Integrated membrane treatment device and method for oil removal and lithium extraction of ocean platform production water

Abstract

The invention belongs to the technical field of ocean wastewater treatment and resource recovery, and particularly discloses an integrated membrane treatment device and method for oil removal and lithium extraction of ocean platform production water.The device body comprises a first-stage oil removal unit and a second-stage lithium extraction unit which are sequentially connected, the first-stage oil removal unit adopts a hydrophilic modified ultrafiltration membrane or microfiltration membrane, and the second-stage lithium extraction unit adopts a hydrophilic modified ultrafiltration membrane or microfiltration membrane; the oil content of inlet water is reduced to below 10mg / L through cross-flow filtration; the secondary lithium extraction unit adopts a composite adsorption film loaded with a lithium ion sieve, selective lithium extraction is carried out on deoiled water, meanwhile, the device is integrated with a monitoring control system and a cleaning regeneration system, and a modular skid-mounted design is adopted. Through cooperation of two stages of functional membranes, deep oil removal and efficient lithium extraction are synchronously completed in a single compact system, the problems that an adsorption method is poor in oil stain resistance and process equipment is dispersed are solved, and the device has the advantages of being high in anti-pollution capacity, high in resource recovery rate, high in automation degree and suitable for offshore platform space limitation.

Description

Technical Field

[0001] This invention belongs to the field of marine wastewater treatment and resource recycling technology. Specifically, it relates to an integrated membrane treatment device and method for removing oil and extracting lithium from production water on marine platforms. Background Technology

[0002] Offshore platform production water is a major wastewater generated during crude oil extraction, characterized by large volume, high mineralization, and complex composition. Its treatment typically faces a dual objective: first, to meet stringent environmental emission requirements, reducing oil content from hundreds of mg / L to national emission standards (e.g., below 10-20 mg / L); and second, to achieve resource utilization, particularly the recovery of increasingly valuable lithium resources. However, these two objectives are inherently contradictory within the framework of traditional processes. Existing technologies generally employ a segmented treatment model of "oil removal first, lithium extraction later": first, oil is removed using physicochemical methods such as hydrocyclone separation, flotation, coalescence, or media filtration; then, lithium is recovered from the deoiled water using adsorption, extraction, or membrane concentration technologies. This model results in a lengthy process flow, complex equipment, and a large footprint, creating a significant contradiction with the harsh environment of offshore platforms, characterized by limited space, load capacity, and high maintenance costs. More importantly, if the front-end degreasing process fails to completely remove emulsified oil and dissolved organic matter, the residual oil will seriously contaminate, clog, or poison the expensive lithium extraction adsorbents (such as manganese-based and titanium-based ion sieves) in the back-end, causing a sharp decrease in adsorption capacity, difficulty in regeneration, and a surge in operating costs.

[0003] Membrane separation technology is widely used in water treatment due to its advantages such as high efficiency, compactness, and ease of automation. In oil removal, ultrafiltration (UF) and microfiltration (MF) membranes, with their precise sieving action, can efficiently retain emulsified oil droplets and suspended solids, making them effective means of deep oil removal. In lithium extraction, adsorption membranes or functional composite membranes supported with specific ion sieves provide a new approach to achieving efficient lithium ion enrichment by endowing the membrane material with selective adsorption properties. However, the application of existing membrane technologies in this scenario still has limitations: a single oil removal membrane process cannot recover lithium resources; and simply connecting an oil removal membrane and a lithium extraction adsorption membrane in series still faces the aforementioned risks of membrane fouling transfer—oil adhesion, concentration polarization, and pore blockage on the surface of the oil removal membrane reduce its flux and stability, and fluctuations in the quality of its produced water may directly affect the performance and lifespan of the downstream lithium extraction membrane. Currently, there is a lack of an integrated device that can organically couple the functions of the two membrane stages at the system design level and specifically address interface fouling control and coordinated operation. Summary of the Invention

[0004] The purpose of this invention is to overcome the deficiencies in the prior art and provide an integrated membrane treatment device and method for oil removal and lithium extraction from production water on offshore platforms. The aim is to achieve deep oil removal and graded lithium extraction sequentially within a single pressure vessel through the composite and modular design of the membrane, thereby achieving a highly compact device and maximizing lithium recovery.

