A system and process for purifying brine in the salt industry using silicon carbide flat sheet membranes

Abstract

This invention relates to the field of brine purification technology in the salt production industry, and discloses a silicon carbide flat-sheet membrane brine purification system and process for the salt production industry. The invention uses a modular silicon carbide flat-sheet membrane filtration unit as its core, combined with a minimalist pretreatment feeding unit. Through the modular collaborative design of an open-top membrane tank shell at atmospheric pressure, a detachable stackable membrane tower, a negative pressure water production component, an array-type aeration component, and a refined brine backwashing component, it achieves negative pressure suction filtration with the membrane tower completely submerged in the crude brine, directly treating crude brine containing calcium and magnesium precipitates without the need for pre-filtering and circulation equipment. The modular design of each component in this system allows for easy assembly and disassembly, high filtration accuracy, low energy consumption, strong anti-fouling properties, and stable production of calcium and magnesium precipitates. 2+ +Mg 2+ The refined brine with ≤1ppm and SS≤1ppm has significant advantages over traditional ceramic membrane systems in terms of equipment investment, operating costs, membrane life and industrial adaptability. It can be widely used in brine refining in the salt industry and brine refining in chlor-alkali systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of brine purification in the salt making industry, and particularly relates to a silicon carbide flat membrane brine purification system and process in the salt making industry. BACKGROUND

[0002] The core requirement of brine purification in the salt making industry is to efficiently remove calcium and magnesium ions, suspended solids and colloidal impurities in the brine. Membrane separation technology has gradually replaced the traditional chemical sedimentation method and become the mainstream technology path for brine purification. At present, the widely used system in the industry is an alumina and zirconia ceramic membrane filtration system. This system can achieve fine impurity removal through cross-flow filtration, can shorten the sedimentation time in the traditional process, and can improve the quality of the brine. However, it still has the following shortcomings: strict requirements on the water quality of the inlet water, and strong dependence on pretreatment: the existing alumina and zirconia ceramic membranes have poor anti-pollution performance, and must be matched with a complex rough filtration and circulating tank pretreatment system. The brine crude liquid must be subjected to strict pre-treatment, otherwise membrane pollution and scaling will easily occur, resulting in rapid decline of the membrane flux, and even irreversible damage to the membrane assembly. This not only increases the initial equipment investment, but also greatly prolongs the process flow and increases the operation and maintenance complexity; high energy consumption and poor economic efficiency: the existing ceramic membrane system generally uses high-flow cross-flow filtration, which requires a high-power circulating pump to provide driving force. The operation energy consumption is high, the long-term operation cost is high, and it does not meet the green and low-carbon development requirements of the salt making industry; short service life of the membrane assembly and high operation and maintenance cost: the alumina and zirconia ceramic membranes have limited corrosion and pollution resistance, and the service life is only 2-3 years, with high replacement cost of the membrane assembly; at the same time, frequent membrane pollution leads to high frequency of chemical cleaning, usually once every 3-5 days, with large consumption of chemicals, further increasing the later operation and maintenance cost and workload; fixed structure design, poor adaptability and scalability: the structure design of the existing ceramic membrane system is fixed, the membrane assembly installation is complicated, and it cannot be flexibly expanded according to the production capacity requirements of the salt enterprises; and the system structure has poor adaptability to different qualities and different working conditions of the brine in the salt making industry, and it is difficult to meet the individual needs of different sizes and different regions of the salt enterprises.

[0003] The silicon carbide flat membrane has the core advantages of excellent corrosion and heat resistance, high filtration efficiency, strong anti-pollution performance and large packing density due to the excellent properties of high-purity silicon carbide raw materials. It is an ideal technical direction to solve the defects of the existing alumina and zirconia ceramic membrane system. However, at present, there is no customized silicon carbide flat membrane brine purification system for the brine working conditions (high turbidity, strong corrosion and high calcium and magnesium content) in the salt making industry in the industry. It only stays in the basic property research of the silicon carbide membrane material, and does not deeply combine it with the actual working conditions of the salt brine purification. It lacks structure design, function module cooperation and process optimization suitable for the characteristics of the silicon carbide flat membrane, and cannot fully exert its excellent performance. The large-scale application of the silicon carbide flat membrane in the salt making industry is severely limited, and the core technical problems of brine purification in the salt making industry have not been solved. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon carbide flat sheet membrane brine purification system and process for the salt production industry, in order to solve the problems mentioned in the background art. By applying silicon carbide flat sheet membranes to the salt production industry, crude brine containing calcium and magnesium precipitates can be directly treated without strict pre-filtration or circulation equipment. Through process optimization such as negative pressure filtration, synergistic backwashing, and aeration, the system's operating energy consumption is significantly reduced, membrane life is extended, and the system's adaptability to industrialization is improved.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A silicon carbide flat sheet membrane brine purification system for the salt production industry includes a pretreatment feeding unit and a silicon carbide flat sheet membrane filtration unit connected in sequence. Each functional component of the pretreatment feeding unit and the silicon carbide flat sheet membrane filtration unit is a modular structure and can be detachably connected through sealing joints, bolts, and mortise joints.

