Propylene recovery system
The propylene recovery system, which combines compression condensation and two-stage membrane modules, solves the problem of propylene resource waste during the start-up and shutdown of propylene polymerization and separation units, achieving efficient recovery of propylene and nitrogen and reducing economic losses and environmental pollution.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUATING COAL GRP CO LTD
- Filing Date
- 2026-06-08
- Publication Date
- 2026-08-04
AI Technical Summary
The lack of effective means in the current technology to recover planned emissions from propylene polymerization and separation units during start-up and shutdown leads to waste of propylene resources and environmental pollution.
A propylene recovery system employing a combination of compression and condensation with two-stage membrane modules is used. The compression module increases the pressure of the gaseous mixed medium, the condensation module condenses the gaseous propylene into a liquid state, the separator separates the liquid propylene, and the two-stage membrane modules further separate and enrich the propylene. Uncondensed gas is recycled, and nitrogen is retained and reused.
This improved the propylene recovery rate, reduced propylene emissions, lowered economic losses and environmental burden, and achieved efficient recycling and utilization of propylene and nitrogen.
Smart Images
Figure CN122499609A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of membrane separation technology, and specifically relates to a propylene recovery system. Background Technology
[0002] During start-up and shutdown of propylene polymerization units, propylene separation units, and other related units, nitrogen is often used in the propylene gas replacement system, and the mixed gas is then discharged into the flare system. The amount of propylene gas emitted annually during start-up and shutdown is considerable, resulting not only in raw material waste and economic losses, but also in the environmental burden caused by the large amount of carbon dioxide produced when propylene is burned in the flare. Current technologies lack effective recovery methods for such planned emissions, and most of the gas is directly burned in the flare, resulting in low resource utilization. Summary of the Invention
[0003] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a propylene recovery system capable of automatically recovering propylene from a mixture of propylene and nitrogen.
[0004] The propylene recovery system of this invention includes an inlet system, a compression assembly, a condensation assembly, a separator, and a first membrane assembly and a second membrane assembly connected in series. The inlet system is used to introduce a gaseous mixed medium, which includes gaseous propylene and / or nitrogen. The inlet of the compression assembly is connected to the inlet system to increase the pressure of the gaseous mixed medium. The inlet of the condensation assembly is connected to the outlet of the compression assembly to condense the gaseous propylene in the gaseous mixed medium into liquid propylene. The inlet of the separator is connected to the outlet of the condensation assembly to separate the liquid propylene. Both the first membrane assembly and the second membrane assembly include an inlet, a retardation-side outlet, and a permeation-side outlet. The inlet of the first membrane assembly is connected to the gas phase outlet of the separator, the retardation-side outlet of the first membrane assembly is connected to the inlet of the second membrane assembly, the permeation-side outlet of the first membrane assembly is connected to the inlet of the compression assembly, the permeation-side outlet of the second membrane assembly is connected to a flare system, and the retardation-side outlet of the second membrane assembly is connected to a nitrogen recovery device.
[0005] The propylene recovery system of this invention utilizes compression condensation combined with a two-stage membrane module connected in series, returning the permeate from the first membrane module to the inlet of the compression module, to recycle and recover propylene from the gaseous mixture. Uncondensed gas is further enriched with propylene via membrane separation and then sent back to the front end for reprocessing, while nitrogen is recovered on the retaining side of the second membrane module. This system reduces the amount of propylene emitted to the flare and recovers nitrogen for reuse, helping to reduce economic losses and environmental burden during plant start-up and shutdown.
[0006] In some embodiments, the condensation assembly includes a first condenser and a second condenser connected in series; both the first condenser and the second condenser include a refrigerant passage and a process gas passage, wherein the refrigerant passage is used for the flow of refrigerant, the process gas passage is used for the flow of the gaseous mixed medium, and the outlet of the process gas passage of the second condenser is connected to the separator, wherein the temperature of the refrigerant used in the second condenser is lower than the temperature of the refrigerant used in the first condenser.