[0005] The objective of this invention can be achieved through the following technical solutions: This invention provides an integrated membrane treatment device for oil removal and lithium extraction from production water on offshore platforms. The device includes a vertical pressure vessel tank with an outlet at the bottom, an inlet on one side wall, and an oil outlet on the other side wall. The oil outlet is connected to an oil collection bag to collect the oil phase separated from the primary oil removal unit, and the axial height of the oil outlet is slightly lower than that of the inlet. Inside the vertical pressure vessel tank, below the inlet, is a cylindrical skid-mounted unit with an annular interlayer between the skid-mounted unit and the inner wall of the tank serving as an oil phase channel. The skid-mounted unit is connected to the vertical pressure vessel tank via a connector. The inner wall of the skid-mounted unit is connected to the water inlet. A primary oil removal unit and a secondary lithium extraction unit are sequentially arranged inside the skid-mounted unit along the water inlet flow direction. A first liquid distributor and a second liquid distributor are respectively arranged above the primary oil removal unit and the secondary lithium extraction unit, for example, fixed to the inner wall of the skid-mounted unit by flange connection. The side wall of the skid-mounted unit is provided with several uniform small holes in the axial section corresponding to the primary oil removal unit, so that the separated oil phase overflows from the side wall to the oil phase channel and floats to the oil outlet for output. A conical component with a matching upper diameter is connected to the lower part of the skid-mounted unit, for example, fixed to the lower part of the skid-mounted unit by flange connection. The bottom of the conical component is connected to the water outlet.

[0006] In some embodiments of the present invention, the side wall of the vertical pressure vessel tank is provided with an operating hole that communicates with the skid-mounted unit. The operating hole is located in the axial middle section of the skid-mounted unit and has a diameter of 30cm to 60cm. The skid-mounted unit is provided with an openable and closable pressure-bearing sealed door in the area corresponding to the operating hole for replacing the membrane bed in the primary oil removal unit and the secondary lithium extraction unit.

[0007] In some embodiments of the present invention, a first pressure sensor, a second pressure sensor, an online oil analyzer, and a lithium concentration monitor are arranged from top to bottom on the exterior of the vertical pressure vessel tank; the first pressure sensor, the second pressure sensor, the online oil analyzer, and the lithium concentration monitor are all connected to a PLC control unit; the first pressure sensor and the second pressure sensor are respectively located below the first liquid distributor and above the second liquid distributor, and the online oil analyzer and the lithium concentration monitor are located inside the second liquid distributor and below the secondary lithium extraction unit.

[0008] In some embodiments of the present invention, the device further includes a cleaning and regeneration system connected to the PLC control unit, used to automatically trigger water cleaning and acid washing regeneration programs according to a preset differential pressure threshold or lithium ion concentration threshold; specifically, The primary oil removal unit is connected to a backwash water pump for performing a hydraulic backwashing process; furthermore, when hydraulic backwashing is performed, the oil drain port is in a closed state, and the backwash water enters from the outlet and exits from the inlet. The secondary lithium extraction unit is connected to a regenerated liquid supply unit. The regenerated liquid is a hydrochloric acid or sulfuric acid solution with a concentration of 0.1 to 1.5 mol / L, which is used to desorb and regenerate the saturated composite adsorption membrane and collect lithium-rich liquid to recover lithium ions. Furthermore, during desorption and regeneration, the water inlet and oil outlet are closed, and the pickling solution enters from the water outlet. When the pickling solution covers the secondary lithium extraction unit, the water outlet is closed by a valve. After desorption and regeneration for a period of time, the water outlet is opened to discharge the pickling solution.

[0009] In some embodiments of the present invention, the primary oil removal unit is a membrane bed formed by stacking hydrophilic modified ultrafiltration membranes or microfiltration membranes, used to separate oil and water in the production water and reduce the oil content in the production water to below 10 mg / L; the secondary lithium extraction unit is a membrane bed formed by stacking composite adsorption membranes loaded with lithium ion sieves, used to selectively adsorb lithium ions in the production water from the primary oil removal unit.