[0006] The pretreatment feeding unit does not have a pre-filter and sedimentation components. It is only used to convert the raw brine into crude brine containing calcium and magnesium precipitates and then transport the crude brine to the silicon carbide flat sheet membrane filtration unit through the feed pipe. The pretreatment feeding unit can directly use existing two-alkali method, flue gas method or other chemical precipitation methods.

[0007] The silicon carbide flat sheet membrane filtration unit is the core filtration component of the system, including a flat sheet membrane filter, a water production component, and a sludge discharge component. It can also be configured with modular aeration components, backwashing components, chemical cleaning components, and exhaust gas treatment components according to the operating conditions.

[0008] Furthermore, the flat-sheet membrane filter, used for filtering the coarse brine, includes a membrane tank shell, at least one membrane tower, and a feed line; The membrane tank shell is an integrated structure with an open top under normal pressure. A cover plate can be added to the top according to the working conditions. The bottom is integrally formed with an inverted conical thickener with a cone angle of 60~90°. The inner slope is treated with smooth anti-corrosion treatment. There are no dead corners or grooves inside the thickener. A circular sludge discharge port is provided at the bottom of the sludge discharge port. A three-way connector is connected to the bottom of the sludge discharge port for connecting to the sludge discharge component and the chemical cleaning component respectively. The side wall of the membrane tank shell is provided with several sealing interfaces for through-sealing connections of the feed pipeline, aeration component and water production component respectively. The membrane tower is detachably installed on a support base inside the membrane tank shell. A vertical space is left between the bottom of the support base and the top of the thickener to prevent salt mud from clogging the flow holes of the support base. Multiple membrane towers can be installed inside the membrane tank shell as needed, and the membrane towers are arranged in parallel to achieve modular capacity expansion. The membrane tower includes multiple sets of vertically stacked silicon carbide flat sheet membranes. The pore size of each silicon carbide flat sheet membrane is 30~40nm, and the porosity is ≥45%. Furthermore, the membrane tower includes a bottom support base, a multilayer silicon carbide flat membrane assembly, interlayer connectors, and a top water collection cap; The support base is a load-bearing and positioning component of the membrane tower. It is detachably connected to the inner wall below the membrane tank shell. It is hollow in the center and has flow holes in the circumference. The top of the support base is provided with a positioning slot for detachable positioning connection with the sealing frame of the lowest silicon carbide flat membrane module. The silicon carbide flat sheet membrane assembly includes a single silicon carbide flat sheet membrane, a sealing frame, and a flow guiding mesh. The single silicon carbide flat sheet membrane is sealed to the sealing frame to ensure that crude brine cannot seep into the product water side from the edge of the membrane. The flow guiding mesh is sandwiched between two adjacent membrane layers to form a brine flow gap. The flow guiding mesh is detachably connected to the sealing frame for easy cleaning and replacement. The interlayer connector includes positioning guide rods and locking nuts arranged along the four corners of the membrane tower. The four positioning guide rods pass through the positioning holes on the four corners of the sealing frame of each module, and the bottom is detachably connected to the support base. After each membrane module is stacked, it is locked by locking nuts to ensure that the modules are sealed and fit together without deviation. A sealing gasket is installed between the locking nut and the sealing frame to enhance the sealing performance. The top water collection head is detachably connected to the sealing frame of the uppermost membrane module. The top water collection head has an annular water collection cavity inside. The sealing frame has collection grooves on both sides. The collection grooves of each module are aligned vertically to form a vertical water production channel. The outlet of the vertical water production channel of the uppermost membrane is connected to the water collection port inside the top water collection head. The clear liquid from the water production side of each membrane module enters the annular water collection cavity through the vertical water production channel and the water collection port. The upper end of the top water collection head is connected to the water collection head, and the water collection head is connected to the main water production pipe.