[0007] In some embodiments, the second condenser further includes a gas phase delivery channel, the inlet end of which is connected to the gas phase outlet of the separator, and the outlet end of which is connected to the inlet of the first membrane module. The gas phase delivery channel is used to recover the cooling capacity of the gaseous mixed medium flowing inside it.
[0008] In some embodiments, the propylene recovery system further includes a first pipe, a second pipe, a first valve disposed on the first pipe, and a second valve disposed on the second pipe; one end of the first pipe is connected to the outlet end of the gas phase conveying channel, and the other end is connected to the flare system; one end of the second pipe is connected to the outlet end of the gas phase conveying channel, and the other end is connected to the inlet of the first membrane module.
[0009] In some embodiments, the propylene recovery system further includes a pressure detection component and a control system; the pressure detection component is located at the gas phase outlet of the separator and is electrically connected to the control system, for detecting the pressure at the gas phase outlet of the separator and feeding back the pressure signal to the control system; the control system is electrically connected to both the first valve and the second valve, and the control system is used to control one of the first valve and the second valve to open and the other to close according to the feedback information from the pressure detection component.
[0010] In some embodiments, the propylene recovery system further includes a filter assembly, the inlet of which is connected to the air intake system and the outlet of which is connected to the inlet of the compression assembly, for filtering solid impurities in the gaseous mixture.
[0011] In some embodiments, the air intake system includes multiple parallel process pipelines, each of which is equipped with a switch valve. At least a portion of the process pipelines are used to connect to a nitrogen unit and a process gas unit, respectively, and at least a portion of the process pipelines are used to connect to a propylene polymerization unit and / or a propylene separation unit.
[0012] In some embodiments, the compression assembly includes a screw compressor and an intake buffer tank, the inlet of the intake buffer tank being in communication with the intake system, the outlet of the intake buffer tank being in communication with the inlet of the screw compressor, and the outlet of the screw compressor being in communication with the inlet of the condensation assembly.
[0013] In some embodiments, both the first membrane module and the second membrane module are propylene-preferential permeation type rubber composite membranes. In the working state, the permeate-side outlet outputs permeate gas enriched with propylene, and the retrieval-side outlet outputs retrieval gas enriched with nitrogen.
[0014] In some embodiments, the operating pressure of both the first membrane module and the second membrane module is 0.6-1.2 MPa, and the propylene recovery rate is ≥97%.
[0015] The propylene recovery system of this invention introduces a two-stage propylene-preferential-permeation membrane module based on compression-condensation separation, utilizing the difference in permeation rates between propylene and nitrogen to achieve efficient separation. The system can re-enrich propylene in the uncondensed gas discharged from the separator and return it to the front end of the compression module, forming a closed loop. The propylene recovery rate can reach over 97%. This system is suitable for planned emission treatment during propylene polymerization, propylene separation, and related plant start-up and shutdown periods, with relatively low investment costs and good application value. Attached Figure Description
[0016] Figure 1 This is a schematic diagram of the overall process of the present invention.
[0017] Figure label:
[0018] 1. Air intake system; 11. Propylene polymerization unit; 12. Propylene separation unit; 13. Nitrogen unit; 14. Other propylene units; 15. Process gas unit; 2. Compression component; 3. Condensation assembly; 31. First condenser; 32. Second condenser; 33a. Liquid refrigerant; 33b. Gaseous refrigerant; 4. Separator; 5. First membrane module; 6. Second membrane module; 71. First valve; 72. Second valve; 73. Pressure detection assembly; 74. Control system; 8. Filter assembly; 9. Flare; 10. Nitrogen recovery unit; 11. Propylene recovery unit. Detailed Implementation
[0019] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. 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.