[0010] In some embodiments of the present invention, the primary oil removal unit adopts a cross-flow filtration mode; the secondary lithium extraction unit adopts a step-by-step filtration adsorption mode; and the hydrophilic modified ultrafiltration membrane or microfiltration membrane is configured as a hollow fiber type, spiral wound type, or plate and frame type. Furthermore, the ultrafiltration membrane is preferably made of polyvinylidene fluoride (PVDF), and the microfiltration membrane is preferably made of polypropylene (PP).

[0011] In some embodiments of the present invention, the composite adsorption membrane loaded with lithium ion sieves is configured as a plate-and-frame type or a roll type; the substrate of the composite adsorption membrane is a porous polymer membrane, a ceramic membrane or a nonwoven fabric, and a manganese-based lithium ion sieve or a titanium-based lithium ion sieve is loaded by physical impregnation, coating or chemical grafting.

[0012] Another aspect of the present invention provides an integrated membrane treatment method for oil removal and lithium extraction from production water on offshore platforms, comprising the following steps: The production water from the offshore platform is introduced into the vertical pressure vessel tank through the inlet and then transported to the primary oil removal unit via the first liquid distributor. The oil phase in the production water is separated in a cross-flow filtration mode to obtain primary purified water with low oil content. The separated oil phase overflows from the side wall of the skid-mounted unit into the oil phase channel and floats to the oil outlet for output, where it is collected by the oil collection bag. At the same time, the separated primary purified water enters the secondary lithium extraction unit through the second liquid distributor to deeply adsorb lithium ions in the water. Finally, the production water that has undergone deep oil removal and meets the lithium content standard flows into the conical component and is discharged from the outlet. Furthermore, the contamination status of the primary oil removal unit is determined based on the preset differential pressure threshold of the cleaning and regeneration system, triggering a water inlet stop and hydraulic backwash cleaning procedure; the adsorption saturation status of the secondary lithium extraction unit is determined based on the preset lithium ion concentration threshold of the cleaning and regeneration system, triggering a water inlet stop and acid washing and regeneration procedure; during this process, when the primary oil removal unit and the secondary lithium extraction unit have been running for a long time, the water inlet can be stopped at any time and the pressure-bearing sealed chamber door can be opened, and a new membrane can be replaced and installed from the operation port for use.

[0013] In some embodiments of the present invention, primary oil removal units with different membrane bed thicknesses are selected for filling based on the oil content of the production water entering the integrated device. Specifically: When the oil content of the production water is 50–200 mg / L, the membrane bed thickness H1 is 20 cm–35 cm. When the oil content of the production water is 200–350 mg / L, the membrane bed thickness H1 is 35 cm–50 cm. When the oil content of the production water is 350-550 mg / L, the membrane bed thickness H1 is 50 cm-85 cm; The membrane bed thickness H2 of the secondary lithium extraction unit is 25cm to 55cm.

[0014] Compared with the prior art, the present invention has the following outstanding advantages: 1. This invention provides an integrated membrane treatment device for oil removal and lithium extraction of oily production water from offshore platforms. It utilizes a primary oil removal unit composed of hydrophilic modified ultrafiltration / microfiltration membranes, connected in series with a secondary lithium extraction unit composed of a composite adsorption membrane loaded with lithium ion sieves. This achieves highly efficient solid-liquid separation and selective adsorption and recovery of lithium ions from oily production water within a single vertical pressure vessel. The device completely isolates the secondary lithium extraction unit from the oil contamination risk of the primary oil removal unit (oil content <10 mg / L), simultaneously solving the problems of oil clogging in adsorption methods and the dispersion of traditional multi-stage process equipment. This significantly improves the stability of lithium resource recovery and the overall device's resistance to oil contamination, offering advantages such as high separation accuracy, good selectivity, and high resource recovery rate.

[0015] 2. The core membrane treatment module of this invention adopts a standardized, quick-pluggable membrane module design. The entire device is integrated into a skid-mounted unit and achieves fully automatic operation, online cleaning and regeneration through an intelligent control system. Its structure is extremely compact and easy to operate and maintain. While ensuring an efficient and complete treatment process, it saves valuable space and labor costs on offshore platforms to the greatest extent. It has outstanding engineering practicality, operational reliability and economic efficiency throughout the entire life cycle. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an integrated membrane treatment unit for removing oil and extracting lithium from production water on offshore platforms.

