position aligned with the drive impeller, and the air inlet port is connected to the interior of the conical flow guide shroud. An exhaust port is provided at the top of the flow guide shroud at a position between the inner wall of the flow guide shroud and the outer surface of the conical flow guide shroud.

[0012] A method for deep decarbonization of high-CO2 natural gas PSA includes the following steps: Step 1: The high-CO2 natural gas is first subjected to condensation and dehumidification treatment by a drying assembly. The refrigerant circulation and the rotating condenser fins condense and collect the moisture in the natural gas, reducing its water content to prevent icing in subsequent equipment or adsorbent failure. Step 2: The dried high-CO2 natural gas enters a primary compressor for pressurization. The inlet pressure is controlled at 100 kPa to 0.5 MPa, the exhaust pressure at 1 to 2 MPa, the inlet temperature at 20 to 40°C, and the exhaust temperature at less than 120°C. Step 3: The pressurized high-CO2 natural gas enters the primary PSA decarbonization unit, which includes five or more adsorption towers. Each tower alternates between adsorption and regeneration under the control of a programmable valve. Coarse CO2 removal is achieved through a 5-1-2 / VPSA cycle. The desorbed gas from the primary PSA decarbonization unit is high-concentration CO2 gas and is sent to the venting unit. Step 4: A CO2 detector is installed at the product gas outlet of the primary PSA decarbonization unit to monitor the CO2 content in the product gas in real time and feeds the results back to the secondary PSA decarbonization unit. The programmable control system of the PSA decarbonization unit provides a basis for the automatic adjustment of adsorption time, switching cycle, and operating pressure of the subsequent adsorption towers; Step 5: The primary PSA decarbonization product gas, after testing, enters the secondary compressor through the CO2 detector outlet, where it is pressurized to 3-5 MPa. The inlet temperature is controlled at 20-40℃, and the exhaust temperature is less than 120℃ to meet the operating conditions for deep decarbonization of the secondary PSA decarbonization unit; Step 6: The secondary PSA decarbonization unit is equipped with five or more adsorption towers, which alternately perform adsorption and regeneration under the control of programmable valves, based on the real-time detection data of the CO2 detector. The adsorption time and pressure are dynamically adjusted to achieve deep decarbonization. The desorbed gas in the secondary PSA decarbonization unit is mainly CO2 and a small amount of methane. It is returned to the inlet of the primary compressor through the pipeline to achieve methane recovery and reduce methane loss. In step 7, the adsorption towers of the primary PSA decarbonization unit and the secondary PSA decarbonization unit are alternately subjected to adsorption, two pressure equalization, reverse release, vacuuming, two pressure equalization and final pressure increase operations according to the 5-1-2 / VPSA cycle process. The adsorbent is completely regenerated by deep vacuuming through a water ring vacuum pump, thereby achieving continuous decarbonization operation of natural gas with high CO2 content and high-purity output of purified gas.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention sets up a two-stage PSA decarbonization unit and sets up a return line in the two-stage desorption gas path so that the desorption gas returns to the inlet of the first-stage compressor, thereby realizing the recovery of methane in the desorption gas. This design effectively reduces the direct venting loss of methane in the "dead space" during the desorption process, and significantly improves the methane yield. Compared with single-stage PSA, the methane loss is reduced by more than 50%, which not only improves resource utilization but also reduces the economic and environmental losses caused by gas venting; (2) The secondary PSA decarbonization unit of this invention operates under high pressure and uses the 5-1-2 / VPSA process to achieve deep decarbonization. In addition, the CO2 detector adjusts the adsorption time and switching rhythm in real time, so that CO2 is fully removed in the second adsorption stage, ensuring that the CO2 content of the natural gas after decarbonization is stable in the range of ≤0.1%~0.3%, which is significantly better than the residual level of single-stage PSA and meets the requirements of subsequent dehydration and mercury removal units and downstream LNG processes; (3) Both the primary and secondary PSA units of this invention can automatically increase or decrease the number of adsorption towers according to the natural gas flow rate, and form a closed-loop control through programmable valves and CO2 detectors to achieve automatic adjustment of adsorption cycle, pressure and regeneration rhythm, thereby maintaining high and stable decarbonization performance under different gas source flow rates and different CO2 concentrations; (4) The drying component of this invention uses condenser fin groups and refrigerant loops to achieve high-speed rotation dehumidification, with a compact structure and sufficient heat exchange. The condensate is discharged through centrifugal separation and automatic level control, which can effectively prevent moisture from entering the compressor intake, improve the service life of the compressor and adsorbent, and eliminate the need for high-temperature regeneration after the adsorbent is saturated, thus ensuring the continuity of oil and gas extraction. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of the present invention.