[0020] like Figure 1 As shown, the propylene recovery system of this embodiment includes an inlet system 1, a compression assembly 2, a condensation assembly 3, a separator 4, and a first membrane assembly 5 and a second membrane assembly 6 connected in series. The inlet system 1 is used to introduce a gaseous mixed medium, which includes gaseous propylene and / or nitrogen. The inlet of the compression assembly 2 is connected to the inlet system 1 to increase the pressure of the gaseous mixed medium. The inlet of the condensation assembly 3 is connected to the outlet of the compression assembly 2 to condense the gaseous propylene in the gaseous mixed medium into liquid propylene. The inlet of the separator 4 is connected to the outlet of the condensation assembly 3 to separate the liquid propylene. The first membrane assembly 5 and the second membrane assembly 6 each include an inlet, a retardation-side outlet, and a permeation-side outlet. The inlet of the first membrane assembly 5 is connected to the gas phase outlet of the separator 4, the retardation-side outlet of the first membrane assembly 5 is connected to the inlet of the second membrane assembly 6, the permeation-side outlet of the first membrane assembly 5 is connected to the inlet of the compression assembly 2, the permeation-side outlet of the second membrane assembly 6 is connected to the flare 9 system, and the retardation-side outlet of the second membrane assembly 6 is connected to the nitrogen recovery device 10.
[0021] The propylene recovery system of this embodiment can recover the gaseous mixed medium emitted into the flare 9 system during the start-up and shutdown of the propylene polymerization unit 11, propylene separation unit 12 and related units, reducing propylene waste, and simultaneously recovering nitrogen for reuse. The system as a whole achieves synergistic processing of propylene condensation separation and membrane separation in the gaseous mixed medium. The membrane separation section can further enrich the propylene in the uncondensed gas and return it to the inlet of the compression assembly 2, forming a circular recovery.
[0022] The propylene recovery system provided in this embodiment includes an inlet system 1, a compression assembly 2, a condensation assembly 3, a separator 4, and a first membrane assembly 5 and a second membrane assembly 6 connected in series. The inlet system 1 is used to introduce a gaseous mixture containing gaseous propylene and / or nitrogen. In actual operation, the gaseous mixture mainly comes from gases that are planned to be emitted into the flare 9 system during start-up and shutdown of the propylene polymerization unit 11, the propylene distillation unit, or other propylene-related units; its composition is typically a mixture of propylene and nitrogen.
[0023] The outlet of the intake system 1 is connected to the inlet of the compression assembly 2. The gaseous mixture first enters the compression assembly 2, which increases the pressure of the medium to the level required for subsequent processing. For example, the compression assembly 2 can increase the pressure to approximately 2.0 MPa to meet the operating conditions for condensation and membrane separation. The compressed, high-pressure gaseous mixture enters the inlet of the condensation assembly 3 from the outlet of the compression assembly 2. The condensation assembly 3 is used to condense the gaseous propylene in the gaseous mixture into liquid propylene. The condensation assembly 3 has a refrigerant channel and a process gas channel inside. Through heat exchange between the refrigerant and the gaseous mixture, the latent heat of propylene is removed, thereby realizing the transformation of propylene from the gaseous phase to the liquid phase.
[0024] The outlet of condenser assembly 3 is connected to the inlet of separator 4. After condensation, most of the propylene in the gaseous mixture has been converted into liquid, and the gas-liquid two-phase mixture enters separator 4 together. Separator 4 is used to separate liquid propylene from the gas phase. Liquid propylene accumulates at the bottom of separator 4 and can be led out to propylene recovery unit 11 for recycling, for example, by returning it to the system for reprocessing or by transporting it to a spherical tank for storage. The separated gas phase is discharged from the gas phase outlet of separator 4, and this gas still contains a certain amount of uncondensed propylene and nitrogen.