[0017] Drawing number explanation: 1-Vertical pressure vessel tank, 2-Outlet, 3-Inlet, 4-Oil outlet, 5-Skid-mounted unit, 51-Connector, 6-First-stage oil removal unit, 7-Second-stage lithium extraction unit, 81-First liquid distributor, 82-Second liquid distributor, 91-First pressure sensor, 92-Second pressure sensor, 93-Online oil analyzer, 94-Lithium concentration monitor, 10-PLC control unit, 11-Oil phase channel, 12-Conical component, 13-Operating port. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0019] mechanism: This invention is based on the tiered purification principle of "membrane sieving for oil removal - membrane adsorption for lithium extraction." The first-stage oil removal unit uses a hydrophilically modified ultrafiltration / microfiltration membrane surface and a cross-flow filtration mode to preferentially and efficiently trap oil droplets and mitigate membrane fouling, providing clean production water for the downstream second-stage lithium extraction unit. The second-stage lithium extraction unit utilizes a composite adsorption membrane loaded with lithium ion sieves to deeply enrich lithium ions based on their specific recognition performance. Simultaneously, the device can accurately determine and automatically maintain membrane fouling and adsorption saturation by real-time monitoring of the transmembrane pressure difference and the lithium ion concentration in the produced water.

[0020] Preparation Example 1 The preparation method of composite adsorption membrane loaded with titanium-based lithium ion sieves is relatively conventional in the field. This preparation example includes the following steps: (1) Substrate pretreatment: cut the polyvinyl alcohol nonwoven fabric into the required size, and ultrasonically clean it for 30 min each with acetone, anhydrous ethanol and deionized water respectively. Then dry it in an oven at 60℃ to constant weight to obtain pretreated polyvinyl alcohol nonwoven fabric. (2) Preparation of lithium ion sieve precursor sol: Weigh lithium carbonate and tetrabutyl titanate by molar ratio Li:Ti = 1.05:1; Dissolve lithium carbonate in dilute nitric acid at a ratio of 5-6 mL of 50wt% nitric acid per gram of lithium carbonate, heat to 65℃ and stir until dissolved to obtain a clear lithium salt solution; Mix tetrabutyl titanate and anhydrous ethanol at a volume ratio of 1:3 and stir evenly; Under vigorous stirring, slowly add the lithium salt solution to the ethanol solution of tetrabutyl titanate, continue stirring for 2 hours to form a uniform and transparent light yellow sol, let stand and age for 24 hours to obtain the precursor sol for loading; (3) Impregnation, loading and drying calcination: The pretreated polyvinyl alcohol nonwoven fabric obtained in step (1) is completely immersed in the precursor sol obtained in step (2) and soaked at room temperature for 2 hours. The impregnated nonwoven fabric is taken out and the excess sol on the surface is gently scraped off with a glass rod. It is then placed in a constant temperature drying oven at 40°C and dried for 12 hours to allow the sol to gel and solidify on the fiber surface and in the pores. The dried sample is placed in a muffle furnace and calcined in an air atmosphere. The temperature is increased to 500°C at a rate of 2°C / min and held at this temperature for 2 hours. The sample is then naturally cooled to room temperature to obtain a composite adsorption membrane loaded with a titanium-based lithium ion sieve.