[0015] Figure 2 This is a structural diagram of the drying component of the present invention.

[0016] Figure 3 This is a structural diagram of the internal structure of the flow guide cover of the present invention.

[0017] Figure 4 This is a structural diagram of the condenser fin assembly of the present invention.

[0018] Figure 5 This is a diagram showing the distribution of the refrigerant drainage pipes in this invention.

[0019] Figure 6 This is a cross-sectional view of the fixed flow guide ring groove structure of the present invention.

[0020] Figure 7 For the present invention Figure 6 Enlarged view of point A in the middle.

[0021] In the diagram: 1-First-stage compressor; 2-First-stage PSA decarbonization unit; 3-CO2 detector; 4-Second-stage compressor; 5-Second-stage PSA decarbonization unit; 6-Drying assembly; 601-Base frame; 602-Guide cover; 603-Exhaust port; 604-Inlet port; 605-Drive impeller; 606-Conical guide shroud; 607-Drainage channel; 608-Water storage tank; 609-Drainage pipe; 610-Condenser fin assembly; 611-Heat pipe; 612-Fixed guide ring groove; 613-Moving guide ring groove; 614-First refrigerant connection port; 615-Second refrigerant connection port; 616-Rotating seat; 617-Refrigerant guide pipe; 618-Collection stream; 619-Temperature guide strip; 7-Dehydration and mercury removal unit; 8-Ventilation unit. Detailed Implementation

[0022] The following is in conjunction with the appendix Figures 1-7 The technical solution of the present invention will be further illustrated through specific embodiments.

[0023] This invention provides a system for deep decarbonization of high-CO2 natural gas PSA, comprising a first-stage PSA decarbonization unit and a second-stage PSA decarbonization unit. The first-stage PSA decarbonization unit includes a primary compressor 1, a primary PSA decarbonization unit 2, and a CO2 detector 3. A drying assembly 6 is connected in series between the inlet of the primary compressor 1 and the high-CO2 natural gas. The outlet of the primary compressor 1 is connected to the inlet of the primary PSA decarbonization unit 2, and the product gas outlet of the primary PSA decarbonization unit 2 is connected to the inlet of the CO2 detector 3. The desorbed gas from the primary PSA decarbonization unit 2 is vented to a venting unit 8 for venting treatment. The second-stage PSA decarbonization unit includes a secondary compressor 4 and a secondary PSA decarbonization unit 5. The inlet of the secondary compressor 4 is connected to the outlet of the CO2 detector 3, and the outlet of the secondary compressor 4 is connected to the inlet of the secondary PSA decarbonization unit 5. The product gas from the secondary PSA decarbonization unit 5 is sent to a subsequent dehydration and mercury removal unit 7, and the desorbed gas is returned to the inlet of the primary compressor 1 to recover methane from the desorbed gas. The first-stage compressor 1 pressurizes the high-CO2-content natural gas to provide pressure for the initial CO2 removal in the first-stage PSA decarbonization unit 2. The first-stage PSA decarbonization unit 2 is equipped with five or more adsorption towers, which can be adjusted according to the natural gas flow rate to accommodate different flow rates. The adsorption towers within the first-stage PSA decarbonization unit 2 are intelligently controlled by programmable valves, allowing for alternating adsorption and regeneration, thus achieving continuous separation and purification of the natural gas. The first-stage PSA decarbonization unit 2 performs initial decarbonization of the high-CO2-content natural gas, and the desorbed gas from this unit is primarily CO2, entering the venting unit 8. A CO2 detector 3 is installed at the product gas outlet of the first-stage PSA decarbonization unit 2 to monitor the CO2 content in the product gas in real time, providing parameters for the automatic adjustment of the second-stage PSA decarbonization unit 5. The second-stage compressor 4 pressurizes the product gas from the first-stage PSA decarbonization unit to meet the fine decarbonization requirements of the second-stage PSA decarbonization unit 5. The secondary PSA decarbonization unit 5 is equipped with five or more adsorption towers, which can be increased or decreased according to the natural gas flow rate to adapt to different flow rates of natural gas for decarbonization treatment. The adsorption towers within the secondary PSA decarbonization unit 5 are connected by programmable valves. These valves automatically adjust the adsorption time based on the results from the CO2 detector 3, improving the decarbonization efficiency of the secondary PSA decarbonization unit 5. Intelligent control allows each adsorption tower to alternately adsorb and regenerate, achieving continuous separation and purification of natural gas. The secondary PSA decarbonization unit 5 performs fine decarbonization treatment on the product gas from the primary PSA decarbonization unit. The desorbed gas from the secondary PSA decarbonization unit 5 mainly consists of CO2 and methane. The desorbed gas is returned via pipeline to the inlet of the primary compressor 1 to recover methane and reduce methane loss.