[0025] The first membrane module 5 and the second membrane module 6 are connected in series. Each of the first membrane module 5 and the second membrane module 6 has an inlet, a reflux-side outlet, and a permeate-side outlet. The inlet of the first membrane module 5 is connected to the gas phase outlet of the separator 4, receiving the gaseous material from the separator 4. The reflux-side outlet of the first membrane module 5 is connected to the inlet of the second membrane module 6, allowing the gas discharged from the reflux side of the first membrane module 5 to directly enter the second membrane module 6 for secondary separation. The permeate-side outlet of the first membrane module 5 is connected to the inlet of the compression assembly 2, sending the propylene-enriched gas from the permeate side back to the front end of the compression assembly 2, where it mixes with the newly entered feed gas and undergoes compression, condensation, and separation again, thereby improving the overall propylene recovery rate. The permeate-side outlet of the second membrane module 6 is connected to the flare 9 system to discharge the permeate gas, which has a low propylene content and can be safely sent to the flare 9 for combustion or venting. The retrieval side outlet of the second membrane module 6 is connected to the nitrogen recovery device 10. Since the permeation rate of nitrogen through the membrane module is much lower than that of propylene, nitrogen is enriched in the gas discharged from the retrieval side outlet and can be returned to the system for continued use as recovered nitrogen.
[0026] During operation, the gaseous mixture flows sequentially through the inlet system 1, the compression assembly 2, the condensation assembly 3, and the separator 4. In the separator 4, the condensed liquid propylene is recovered. The uncondensed gaseous phase enters the first membrane module 5, which uses a membrane material that preferentially allows propylene to permeate. Driven by the pressure difference across the membrane, propylene preferentially permeates through the membrane layer into the permeate side, forming propylene-enriched permeate gas, which returns to the inlet of the compression assembly 2. The gas that does not permeate the membrane (i.e., the retentate side gas) has a relatively lower propylene content but still contains some propylene; this gas enters the second membrane module 6. The second membrane module 6 performs further separation; the propylene content in the gas discharged from its permeate side is now low, and it is sent to the flare system 9. The nitrogen in the gas discharged from its retentate side is significantly enriched and sent to the nitrogen recovery device 10. By connecting these two membrane stages in series and returning the permeate gas from the first membrane module 5 to the compression assembly 2, the system can efficiently recover propylene from the gaseous mixture while simultaneously recovering nitrogen.
[0027] In some embodiments, the condensing assembly 3 includes a first condenser 31 and a second condenser 32 connected in series. Both the first condenser 31 and the second condenser 32 include a refrigerant channel and a process gas channel, wherein the refrigerant channel is used for the flow of refrigerant, the process gas channel is used for the flow of gaseous mixed medium, and the outlet of the process gas channel of the second condenser 32 is connected to the separator 4. The temperature of the refrigerant used in the second condenser 32 is lower than the temperature of the refrigerant used in the first condenser 31.
[0028] In some embodiments, the second condenser 32 further includes a gas phase delivery channel, the inlet end of which is connected to the gas phase outlet of the separator 4, and the outlet end of which is connected to the inlet of the first membrane module 5. The gas phase delivery channel is used to recover the cooling capacity of the gaseous mixed medium flowing inside it.
[0029] This embodiment further defines the structure of the condenser assembly 3. By setting up a two-stage condenser and using a lower refrigerant temperature in the second condenser 32, the gaseous mixed medium can be gradually cooled, improving the liquefaction efficiency of propylene and reducing the propylene content in the uncondensed gas entering the membrane module. Simultaneously, utilizing the gas phase transport channel in the second condenser 32 to recover the cooling capacity of the gas phase outlet gas from the separator 4 helps reduce the refrigerant consumption of the condenser assembly 3 and improves the overall energy efficiency of the system.