[0021] Example 1 1.1 Integrated membrane treatment device for oil removal and lithium extraction from production water on offshore platforms like Figure 1As shown, the integrated membrane treatment device for oil removal and lithium extraction from production water of offshore platforms in this embodiment includes a vertical pressure vessel tank 1. The vertical pressure vessel tank 1 has an outlet 2 at its bottom, an inlet 3 on one side wall, and an oil outlet 4 on the other side wall. The oil outlet 4 is connected to an oil collection bag (not shown in the figure) to collect the oil phase separated from the primary oil removal unit, and the axial height of the oil outlet 4 is slightly lower than that of the inlet 3. Inside the vertical pressure vessel tank 1, below the inlet 3, is a cylindrical skid-mounted unit 5. An annular interlayer is left between the skid-mounted unit 5 and the inner wall of the vertical pressure vessel tank 1 as an oil phase channel 11. The skid-mounted unit 5 is connected to the inner wall of the vertical pressure vessel tank 1 via a connector 51. A primary oil removal unit 6 and a secondary lithium extraction unit 7 are sequentially arranged inside the skid-mounted unit 5 along the water flow direction. Above the primary oil removal unit 6 and the secondary lithium extraction unit 7 are respectively provided... The first liquid distributor 81 and the second liquid distributor 82 are fixed to the inner wall of the skid-mounted unit 5, for example, by flange connection; the side wall of the skid-mounted unit 5 is provided with several uniform small holes in the axial section corresponding to the first-stage oil removal unit 6, so that the separated oil phase overflows from the side wall to the oil phase channel 11 and floats to the oil outlet for output; a conical component 12 with a matching upper diameter is connected to the lower part of the skid-mounted unit 5, for example, fixed to the lower part of the skid-mounted unit 5 by flange connection, and the bottom of the conical component 12 is connected to the water outlet 2; the side wall of the vertical pressure vessel tank 1 is provided with an operation hole 13 that communicates with the skid-mounted unit 5. The operation hole 13 is located in the axial middle section of the skid-mounted unit 5, and the hole diameter is 30cm to 60cm. The skid-mounted unit 5 is provided with an openable and closable pressure-bearing sealed chamber door (not shown in the figure) in the area corresponding to the operation hole 13, for replacing the membrane bed in the first-stage oil removal unit 6 and the second-stage lithium extraction unit 7; The vertical pressure vessel tank 1 is equipped with a first pressure sensor 91, a second pressure sensor 92, an online oil analyzer 93, and a lithium concentration monitor 94 arranged from top to bottom on its exterior. The first pressure sensor 91, the second pressure sensor 92, the online oil analyzer 93, and the lithium concentration monitor 94 are all connected to the PLC control unit 10. The first pressure sensor 91 and the second pressure sensor 92 are located below the first liquid distributor 81 and above the second liquid distributor 82, respectively. The online oil analyzer 93 and the lithium concentration monitor 94 are located inside the second liquid distributor 82 and below the secondary lithium extraction unit 7. Furthermore, the device also includes a cleaning and regeneration system (not shown in the figure) connected to the PLC control unit 10, used to automatically trigger water cleaning and acid washing regeneration programs according to a preset differential pressure threshold or lithium ion concentration threshold; specifically, The primary oil removal unit 6 is connected to a backwash water pump (not shown in the figure) for performing a hydraulic backwashing procedure; furthermore, when hydraulic backwashing is performed, the oil outlet 4 is in a closed state, and the backwash water enters from the outlet 2 and exits from the inlet 3. The secondary lithium extraction unit 7 is connected to a regenerated liquid supply unit (not shown in the figure). The regenerated liquid is a hydrochloric acid or sulfuric acid solution with a concentration of 0.1 to 1.5 mol / L, which is used to desorb and regenerate the saturated composite adsorption membrane and collect lithium-rich liquid to recover lithium ions. Furthermore, when desorption and regeneration are performed, the water inlet 3 and the oil outlet 4 are closed, and the pickling liquid enters from the water outlet 2. When the pickling liquid covers the secondary lithium extraction unit 7, the water outlet 2 is closed through a valve (not shown in the figure). After desorption and regeneration for a period of time, the water outlet 2 is opened to discharge the pickling liquid.

[0022] Furthermore, the primary oil removal unit 6 is a membrane bed formed by stacking hydrophilic modified ultrafiltration membranes or microfiltration membranes, used to separate oil and water in the production water and reduce the oil content in the production water to below 10 mg / L; the secondary lithium extraction unit 7 is a membrane bed formed by stacking composite adsorption membranes loaded with lithium ion sieves (including but not limited to the composite adsorption membrane obtained by the method of preparation Example 1), used to selectively adsorb lithium ions in the production water from the primary oil removal unit.

[0023] Furthermore, the primary oil removal unit adopts a cross-flow filtration mode; the secondary lithium extraction unit adopts a step-by-step filtration adsorption mode; the hydrophilic modified ultrafiltration membrane or microfiltration membrane has a hollow fiber, spiral wound, or plate and frame structure; the ultrafiltration membrane is preferably made of polyvinylidene fluoride (PVDF), and the microfiltration membrane is preferably made of polypropylene (PP).