[0024] The drying assembly 6 includes a base frame 601, on which a fixed flow guide annular groove 612 is fixedly mounted. A movable flow guide annular groove 613 is rotary-sealed on the fixed flow guide annular groove 612. A collector 618 is located at the axial center of the inner side of the movable flow guide annular groove 613. The collector 618 and the movable flow guide annular groove 613 are connected by multiple refrigerant guide pipes 617 arranged radially along the movable flow guide annular groove 613. The inner wall surface of each refrigerant guide pipe 617 is uniformly provided with multiple circularly arranged temperature-conducting strips 619. A first refrigerant connection port 614 and a second refrigerant connection port 615 are also fixedly mounted on the base frame 601. The first refrigerant connection port 614 is connected to the inside of the fixed flow guide annular groove 612, and the second refrigerant connection port 615 is rotary-sealed and connected to the collector 618. All refrigerant guide pipes 617 are embedded inside a rotating seat 616, which is rotatably positioned inside a fixed flow guide annular groove 612. A condenser fin assembly 610 is fixedly mounted on the upper surface of the rotating seat 616, and all fins in the condenser fin assembly 610 are fixedly engaged with each other via heat pipes 611. A conical flow guide shroud 606 is coaxially fitted on the outer side of the condenser fin assembly 610, with a gap between the inner wall of the conical flow guide shroud 606 and the condenser fin assembly 610. The top of the conical flow guide shroud 606 is rotatably engaged with the top of the condenser fin assembly 610. An opening is provided at the center of the top of the conical flow guide shroud 606, and a drive impeller 605 is rotatably mounted in the opening, which is fixedly engaged with the condenser fin assembly 610. A flow guide cover 602 is fixedly mounted on the base frame 601. The flow guide cover 602 is rotary sealed with the moving flow guide ring groove 613 and the rotating seat 616. A conical flow guide cover 606 is fixedly fitted with the flow guide cover 602. A gap is left between the bottom edge of the conical flow guide cover 606 and the rotating seat 616. A water storage tank 608 is fixedly connected to the bottom of the flow guide cover 602 through a drainage channel 607. A drainage pipe 609 is provided at the bottom of the water storage tank 608, and an electric valve is installed inside the drainage pipe 609. An air inlet port 604 is fixedly connected to the top of the flow guide cover 602 at a position aligned with the drive impeller 605, and the air inlet port 604 is connected to the inside of the conical flow guide cover 606. An exhaust port 603 is provided at the top of the flow guide cover 602 at a position between the inner wall of the flow guide cover 602 and the outer surface of the conical flow guide cover 606.