[0030] Specifically, the condensing assembly 3 includes a first condenser 31 and a second condenser 32 connected in series. Each of the first condenser 31 and the second condenser 32 has a refrigerant passage and a process gas passage. The refrigerant passage is used for refrigerant flow, and the process gas passage is used for the flow of the gaseous mixed medium. After exiting the outlet of the compression assembly 2, the gaseous mixed medium first enters the process gas passage of the first condenser 31, where it exchanges heat with the refrigerant in the refrigerant passage of the first condenser 31, and a portion of the propylene condenses into a liquid state here. Subsequently, the gas continues to enter the process gas passage of the second condenser 32, where it further exchanges heat with the refrigerant in the refrigerant passage of the second condenser 32. The temperature of the refrigerant used in the second condenser 32 is lower than the temperature of the refrigerant used in the first condenser 31. For example, the first condenser 31 can use circulating water or ambient temperature refrigerant for initial cooling, while the second condenser 32 can use a low-temperature refrigerant, such as a refrigerant at -40°C. The refrigerant enters the second condenser 32 as liquid refrigerant 33a, and after heat exchange, it forms gaseous refrigerant 33b that flows out. This lowers the outlet temperature of the mixed gas to below -20°C, thereby condensing most of the propylene into a liquid state. The outlet of the process gas passage of the second condenser 32 is connected to the separator 4, through which the gas-liquid two-phase mixture enters the separator 4.
[0031] The second condenser 32 is also equipped with a gas phase conveying channel. The inlet end of this gas phase conveying channel is connected to the gas phase outlet of the separator 4, and the outlet end of the gas phase conveying channel is connected to the inlet of the first membrane module 5. After gas-liquid separation is completed inside the separator 4, the discharged gas phase material (i.e., uncondensed gas) flows through this gas phase conveying channel. Since the temperature of this gas phase material is low (e.g., below -20°C), when it flows through the gas phase conveying channel, it can indirectly exchange heat with the gaseous mixed medium in the process gas channel of the second condenser 32 that has not been sufficiently cooled, thereby recovering its cold energy and helping to reduce the temperature of the process gas entering the second condenser 32. After the cold energy is recovered, the gas phase material leaves the outlet end of the gas phase conveying channel and enters the inlet of the first membrane module 5. In this way, the cold energy carried by the low-temperature gas discharged from the separator 4 is effectively utilized, reducing the refrigerant load of the second condenser 32.
[0032] In some embodiments, the propylene recovery system further includes a first pipe, a second pipe, a first valve 71 disposed on the first pipe, and a second valve 72 disposed on the second pipe; one end of the first pipe is connected to the outlet end of the gas phase conveying channel, and the other end is connected to the flare 9 system; one end of the second pipe is connected to the outlet end of the gas phase conveying channel, and the other end is connected to the inlet of the first membrane module 5.
[0033] In some embodiments, the propylene recovery system further includes a pressure detection component 73 and a control system 74; the pressure detection component 73 is located at the gas phase outlet of the separator 4 and is electrically connected to the control system 74, for detecting the pressure at the gas phase outlet of the separator 4 and feeding back the pressure signal to the control system 74; the control system 74 is electrically connected to both the first valve 71 and the second valve 72, and the control system 74 is used to control one of the first valve 71 and the second valve 72 to open and the other to close according to the feedback information from the pressure detection component 73.
[0034] Specifically, one end of the first pipe is connected to the outlet of the gas phase delivery channel, and the other end of the first pipe is connected to the flare 9 system. One end of the second pipe is connected to the outlet of the gas phase delivery channel, and the other end of the second pipe is connected to the inlet of the first membrane module 5. A first valve 71 is installed on the first pipe, and a second valve 72 is installed on the second pipe. By controlling the opening and closing states of the first valve 71 and the second valve 72, the gas flow direction at the outlet of the gas phase delivery channel can be determined: when the first valve 71 is open and the second valve 72 is closed, the gas is directly discharged to the flare 9 system through the first pipe; when the first valve 71 is closed and the second valve 72 is open, the gas enters the first membrane module 5 through the second pipe for subsequent separation.
[0035] In addition, there can typically be one flare 9 in this device, with the first pipe and the second pipe ultimately connected to the same flare 9. Alternatively, a separate flare 9 can be configured for the first pipe and a separate flare 9 for the second pipe, depending on the requirements.