[0024] The composite adsorption membrane loaded with lithium ion sieves has a plate-and-frame or roll-up configuration; the substrate of the composite adsorption membrane is a porous polymer membrane, ceramic membrane or nonwoven fabric, and manganese-based lithium ion sieves or titanium-based lithium ion sieves are loaded by physical impregnation, coating or chemical grafting.

[0025] Furthermore, the orifice diameter of the first liquid distributor 81 and the second liquid distributor 82 is 1.5mm to 8mm; preferably, the orifice diameter of the first liquid distributor 81 is 3mm to 8mm and the orifice diameter of the second liquid distributor 82 is 1.5mm to 2.5mm.

[0026] 1.2 Integrated membrane treatment method for oil removal and lithium extraction from production water of offshore platforms Combination Figure 1 The method for oil removal and lithium extraction on offshore platforms using the integrated membrane treatment apparatus described in 1.1 above includes the following steps: The production water from the offshore platform is introduced into the vertical pressure vessel tank 1 through the inlet 3 and then transported to the primary oil removal unit 6 via the first liquid distributor 81. The oil phase in the production water is separated in a cross-flow filtration mode to obtain primary purified water with an oil content of less than 10 mg / L. The separated oil phase overflows from the side wall of the skid-mounted unit 5 into the oil phase channel 11 and floats to the oil outlet 4 for output. It is then collected by the oil collection bag. At the same time, the separated primary purified water enters the secondary lithium extraction unit 7 via the second liquid distributor 82 to deeply adsorb lithium ions in the water. Finally, the production water that has undergone deep oil removal and meets the lithium content standard flows into the conical component 12 and is discharged from the outlet 2. Furthermore, based on the pressure difference threshold preset by the cleaning and regeneration system, the contamination status of the primary oil removal unit 6 is determined, triggering a water inlet stop and hydraulic backwash cleaning procedure; based on the lithium ion concentration threshold preset by the cleaning and regeneration system, the adsorption saturation status of the secondary lithium extraction unit 7 is determined, triggering a water inlet stop and acid washing and regeneration procedure; during this process, when the primary oil removal unit 6 and the secondary lithium extraction unit 7 have been running for a long time, the water inlet can be stopped at any time and the pressure-bearing sealed chamber door can be opened, and a new membrane can be replaced and installed from the operation port 13 for use.

[0027] Furthermore, based on the oil content of the production water entering the integrated unit, primary oil removal units 6 with different membrane bed thicknesses are selected for loading. Specifically: When the oil content of the production water is 50–200 mg / L, the membrane bed thickness H1 is 20 cm–35 cm. When the oil content of the production water is 200–350 mg / L, the membrane bed thickness H1 is 35 cm–50 cm. When the oil content of the production water is 350-550 mg / L, the membrane bed thickness H1 is 50 cm-85 cm; The membrane bed thickness H2 of the secondary lithium extraction unit 7 is 25cm to 55cm.

[0028] Application Example 1 This application example uses the integrated membrane treatment device for oil removal and lithium extraction from production water on offshore platforms as described in Example 1. The vertical pressure vessel tank 1 has a design specification of Φ1200×1500mm (diameter×total height), the cylinder and end cap are made of 316L stainless steel, the design pressure is 0.7MPa, the design temperature is 80℃, the design capacity is 5m³ / h, and the diameter of the skid-mounted unit 5 is 1050 mm.