[0025] High-CO2 natural gas passes through the drying assembly 6 and enters the first-stage compressor 1 for pressurization. This high-CO2 natural gas then enters the conical shroud 606 through the inlet port 604, bringing it into contact with the condenser fin assembly 610. Simultaneously, the flowing high-CO2 natural gas drives the impeller 605 to rotate, which in turn drives the condenser fin assembly 610 to rotate. The rotation of the condenser fin assembly 610 then drives the rotating seat 616 and all the refrigerant guide pipes 617 to rotate. Prior to this, the refrigerant needs to be connected to the first refrigerant connection port 614 and the second refrigerant connection port 615, allowing the refrigerant to circulate among the first refrigerant connection port 614, the fixed guide ring groove 612, the moving guide ring groove 613, the refrigerant guide pipes 617, the manifold 618, and the second refrigerant connection port 615. Finally, the condenser fin assembly 610 is cooled to a low temperature, which facilitates the condensation of moisture in the high CO2 content natural gas onto the condenser fin assembly 610, thereby reducing the water content of the high CO2 content natural gas and facilitating subsequent decarbonization treatment. During this process, the high CO2 content natural gas is finally discharged into the guide shroud 602 through the bottom of the condenser fin assembly 610, and then transported to the inlet of the first-stage compressor 1 through the exhaust port 603. Water droplets condensed on the condenser fin assembly 610 will rotate along with the condenser fin assembly 610. The rotating water droplets will move towards the inner wall of the conical drainage hood 606 under centrifugal force, eventually separating from the condenser fin assembly 610 and falling into the bottom of the guide hood 602 under the protection of the conical drainage hood 606, and finally sliding into the water storage tank 608. The water storage tank 608 is equipped with a liquid level sensor. When the water level inside the water storage tank 608 reaches the set value, the electric valve inside the drain pipe 609 is activated to drain the water inside the water storage tank 608, and then the electric valve is closed. When the refrigerant passes through the refrigerant inlet pipe 617, it comes into contact with the internal temperature-conducting strip 619. This causes the refrigerant near the inner wall of the refrigerant inlet pipe 617 to experience resistance from the temperature-conducting strip 619, resulting in a reduced flow rate. Meanwhile, the refrigerant at the axis of the refrigerant inlet pipe 617 flows normally. Therefore, the flow rate of the refrigerant at the inner wall of the refrigerant inlet pipe 617 is lower than that at the axis. This causes the refrigerant at the edge of the inner wall of the refrigerant inlet pipe 617 to flow towards the axis, thus forming an annular vortex. The annular vortex causes the refrigerant at the inner wall of the refrigerant inlet pipe 617 to alternate with the refrigerant at the axis of the refrigerant inlet pipe 617 (resulting in a more uniform distribution), thereby increasing the rate at which the refrigerant absorbs heat from the refrigerant inlet pipe 617.

[0026] The overall workflow is as follows: Step 1: High-CO2 natural gas first undergoes condensation and dehumidification treatment via drying component 6. Utilizing refrigerant circulation and the rotating condenser fins, the moisture in the natural gas is condensed, collected, and discharged, reducing the water content to prevent icing in subsequent equipment or adsorbent failure. Step 2: The dried high-CO2 natural gas enters the first-stage compressor 1 for pressurization. The inlet pressure is controlled at 100 kPa to 0.5 MPa, the exhaust pressure at 1 to 2 MPa, the inlet temperature at 20 to 40°C, and the exhaust temperature at less than 120°C. This is the adsorption process for the first-stage PSA decarbonization unit 2. The process provides the required pressure conditions; Step 3: The pressurized high-CO2 natural gas enters the first-stage PSA decarbonization unit 2, which includes five or more adsorption towers. Each adsorption tower alternates between adsorption and regeneration under the control of a programmable valve, achieving coarse CO2 removal through a 5-1-2 / VPSA cycle. The desorbed gas from the first-stage PSA decarbonization unit 2 is high-concentration CO2 gas and is sent to the venting unit 8; Step 4: A CO2 detector 3 is installed at the product gas outlet of the first-stage PSA decarbonization unit 2 to detect the CO2 content in the product gas in real time and feed the detection results back to the programmable control system of the second-stage PSA decarbonization unit 5. This system provides a basis for the automatic adjustment of adsorption time, switching cycle, and operating pressure of the subsequent adsorption towers; Step 5: The first-stage PSA decarbonization product gas, after testing, enters the second-stage compressor 4 through the outlet of the CO2 detector 3, where it is pressurized to 3-5 MPa. The inlet temperature is controlled at 20-40℃, and the exhaust temperature is less than 120℃ to meet the operating conditions for deep decarbonization of the second-stage PSA decarbonization unit 5; Step 6: The second-stage PSA decarbonization unit 5 is equipped with five or more adsorption towers, which alternately perform adsorption and regeneration under the control of programmable valves, and automatically adjust the adsorption based on the real-time detection data of the CO2 detector 3. With time and pressure, deep decarbonization is achieved; the desorbed gas of the secondary PSA decarbonization unit 5 is mainly CO2 and a small amount of methane, which is returned to the inlet of the primary compressor 1 through the pipeline to achieve methane recovery and reduce methane loss; in step 7, the adsorption towers of the primary PSA decarbonization unit 2 and the secondary PSA decarbonization unit 5 are both subjected to adsorption, two pressure equalization, reverse release, vacuuming, two pressure equalization and final pressure increase operations in an alternating 5-1-2 / VPSA cycle process. The adsorbent is completely regenerated by deep vacuuming through a water ring vacuum pump, thereby achieving continuous decarbonization operation of natural gas with high CO2 content and high-purity output of purified gas.