[0009] The feed pipeline includes a main feed pipe and several feed branch pipes. The feed pipeline is evenly distributed inside the membrane tank shell. The feed end of the main feed pipe is connected to the pretreatment feed unit through a feed pump and a feed regulating valve. It extends through a sealed interface on the side wall of the membrane tank shell into the interior of the membrane tank shell and is fixed on the inner side wall of the membrane tank shell. The feed regulating valve is electrically connected to a liquid level sensor inside the membrane tank shell to realize automatic liquid level control. The feed branch pipes are arranged at intervals on the main feed pipe and the outlet faces the outside of the membrane tower to ensure that the raw material brine is evenly distributed and surrounds the membrane tower, avoiding direct impact on the membrane tower.

[0010] The water production assembly is used to create negative pressure on the water production side of the flat sheet membrane to drive filtration and deliver refined brine, and includes a main water production pipe, a water collection head, and a negative pressure suction water production pump. Furthermore, the inlet of the permeate main pipe is connected to the permeate side of the flat sheet membrane via the water collection head, and the permeate main pipe is higher than the top of the membrane tower; the permeate pump is installed on the outside downstream of the membrane tank shell and its inlet is connected to the outlet of the permeate main pipe, generating a negative pressure range of (-80~0) kPa. Furthermore, the water production assembly also includes a pressure transmitter installed on the main water production pipe upstream of the water production pump and a flow meter, a turbidity meter, and a water production control valve installed sequentially on the main water production pipe downstream of the water production pump; the pressure transmitter, flow meter, and turbidity meter are all electrically connected to the control system to monitor the water production pressure, flow rate, and water quality in real time, and provide feedback signals to achieve parameter regulation. Furthermore, a product water exhaust branch pipe is connected above the main product water pipe. The product water exhaust branch pipe is located between the product water pump and the flow meter. One end is connected to the main product water pipe through an exhaust check valve, and the other end is connected back to the inside of the membrane tank shell to exhaust air in the pipeline and avoid affecting the filtration efficiency and metering accuracy.

[0011] The sludge discharge assembly is used to discharge the concentrated salt sludge from the thickener, and includes a sludge discharge pipeline. The input end of the sludge discharge pipeline is connected to one end of a tee connector on the sludge discharge port at the bottom of the thickener via a sludge discharge control valve. Furthermore, the sludge discharge assembly also includes a sludge flow meter, a sludge discharge control valve, and / or a sludge pump. The sludge flow meter and the sludge discharge control valve are connected in series on the sludge discharge pipeline. The sludge pump is optional and its input end is connected to the output end of the sludge discharge pipeline. The output end of the sludge pump extends to the sludge treatment system through a pipeline. The sludge can be discharged by suction from the sludge pump or by gravity flow. Furthermore, the salt mud flow meter and mud discharge control valve are both electrically connected to the control system to monitor the mud discharge volume in real time. By adjusting the sedimentation time and mud discharge frequency, the solid content of the discharged mud can be stably controlled at 3%~10%, supporting intermittent or continuous mud discharge, and adapting to raw brine with different impurity contents.

[0012] Preferably, depending on the operating conditions, the silicon carbide flat sheet membrane filtration unit can also be equipped with an aeration component for sweeping the membrane surface and reducing impurity adhesion; the aeration component includes an air compressor, an aeration main pipe, several gas distributors and several aeration distribution pipes. Furthermore, the air compressor is located outside the membrane tank shell, and the output compressed air pressure ranges from 20 to 40 kPa. The air compressor is electrically connected to the control system, and the aeration frequency and aeration intensity can be adjusted according to the membrane fouling situation. Furthermore, the air outlet of the air compressor is sealed and connected to one end of the aeration main pipe, and the aeration main pipe extends into the interior of the membrane tank shell through a sealed interface on the side wall of the membrane tank shell; the number of gas distributors matches the number of membrane towers, the gas distributors are detachably installed at the bottom of the membrane tank shell directly below the support base, and the aeration air distribution pipe is detachably connected to the upper surface of the gas distributor. Furthermore, the aeration cloth air pipe wall is uniformly provided with a number of aeration micropores, and the arrangement density of the aeration cloth air pipe is adapted to the stacking density of the flat membrane module of the membrane tower to ensure that there are no blind spots on the surface of the membrane module; the height of the aeration cloth air pipe is lower than that of the support base. Compressed air enters the gas distributor through the aeration main pipe and then enters the aeration distribution pipe, purging the membrane tower from bottom to top through the flow holes of the support base.