[0036] A pressure detection component 73 is located at the gas phase outlet of separator 4 to detect the gas pressure at that location. The pressure detection component 73 is electrically connected to the control system 74, enabling it to feed back the detected pressure signal to the control system 74 in real time. The control system 74 is electrically connected to both the first valve 71 and the second valve 72. The control system 74 has a preset pressure threshold, determined based on the pressure tolerance range of the first membrane module 5 and the second membrane module 6, as well as the normal operating pressure of the system. When the pressure signal fed back by the pressure detection component 73 is lower than or equal to the preset threshold, the control system 74 determines that the system is operating normally. At this time, it controls the first valve 71 to close and the second valve 72 to open, allowing gas to enter the first membrane module 5 for recovery. When the pressure signal fed back by the pressure detection component 73 is higher than the preset threshold, the control system 74 determines that the gas pressure is too high. To prevent high-pressure gas from directly entering the membrane module and causing damage to the membrane material, it controls the first valve 71 to open and the second valve 72 to close, directly discharging the gas through the first pipeline to the flare 9 system. Once the pressure returns to the normal range, it automatically switches back to the recovery path. Through the above-mentioned automatic switching mechanism, the system can protect the membrane components in a timely manner under abnormal operating conditions, and can resume operation without manual intervention.
[0037] Alternatively, before starting work, the entire system can be purged by introducing only nitrogen into the air intake system 1. After the working pressure reaches the working pressure of the membrane module, gaseous propylene can be slowly introduced, and the second valve 72 can be switched to open for membrane filtration.
[0038] In some embodiments, the propylene recovery system further includes a filter assembly 8, the inlet of which is connected to the air intake system 1, and the outlet of which is connected to the inlet of the compression assembly 2, for filtering solid impurities in the gaseous mixed medium.
[0039] Specifically, the filter assembly 8 has an inlet and an outlet. Its inlet is connected to the intake system 1, and its outlet is connected to the inlet of the compression assembly 2. The gaseous mixture from the intake system 1 first enters the filter assembly 8. Inside the filter assembly 8, solid impurities such as dust, rust, catalyst powder, or pipe debris are trapped on the filter element by the filter medium. The clean gas is then discharged from the outlet of the filter assembly 8 and subsequently enters the inlet of the compression assembly 2. The filter assembly 8 can use a filter with a filtration accuracy of 5 microns or higher. The appropriate filtration accuracy and filtration area are selected based on the actual cleanliness of the gas source. During system operation, differential pressure indicators can be installed before and after the filter assembly 8. When the differential pressure reaches a set value, the operator is prompted to replace or clean the filter element to ensure filtration effectiveness and gas flow capacity.
[0040] In some embodiments, the air intake system 1 includes multiple parallel process pipelines, each process pipeline being equipped with a switch valve, at least some of the process pipelines being used to connect to the nitrogen unit 13 and the process gas unit 15 respectively, and at least some of the process pipelines being used to connect to at least one of the propylene polymerization unit 11, the propylene separation unit 12, and other propylene units 14.
[0041] Specifically, the intake system 1 includes multiple parallel process pipelines. Each process pipeline is equipped with a switch valve for independently controlling the on / off state of the corresponding pipeline. At least some of the process pipelines are used to connect to the nitrogen unit 13 and the process gas unit 15, respectively, whereby the nitrogen unit 13 provides nitrogen and the process gas unit 15 provides a propylene-containing gaseous mixture. At least some of the process pipelines are used to connect to the propylene polymerization unit 11 and / or the propylene separation unit 12, which emit propylene-containing gas into the flare 9 system during start-up and shutdown. By connecting to the intake system 1, the emitted gas can be introduced into the recovery process. The outlets of all process pipelines converge and connect to the inlet of the filter assembly 8 or the compression assembly 2. In actual operation, the corresponding switch valves can be opened according to the stage of the system. For example, during the initial system startup, the valve on the process pipeline connected to nitrogen unit 13 is first opened to introduce nitrogen into the system for airtightness testing and system purging. Once the system pressure stabilizes, the nitrogen pipeline is closed, and the process pipelines connected to process gas unit 15 or propylene polymerization unit 11 and propylene separation unit 12 are gradually opened to introduce a gaseous mixture containing propylene. The arrangement of multiple parallel pipelines allows for independent switching between different gas sources, avoiding mutual interference between gases from different sources, and also facilitates rapid isolation in case of an anomaly in a particular gas source.