[0029] The production water of a certain offshore oil and gas field platform has an oil content of 230 mg / L, a suspended solids content of 33.4 mg / L, and a lithium ion concentration of 7.8 mg / L. Based on the oil content in the influent water, the bed thickness H1 is 37 cm and H2 is 35 cm. The primary oil removal unit 6 is a membrane bed formed by stacking hydrophilic modified PVDF ultrafiltration membranes, and its configuration is hollow fiber; wherein, the hydrophilic modified PVDF ultrafiltration membrane is purchased from Jiumu Filtration Technology Co., Ltd., and the model is PVDF010L; The secondary lithium extraction unit 7 is a membrane bed layer formed by stacking composite adsorption membranes loaded with titanium-based lithium ion sieves obtained in Preparation Example 1, and its configuration is a plate and frame type. This application example uses the integrated membrane treatment method for oil removal and lithium extraction from production water of offshore platforms as described in Example 1. During operation, the production water of the offshore platform is introduced from the inlet 3 via an external booster pump at an empty bed flow rate of 2.5 m / h. The water flows uniformly through the primary oil removal unit 6 under the action of the first liquid distributor 81. After treatment by the primary oil removal unit 6, the oil content in the separated aqueous phase is detected by the online oil analyzer 93 and is reduced to below 5 mg / L. Subsequently, the aqueous phase enters the secondary lithium extraction unit 7 for further treatment. Finally, the lithium ion concentration in the production water discharged from the outlet 2 can be maintained below 1 mg / L for a long period of time, and the total lithium recovery rate exceeds 95%.

[0030] Furthermore, the operation and management of the device adopts an intelligent strategy. When the transmembrane pressure difference (the difference monitored by the first pressure sensor 91 and the second pressure sensor 92) rises to 0.3 MPa, the PLC control unit 10 automatically starts the hydraulic backwash cleaning program; when the online lithium ion analyzer 94 detects that the lithium concentration in the effluent rises to the set value of 3 mg / L, it is determined that the adsorption is saturated, and the cleaning and regeneration system pumps in 0.5 mol / L hydrochloric acid solution to circulate and regenerate the adsorption membrane stack for 30 minutes. The desorbed lithium ions enter the acid solution to form a regeneration solution rich in lithium chloride (lithium concentration can reach 2-5 g / L), which is collected and used for subsequent resource recovery.

[0031] Results: After passing through the integrated membrane treatment unit for oil removal and lithium extraction of production water on offshore platforms, the oil content at the effluent was 7.3 mg / L, the suspended solids content was 4.1 mg / L, and the lithium ion concentration was less than 0.4 mg / L, meeting the discharge and reinjection requirements of treated water on offshore platforms.

[0032] Application Example 2 This application embodiment uses the integrated membrane treatment device and method for oil removal and lithium extraction from production water on offshore platforms as described in Application Embodiment 2. However, the membrane materials for the primary oil removal unit 6 and the secondary lithium extraction unit 7 are common commercial membranes that have not undergone specific modifications. The primary oil removal unit 6 uses a commercially available ordinary PVDF ultrafiltration membrane (without hydrophilic modification), with a pore size of 0.1 μm and a pure water flux of approximately 200–300 L / (m²). 2 •h), operating pressure 0.1MPa, configuration is hollow fiber; The secondary lithium extraction unit 7 uses a commercially available ordinary nanofiltration membrane (without lithium-ion loading), with a molecular weight cutoff of approximately 200–500 Da, an operating pressure of 0.5 MPa, and a spiral wound configuration.

[0033] Results: After passing through the integrated membrane treatment unit for oil removal and lithium extraction in offshore platform production water, the oil content of the effluent was 18 mg / L, and the lithium ion concentration was 6.5 mg / L. However, during the experiment, the pressure differential increased rapidly, the backwashing effect was poor, and the membrane was severely fouled, making multiple regenerations impossible and requiring frequent replacement.

[0034] As can be seen from the above data, the integrated device of the present invention can effectively adapt to complex production water quality with higher oil content and lower lithium concentration by adjusting the module thickness, membrane type and operating parameters, and maintain efficient and stable oil removal and lithium extraction performance, fully demonstrating the flexibility, adaptability and wide applicability of the present invention.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present application in any way. Although the present application discloses the preferred embodiment as described above, it is not intended to limit the present application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the technical solution of the present invention are still within the scope of the technical solution.

Claims

1. An integrated membrane treatment device for oil removal and lithium extraction from production water on offshore platforms, characterized in that, The device includes a vertical pressure vessel tank with an outlet at the bottom, an inlet on one side wall, and an oil outlet on the other side wall. Inside the vertical pressure vessel tank, below the inlet, is a cylindrical skid-mounted unit with an annular interlayer between it and the inner wall of the tank serving as an oil phase channel. A conical component with a matching upper diameter is connected below the skid-mounted unit, and its bottom communicates with the outlet. A primary oil removal unit and a secondary lithium extraction unit are sequentially arranged within the skid-mounted unit along the water flow direction. A first liquid distributor and a second liquid distributor are respectively positioned above the primary oil removal unit and the secondary lithium extraction unit.