[0013] Preferably, depending on the operating conditions, the silicon carbide flat sheet membrane filtration unit can also be equipped with a backwashing assembly to restore membrane flux; the backwashing assembly includes a backwashing pressure supply component and a backwashing pipeline. Furthermore, the inlet of the backwash pipeline is connected to the downstream section of the turbidity meter of the main water production pipe via a tee connector, and the outlet of the backwash pipeline is connected to the water collection head. Furthermore, the backwash pressure supply component includes a backwash high-level tank or a backwash pump, providing a backwash pressure of 80~150Kpa. The backwash pipeline connected to the input end of the backwash pressure supply component is equipped with a backwash control valve with a check function, used to switch between water production and backwashing conditions. The backwash component and the water production component share the main water production pipe and water collection head, simplifying the connection structure. The backwash water uses refined brine filtered by this system. It is obtained from the main water production pipe through a three-way connector. During backwashing, the refined brine from the backwash pressure supply component enters the water collection head through the backwash pipeline, enters the water production side of the module through the vertical water production pipe, and passes through the membrane layer in the reverse direction to disperse the impurities attached to the raw water side. The aeration component can be turned on during backwashing to improve the backwashing efficiency.

[0014] Preferably, depending on the operating conditions, the silicon carbide flat sheet membrane filtration unit can also be equipped with a chemical cleaning component for deep cleaning of the membrane module and removal of stubborn contaminants; the chemical cleaning component includes an industrial water supply pipeline, a cleaning solution supply pipeline, and a cleaning control valve. Furthermore, the input ends of the industrial water supply pipeline and the cleaning fluid supply pipeline are respectively connected to the industrial water source or the cleaning fluid storage tank, and the output ends are sealed and connected to the main feed pipe through a cleaning control valve and a tee connector; the cleaning discharge pipeline of the chemical cleaning component is connected to the other end of the tee connector of the sludge discharge port of the thickener through a discharge control valve, and the wastewater after cleaning can be discharged to the wastewater treatment system through the cleaning discharge pipeline; the cleaning control valve is electrically connected to the control system, which can realize the automated control of the cleaning process.

[0015] Preferably, depending on the operating conditions, the silicon carbide flat sheet membrane filtration unit can also be equipped with an exhaust gas treatment component, which includes a cover plate and an exhaust gas collection pipe; the cover plate matches the top opening of the membrane tank housing and is detachably connected to the membrane tank housing; the input end of the exhaust gas collection pipe is detachably connected to the cover plate, and the output end is sealed and connected to the input end of the exhaust gas treatment device.