[0027] Internal process description of primary PSA decarbonization unit 2 and secondary PSA decarbonization unit 5 (taking 5 adsorption towers as an example):

[0028] Both the primary PSA decarbonization unit 2 and the secondary PSA decarbonization unit 5 adopt a 5-1-2 / VPSA (Variable Pressure Swing Adsorption) process, which consists of five adsorption towers. One tower performs adsorption, followed by two pressure equalization cycles and vacuum regeneration. The adsorbent saturated with CO2 undergoes two pressure equalization cycles, reverse release, vacuuming, two pressure equalization cycles, and a final pressure increase to complete a full "adsorption-regeneration" cycle, preparing for the next adsorption cycle. Each adsorption tower alternates between adsorption and regeneration processes, achieving continuous separation and purification of high-CO2 natural gas (while maintaining one tower at a time). This process can be divided into the following steps:

[0029] Adsorption process: High-CO2 natural gas enters the pre-adsorption tower from the bottom. Inside the tower, the adsorbent adsorbs CO2 and other impurities under high pressure. Unadsorbed methane and other impurities flow out from the top of the tower as product gas, entering the product gas buffer tank and then proceeding to subsequent units. After the adsorption process is complete, the adsorption tower enters the regeneration stage.

[0030] Pressure equalization and depressurization process: After adsorption is completed, the high-pressure gas in the adsorption tower is transferred to other low-pressure adsorption towers that have completed regeneration in the direction of adsorption. At the same time, the effective gas in the dead space of the bed is recovered to improve the yield of methane.

[0031] Reverse release process: After the pressure equalization and depressurization process is completed, the pressure is reduced in the opposite direction of adsorption in the adsorption tower, so that the adsorbed CO2 is desorbed. The desorbed gas from the first-stage PSA decarbonization unit 2 goes to the venting unit 8, and the desorbed gas from the second-stage PSA decarbonization unit 5 returns to the inlet of the first-stage compressor.

[0032] Vacuuming process: After the reverse release process, the pressure is further reduced by evacuating the vacuum pump, so that CO2 is completely desorbed, achieving the purpose of adsorbent regeneration. The desorbed gas goes to the same destination as the reverse release process. The vacuum pump is a water ring vacuum pump, powered by circulating water.

[0033] Pressure equalization and pressurization process: Higher pressure gas from other adsorption towers is used to sequentially pressurize the adsorption tower, restoring the pressure inside the tower to the normal operating pressure and preparing for the next adsorption cycle. Simultaneously, the pressurization process also helps recover methane from the dead space of other adsorption tower beds, increasing methane yield.

[0034] Product gas pressurization process: After the pressure equalization and pressurization process is completed, in order to ensure that the adsorption tower can smoothly switch to the next adsorption cycle, the pressure of the adsorption tower is slowly and steadily increased to the adsorption pressure by using product gas through a programmable valve.

[0035] After the above series of processes, the adsorption tower completes a full "adsorption-regeneration" cycle, and is also ready for the next adsorption cycle.

[0036] The primary compressor has an inlet pressure range of 100 kPa to 0.5 MPa, an exhaust pressure of 1 to 2 MPa, an inlet temperature of 20 to 40°C, and an exhaust temperature of <120°C. This equipment provides the pressure conditions for the first-stage PSA decarbonization, and the temperature needs to be controlled to prevent gas overheating. The operating pressure of the first-stage PSA decarbonization unit is 0.5 to 2 MPa, and the operating temperature is 20 to 90°C. This unit is for preliminary CO2 removal (coarse removal), and the selected adsorbent is suitable for this pressure range. The CO2 detector has a detection range of 0 to 3000 ppm and a detection accuracy of ±2%FS. It also has strong anti-interference capabilities, effectively avoiding the influence of background gases (such as methane, nitrogen, etc.) on CO2 measurement results; the inlet pressure of the secondary compressor is 0.5~2MPa, the exhaust pressure is 3~5MPa, the inlet temperature is 20~40℃, and the exhaust temperature is <120℃. This equipment provides pressure conditions for the two-stage PSA decarbonization, meeting the requirements for deep decarbonization; the operating pressure of the two-stage PSA decarbonization unit is 3~5MPa, and the operating temperature is 20~90℃. This equipment unit is for deep CO2 removal (fine removal), ensuring the purity of the purified gas in subsequent processing units.