2. The apparatus according to claim 1, characterized in that, The side wall of the vertical pressure vessel tank is provided with an operating hole that communicates with the skid-mounted unit. The operating hole is located in the axial middle section of the skid-mounted unit and has a diameter of 30cm to 60cm. The skid-mounted unit is provided with an openable and closable pressure-bearing sealed door corresponding to the area of ​​the operating hole.

3. The apparatus according to claim 1, characterized in that, The vertical pressure vessel is equipped with a first pressure sensor, a second pressure sensor, an online oil analyzer, and a lithium concentration monitor from top to bottom on the outside of the tank. The first pressure sensor, the second pressure sensor, the online oil analyzer, and the lithium concentration monitor are all connected to a PLC control unit. The first pressure sensor and the second pressure sensor are located below the first liquid distributor and above the second liquid distributor, respectively. The online oil analyzer and the lithium concentration monitor are located inside the second liquid distributor and below the secondary lithium extraction unit.

4. The apparatus according to claim 3, characterized in that, The device also includes a cleaning and regeneration system connected to the PLC control unit, used to automatically trigger water cleaning and acid washing regeneration programs based on a preset differential pressure threshold or lithium ion concentration threshold; specifically, The primary oil removal unit is connected to a backwash water pump for performing a hydraulic backwashing process. The secondary lithium extraction unit is connected to a regeneration liquid supply unit, which is used to desorb and regenerate the saturated composite adsorption membrane and collect lithium-rich liquid to recover lithium ions.

5. The apparatus according to claim 1, characterized in that, The primary oil removal unit is a membrane bed formed by stacking hydrophilic modified ultrafiltration membranes or microfiltration membranes, used for oil-water separation of production water; The secondary lithium extraction unit is a membrane bed formed by stacking composite adsorption membranes loaded with lithium ion sieves, used to selectively adsorb lithium ions in the permeate from the primary oil removal unit.

6. The apparatus according to claim 5, characterized in that, The hydrophilic modified ultrafiltration membrane or microfiltration membrane has any one of the following configurations: hollow fiber, spiral wound, or plate and frame; the composite adsorption membrane loaded with lithium ion sieve has a plate and frame or spiral wound configuration.

7. The apparatus according to claim 1, characterized in that, The primary oil removal unit adopts a cross-flow filtration mode; the secondary lithium extraction unit adopts a step-by-step filtration and adsorption mode.

8. The apparatus according to claim 1, characterized in that, The orifice diameter of the first liquid distributor and the second liquid distributor is 1.5 mm to 8 mm.

9. An integrated membrane treatment method for oil removal and lithium extraction from production water on offshore platforms, employing the apparatus described in any one of claims 1-8, characterized in that, Includes the following steps: The production water from the offshore platform is introduced into the vertical pressure vessel tank through the inlet and then transported to the primary oil removal unit via the first liquid distributor. The oil phase in the production water is separated in a cross-flow filtration mode to obtain primary purified water with low oil content. Subsequently, the separated oil phase overflows from the side wall of the skid-mounted unit into the oil phase channel and floats to the oil outlet for output. At the same time, the separated primary purified water enters the secondary lithium extraction unit through the second liquid distributor to deeply adsorb lithium ions in the water. Finally, the production water that has undergone deep oil removal and meets the lithium content standard flows into the conical component and is discharged from the outlet.

10. The method according to claim 9, characterized in that, Based on the oil content of the production water entering the integrated unit, the membrane bed thickness of the primary oil removal unit is as follows: When the oil content of the production water is 50–200 mg / L, the membrane bed thickness H1 is 20 cm–35 cm. When the oil content of the production water is 200–350 mg / L, the membrane bed thickness H1 is 35 cm–50 cm. When the oil content of the production water is 350-550 mg / L, the membrane bed thickness H1 is 50 cm-85 cm; The membrane bed thickness H2 of the secondary lithium extraction unit is 25cm to 55cm.

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