[0016] Another objective of this invention is to provide a purification process using the aforementioned silicon carbide flat-sheet membrane brine purification system. Relying on a membrane tower immersion negative pressure filtration design, it eliminates the need for a pre-filter coarse filtration step, directly treating coarse brine containing calcium and magnesium precipitates. All components work collaboratively, and materials are transported throughout the process via sealed pipelines. Specifically, the process includes the following steps: S1. Feed Preparation: Based on the required number of membrane towers and module layers, the raw brine is fed into the pretreatment feed unit. The calcium and magnesium ions are converted into calcium and magnesium precipitates using the double alkali method or flue gas method. The crude brine containing calcium and magnesium precipitates is pumped by a feed pump or gravity flow according to the site conditions. It is then transported to the membrane tank shell of the flat plate membrane filter through the feed regulating valve and feed pipeline. The feed regulating valve can adjust the liquid level in the membrane tank shell in real time to ensure that the membrane tower is always completely submerged in the crude brine, while ensuring that the water collection head and the product water main are higher than the liquid level. S2. Negative Pressure Membrane Filtration: The negative pressure suction pump of the permeate component is started to form a negative pressure of (-80~0) kPa on the permeate side of the silicon carbide flat sheet membrane module. The negative pressure difference drives the crude brine from the raw water side of the membrane module through the membrane layer into the permeate side. The clear liquid on the permeate side is transported to the permeate main pipe through the collection tanks on both sides of the membrane module, the vertical permeate channel, the annular collection chamber inside the top collection head, and the collection head. After real-time monitoring by the pressure transmitter, flow meter, and turbidity meter, qualified refined brine is obtained and transported to the downstream salt production system. During water production, the air and a small amount of liquid in the permeate main pipe return to the membrane tank shell through the permeate exhaust branch pipe to avoid affecting the filtration efficiency. S3. Concentration and Sludge Discharge: Solid impurities trapped by the membrane module settle into the thickener under gravity. The impurities slide down and accumulate along the smooth conical slope from top to bottom, and are naturally concentrated at the bottom of the thickener to form salt sludge. The salt sludge is discharged into the salt sludge treatment system continuously or intermittently through the sludge discharge port at the bottom of the thickener via the sludge discharge pipeline, by means of a salt sludge pump or gravity flow. S4. Membrane module maintenance: Selectively activate the aeration components according to the crude brine conditions. When the SS content in the crude brine is ≥50ppm or the Ca content is ≥50ppm, activate the aeration components. 2+ +Mg 2+ When the content is ≥80ppm, the aeration components are continuously turned on, and the air compressor output pressure is controlled at 20~40Kpa. Compressed air is delivered to the bottom of the membrane tower through the air compressor, aeration main pipe, gas distributor and aeration air distribution pipe. Microbubbles are formed through the aeration air distribution pipe and pass through the flow holes of the bottom support from bottom to top to sweep the surface of the membrane module from bottom to top, reducing the adhesion of impurities. When the purity of crude brine is high, an intermittent aeration mode is adopted. Periodically close the permeate control valve and permeate pump, open the backwash control valve, and the refined brine is diverted through the permeate main pipe to the backwash pressure supply component. The backwash pressure supply component provides a backwash pressure of 80~150Kpa. The refined brine used for backwashing enters the annular water collection chamber of the top water collection head through the backwash pipeline and water collection head, and is then evenly distributed to the permeate side of each silicon carbide flat sheet membrane module through the vertical permeate channel. It then passes through the membrane layer in the reverse direction to the raw water side, dispersing the impurities trapped on the membrane surface and in the membrane pores, thus achieving backwashing. The dispersed impurities settle into the thickener and are discharged by the sludge discharge component. When the membrane flux drops below 70% of the initial flux, the feed control valve and feed pump are closed, the coarse brine in the membrane tank shell is drained, the chemical cleaning components are started, and the valves of the chemical cleaning pipeline are opened. Industrial water or cleaning solution is transported to the membrane tank shell through the industrial water supply pipeline or cleaning solution supply pipeline and feed pipeline. Industrial water flushing, cleaning solution soaking cleaning, and industrial water re-washing are performed in sequence to clean the membrane tank and membrane tower in an all-round way. The wastewater after cleaning is discharged through the sludge discharge port and cleaning discharge pipeline. During the cleaning solution soaking process, intermittent aeration can be performed to improve the cleaning effect. Beneficial effects

[0017] Due to the adoption of the above technical solution, the technical progress achieved by this invention compared to the prior art is as follows: 1. Fully modular design and standardized sealed connection, with strong adaptability and scalability: All units and functional components of the system are modular structures, and standardized connection methods such as sealing flanges and sealing joints are used between components. They are detachable, replaceable, and optional. The number of membrane tower stacking layers and the number of membrane towers in the membrane tank can be adjusted as needed to realize modular capacity expansion, adapt to salt enterprises of different sizes and brine conditions of different qualities, solve the problems of rigid structure and complicated connection of traditional systems, and greatly improve the convenience of operation and maintenance.

[0018] 2. No need for pre-filtering, significantly simplifying the process: Relying on the high anti-fouling properties of silicon carbide flat sheet membranes and the membrane tower immersion negative pressure filtration design, the pre-treatment equipment such as coarse filters and circulation tanks required by traditional ceramic membrane systems are eliminated. Only a simplified pre-treatment feeding unit is used, which simplifies the process by more than 50%, reduces initial equipment investment by 20% to 30%, and reduces the equipment footprint to 1 / 3 to 1 / 2 of the traditional system.