[0037] Compared to MDEA decarbonization, which is a chemical absorption process, methane has low solubility in MDEA solution and is essentially not absorbed, resulting in a higher yield. However, this method suffers from high regeneration energy consumption and flooding issues during adsorption in the absorption tower when processing natural gas with high CO2 content. In single-stage PSA decarbonization, a significant amount of methane gas remains in the adsorbent residue (dead space) during desorption and is directly emitted as waste gas, leading to a low methane yield. Furthermore, this process involves high-pressure adsorption and low-pressure desorption; the adsorbent also adsorbs some methane during high-pressure adsorption, further reducing the methane yield. Two-stage PSA decarbonization, through two-stage pressurization and PSA adsorption, achieves higher overall efficiency. A vacuum pump is added to deeply evacuate the adsorption tower after atmospheric desorption, maximizing the separation of methane and adsorbed carbon dioxide from the dead space. Simultaneously, a desorption gas reflux line is implemented to return the second-stage PSA desorption gas to the inlet of the first-stage compressor, significantly reducing methane loss and achieving a high methane yield. Furthermore, thanks to deep vacuum desorption, the adsorbent regeneration is more thorough, and the adsorption capacity is larger, resulting in higher purity purified gas. The CO2 content in the purified gas can be stably controlled within the range of ≤0.1%-0.3%, meeting the requirements of subsequent treatment stages. Therefore, two-stage PSA decarbonization is more suitable for treating high-CO2 natural gas.

Claims

1. A system for deep decarbonization of high CO2-content natural gas PSA, characterized in that: It includes a first-stage PSA decarbonization unit and a second-stage PSA decarbonization unit. The first-stage PSA decarbonization unit includes a first-stage compressor (1), a first-stage PSA decarbonization unit (2), and a CO2 detector (3). A drying component (6) is connected in series between the inlet of the first-stage compressor (1) and the connection between the high CO2-content natural gas and the outlet of the first-stage compressor (1). The product gas outlet of the first-stage PSA decarbonization unit (2) is connected to the inlet of the CO2 detector (3). The desorbed gas of the first-stage PSA decarbonization unit (2) is vented to the venting unit (8) for venting treatment. The two-stage PSA decarbonization unit includes a two-stage compressor (4) and a two-stage PSA decarbonization unit (5); the inlet of the two-stage compressor (4) is connected to the outlet of the CO2 detector (3), the outlet of the two-stage compressor (4) is connected to the inlet of the two-stage PSA decarbonization unit (5), the product gas of the two-stage PSA decarbonization unit (5) goes to the subsequent dehydration and mercury removal unit (7), and the desorbed gas returns to the inlet of the first-stage compressor (1) to recover the methane in the desorbed gas; The drying assembly (6) includes a moving flow guide ring groove (613). A collector (618) is provided at the axial position inside the moving flow guide ring groove (613). The collector (618) and the moving flow guide ring groove (613) are connected by multiple refrigerant guide pipes (617) arranged radially along the moving flow guide ring groove (613). The inner wall surface of each refrigerant guide pipe (617) is uniformly provided with multiple circular array of temperature-conducting strips (619). All the refrigerant guide pipes (617) are embedded in the rotating seat (616). A condenser fin assembly (610) is fixedly installed on the upper surface of the rotating seat (616). The drying assembly (6) also includes a base frame (601), a fixed flow guide ring groove (612) is fixedly installed on the base frame (601), and the fixed flow guide ring groove (612) and the moving flow guide ring groove (613) are rotary sealed together; a first refrigerant connection port (614) and a second refrigerant connection port (615) are also fixedly installed on the base frame (601), the first refrigerant connection port (614) is connected to the inside of the fixed flow guide ring groove (612), and the second refrigerant connection port (615) is rotary sealed together with the manifold (618). The rotating seat (616) is rotatably mounted inside the fixed flow guide ring groove (612), and all the fins in the condenser fin assembly (610) are fixedly connected by heat pipes (611); a conical flow guide shroud (606) is coaxially sleeved on the outer side of the condenser fin assembly (610), and there is a gap between the inner wall of the conical flow guide shroud (606) and the condenser fin assembly (610), and the top of the conical flow guide shroud (606) is rotatably connected to the top of the condenser fin assembly (610); an opening is provided at the center of the top of the conical flow guide shroud (606), and a drive is rotatably installed in the opening. A moving impeller (605) is fixedly fitted with a condenser fin assembly (610); a flow guide cover (602) is fixedly installed on a base frame (601), and the flow guide cover (602) is rotaryly sealed with a moving flow guide ring groove (613) and a rotating seat (616); a conical flow guide cover (606) is fixedly fitted with the flow guide cover (602); a gap is left between the bottom edge of the conical flow guide cover (606) and the rotating seat (616), and the bottom of the flow guide cover (602) is fixedly connected to a drainage channel (607). A water storage tank (608) is provided with a drainage pipe (609) at the bottom of the water storage tank (608), and an electric valve is provided inside the drainage pipe (609); an air inlet port (604) is fixedly connected to the top of the flow guide cover (602) at the position aligned with the drive impeller (605), and the air inlet port (604) is connected to the inside of the conical flow guide cover (606). An exhaust port (603) is provided at the top of the flow guide cover (602) at the position between the inner wall of the flow guide cover (602) and the outer surface of the conical flow guide cover (606).