[0042] In some embodiments, the compression assembly 2 includes a screw compressor and an intake buffer tank. The inlet of the intake buffer tank is connected to the intake system 1, the outlet of the intake buffer tank is connected to the inlet of the screw compressor, and the outlet of the screw compressor is connected to the inlet of the condenser assembly 3.
[0043] Specifically, the compression assembly 2 includes a screw compressor and an inlet buffer tank. The inlet buffer tank has an inlet and an outlet. Its inlet is connected to the intake system 1, where the gaseous mixture from the intake system 1 first enters the buffer tank. The buffer tank has a certain volumetric space; when the flow rate or pressure of the gaseous mixture fluctuates instantaneously, the buffer tank can absorb or replenish it, significantly reducing the fluctuation amplitude of the outflow. The outlet of the buffer tank is connected to the inlet of the screw compressor. After pressure stabilization, the gaseous mixture flows out of the buffer tank and into the screw compressor. The screw compressor compresses the gaseous mixture, raising its pressure to the level required for subsequent condensation and membrane separation. The outlet of the screw compressor is connected to the inlet of the condensation assembly 3, where the compressed high-pressure gas enters the condensation assembly 3. The screw compressor is suitable for handling compression tasks containing hydrocarbon gases and has a certain tolerance to small amounts of liquid droplets that may be entrained in the intake air. Using it in conjunction with the inlet buffer tank can further improve the system's operational stability.
[0044] In some embodiments, both the first membrane module 5 and the second membrane module 6 are propylene-preferential permeation type rubber composite membranes. In the working state, the permeate side outlet outputs permeate gas enriched with propylene, and the retrieval side outlet outputs retrieval gas enriched with nitrogen.
[0045] In some embodiments, the operating pressure of the first membrane module 5 and the second membrane module 6 is both 0.6-1.2 MPa, and the propylene recovery rate is ≥97%.
[0046] Specifically, both the first membrane module 5 and the second membrane module 6 employ propylene-preferential permeation rubber-state composite membranes. This type of membrane material exhibits a rubber-like state at operating temperatures, resulting in a large free volume. The diffusion rate of propylene molecules within the membrane is significantly higher than that of nitrogen molecules. During operation, a gaseous mixed medium enters the inlet of the membrane module. Driven by the pressure difference across the membrane, propylene preferentially permeates through the membrane layer into the permeate side. Therefore, the gas output from the permeate side outlet is propylene-enriched permeate gas, with a propylene concentration significantly higher than that in the feed gas. Meanwhile, the gas that fails to permeate through the membrane layer exits from the retrieval side outlet, where nitrogen is relatively enriched, forming nitrogen-enriched retrieval gas.
[0047] The operating pressures of both membrane modules 5 and 6 are 0.6 to 1.2 MPa. This pressure range is sufficient to provide the transmembrane pressure differential required for membrane separation without exceeding the mechanical strength limits of the rubber-coated composite membrane. At this operating pressure, combined with the two-stage membrane series configuration and the recirculation design of returning permeate gas to the inlet of compression module 2, the propylene recovery rate of the system can reach over 97%. The propylene recovery rate is defined as the percentage of the total amount of propylene in the feed gas mixture, expressed as the sum of the recovered liquid propylene and the total amount of propylene in the permeate gas returned to compression module 2. A high recovery rate means that very little propylene remains in the gas discharged to the flare 9 system, reducing both feedstock loss and the combustion load on flare 9.
[0048] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0049] 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 technical features indicated. 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.
[0050] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.
[0051] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0052] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. 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.
[0053] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.
Claims
1. A propylene recovery system, characterized in that, include: An intake system for introducing a gaseous mixture, the gaseous mixture comprising gaseous propylene and / or nitrogen; A compression assembly, the inlet of which is connected to the air intake system, is used to increase the pressure of the gaseous mixture. A condensation assembly, the inlet of which is connected to the outlet of the compression assembly, is used to condense gaseous propylene in the gaseous mixed medium into liquid propylene; A separator, the inlet of which is connected to the outlet of the condensation assembly, is used to separate liquid propylene; A first membrane module and a second membrane module are connected in series. Both the first membrane module and the second membrane module include an inlet, a retardation-side outlet, and a permeation-side outlet. The inlet of the first membrane module is connected to the gas phase outlet of the separator, the retardation-side outlet of the first membrane module is connected to the inlet of the second membrane module, the permeation-side outlet of the first membrane module is connected to the inlet of the compression module, the permeation-side outlet of the second membrane module is connected to the flare system, and the retardation-side outlet of the second membrane module is connected to the nitrogen recovery device.
2. The propylene recovery system according to claim 1, characterized in that, The condensation assembly includes a first condenser and a second condenser connected in series. Both the first condenser and the second condenser include a refrigerant passage and a process gas passage, wherein the refrigerant passage is used for the flow of refrigerant, and the process gas passage is used for the flow of the gaseous mixed medium. The outlet of the process gas passage of the second condenser is connected to the separator. The temperature of the refrigerant used in the second condenser is lower than the temperature of the refrigerant used in the first condenser.
3. The propylene recovery system according to claim 2, characterized in that, The second condenser also includes a gas phase delivery channel, the inlet end of which is connected to the gas phase outlet of the separator, and the outlet end of which is connected to the inlet of the first membrane module. The gas phase delivery channel is used to recover the cooling capacity of the gaseous mixed medium flowing inside it.
4. The propylene recovery system according to claim 3, characterized in that, It also includes a first pipe, a second pipe, a first valve installed on the first pipe, and a second valve installed on the second pipe; One end of the first pipeline is connected to the outlet end of the gas phase delivery channel, and the other end is connected to the flare system; One end of the second pipe is connected to the outlet end of the gas phase delivery channel, and the other end is connected to the inlet of the first membrane module.
5. The propylene recovery system according to claim 4, characterized in that, It also includes pressure detection components and control systems; The pressure detection component is located at the gas phase outlet of the separator and is electrically connected to the control system. It is used to detect the pressure at the gas phase outlet of the separator and feed the pressure signal back to the control system. The control system is electrically connected to both the first valve and the second valve. The control system is used to control one of the first valve and the second valve to open and the other to close based on the feedback information from the pressure detection component.
6. The propylene recovery system according to claim 1, characterized in that, It also includes a filter assembly, the inlet of which is connected to the air intake system and the outlet of which is connected to the inlet of the compression assembly, for filtering solid impurities in the gaseous mixture.
7. The propylene recovery system according to claim 1, characterized in that, The air intake system includes multiple parallel process pipelines, each of which is equipped with a switch valve. At least a portion of the process pipelines are used to connect to a nitrogen unit and a process gas unit, respectively, and at least a portion of the process pipelines are used to connect to a propylene polymerization unit and / or a propylene separation unit.
8. The propylene recovery system according to claim 1, characterized in that, The compression assembly includes a screw compressor and an intake buffer tank. The inlet of the intake buffer tank is connected to the intake system, the outlet of the intake buffer tank is connected to the inlet of the screw compressor, and the outlet of the screw compressor is connected to the inlet of the condenser assembly.
9. The propylene recovery system according to claim 1, characterized in that, Both the first membrane module and the second membrane module use propylene-preferential permeation type rubber composite membranes. In the working state, the permeate side outlet outputs permeate gas enriched with propylene, and the retrieval side outlet outputs retrieval gas enriched with nitrogen.
10. The propylene recovery system according to claim 1, characterized in that, The operating pressure of both the first and second membrane modules is 0.6-1.2 MPa, and the propylene recovery rate is ≥97%.