2. A method for deep decarbonization of high-CO2-content natural gas PSA, using the system for deep decarbonization of high-CO2-content natural gas PSA as described in claim 1, characterized in that, Includes the following steps: Step 1: High CO2 natural gas is first condensed and dehumidified by the drying component (6). The refrigerant circulation and the condensation fin assembly are used to condense and collect the moisture in the natural gas and discharge it, thereby reducing the water content to prevent subsequent equipment from freezing or the adsorbent from failing. Step 2: The dried high CO2 natural gas enters the first-stage compressor (1) for pressurization. The inlet pressure is controlled at 100KPa~0.5MPa, the exhaust pressure is 1~2MPa, the inlet temperature is 20~40℃, and the exhaust temperature is less than 120℃, so as to provide the required pressure conditions for the adsorption process of the first-stage PSA decarbonization unit (2). Step 3: The pressurized high CO2 natural gas enters the first-stage PSA decarbonization unit (2). This unit includes more than five adsorption towers. Each adsorption tower alternates adsorption and regeneration under the control of a programmable valve. The coarse removal of CO2 is achieved through the 5-1-2 / VPSA cycle process, that is, 5 towers are in operation, 1 tower is adsorbed, 2 pressure equalizations are performed, and vacuum regeneration is performed. The desorbed gas of the first-stage PSA decarbonization unit (2) is high-concentration CO2 gas and is sent to the venting unit (8). Step 4: A CO2 detector (3) is installed at the product gas outlet of the primary PSA decarbonization unit (2) to detect the CO2 content in the product gas in real time and feed the detection results back to the programmable control system of the secondary PSA decarbonization unit (5) to provide a basis for the automatic adjustment of the adsorption time, switching cycle and operating pressure of the adsorption tower in the subsequent process. Step 5: After testing, the first-stage PSA decarbonization product gas enters the second-stage compressor (4) through the outlet of the CO2 detector (3). In the second-stage compressor (4), the pressure is increased to 3-5 MPa, the inlet temperature is controlled at 20-40℃, and the exhaust temperature is less than 120℃, so as to meet the operating conditions of deep decarbonization of the second-stage PSA decarbonization unit (5). Step 6: The secondary PSA decarbonization unit (5) is equipped with more than five adsorption towers, which alternately perform adsorption and regeneration under the control of the programmable valve. The adsorption time and pressure are automatically adjusted according to the real-time detection data of the CO2 detector (3) to achieve deep decarbonization. The desorbed gas of the secondary PSA decarbonization unit (5) is mainly CO2 and a small amount of methane. It is returned to the inlet of the primary compressor (1) through the pipeline to achieve methane recovery and reduce methane loss. Step 7: The adsorption towers of the primary PSA decarbonization unit (2) and the secondary PSA decarbonization unit (5) are both subjected to adsorption, two equalization pressure, reverse release, vacuuming, two equalization pressure increases and final pressure increase in an alternating 5-1-2 / VPSA cycle process. The adsorbent is completely regenerated by deep vacuuming through a water ring vacuum pump, thereby achieving continuous decarbonization operation of natural gas with high CO2 content and high-purity output of purified gas.

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