[0019] 3. Submerged negative pressure filtration significantly reduces operating energy consumption: The membrane tower is completely submerged in coarse brine and uses 0~-80Kpa negative pressure suction to drive filtration, replacing the traditional high-flow cross-flow filtration method. It does not require a high-power circulation pump and reduces energy consumption by more than 30% compared to traditional ceramic membrane systems, meeting the requirements of green and low-carbon development. All components are reliably sealed and connected, ensuring a stable negative pressure environment and stable filtration efficiency.

[0020] 4. Strong antifouling properties, improved membrane life and operational stability: Silicon carbide flat sheet membranes can operate stably in extreme acidic and alkaline environments with pH 1~14, with a service life of 5~8 years, which is 2~3 times that of traditional ceramic membranes; the aeration and backwashing components work together, with a membrane flux recovery rate of ≥95%, extending the chemical cleaning cycle to more than 15 days, reducing reagent consumption by 1 / 3~1 / 2, significantly reducing the probability of membrane fouling, and achieving 0 unplanned shutdowns in 30 days, thus significantly improving operational stability; all components are tightly sealed, with no brine leakage or air leakage, further ensuring stable system operation.

[0021] 5. High filtration accuracy and stable water quality: The silicon carbide flat sheet membrane module has a precisely controlled pore size of 30~40nm and a porosity of ≥45%. It achieves a ≥99.5% rejection rate for calcium and magnesium precipitates and suspended solids, and can stably produce Ca... 2+ +Mg 2+ The refined brine with ≤1ppm and SS≤1ppm meets the raw material requirements of high-end products in the salt industry, and the water production indicators have small fluctuations and strong controllability; the materials are transported in a sealed manner throughout the process to avoid secondary pollution. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the silicon carbide flat sheet membrane filtration unit of the present invention; Figure 2 This is a schematic diagram of the internal structure of the membrane tank shell; Figure 3 This is a schematic diagram of the membrane tower structure; Figure 4 This is a flowchart of the filtering process of the present invention.

[0023] In the diagram: 100-flat sheet membrane filter, 110-membrane tank shell, 120-membrane tower, 121 support base, 122-silicon carbide flat sheet membrane module, 1221-silicon carbide flat sheet membrane, 1222-sealing frame, 1223-flow guide mesh, 123-interlayer connector, 1231-positioning guide rod, 1232-locking nut, 124-top water collection seal, 130-feed pipe, 131-feed main pipe, 132-feed branch pipe, 133-feed pump, 134-feed regulating valve, 140-thickener, 150-sludge discharge port. 200 - Product water assembly, 210 - Product water main pipe, 220 - Water collector, 230 - Product water pump, 240 - Pressure transmitter, 250 - Flow meter, 260 - Turbidity meter, 270 - Product water control valve, 280 - Product water vent branch pipe, 290 - Vent check valve 300 - Sludge discharge assembly, 310 - Sludge discharge pipeline, 320 - Salt sludge flow meter, 330 - Salt sludge pump, 340 - Sludge discharge control valve. 400 - Aeration assembly, 410 - Air compressor, 420 - Aeration main pipe, 430 - Gas distributor, 440 - Aeration distribution pipe 500 - Backwash assembly, 510 - Backwash pump, 520 - Backwash piping, 530 - Backwash control valve 600 - Chemical cleaning components; 610 - Industrial water supply piping; 620 - Cleaning fluid supply piping; 630 - Cleaning control valve; 640 - Cleaning discharge piping. 700 - Exhaust gas treatment component, 710 - Cover plate, 720 - Exhaust gas collection pipe. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments: Example 1:

[0025] like Figures 1-4 As shown, a silicon carbide flat-sheet membrane brine purification system for the salt production industry includes: The pretreatment feeding unit and the silicon carbide flat sheet membrane filtration unit are all modular in structure and can be detachably connected by sealed joints or bolts.

[0026] The pretreatment feed unit does not have a pre-filter or sedimentation assembly and uses the existing two-alkali process device.

[0027] The silicon carbide flat sheet membrane filtration unit includes a flat sheet membrane filter 100, a water production component 200, a sludge discharge component 300, an aeration component 400, a backwashing component 500, a chemical cleaning component 600, and a tail gas treatment component 700.

[0028] The flat sheet membrane filter 100 includes a membrane tank housing 110, a membrane tower 120, and a feed line 130; The membrane tank shell 110 is an integrated structure with an open top under normal pressure. The top is connected to the cover plate 710 by bolts. The bottom is integrally formed with an inverted cone-shaped thickener 140 with a cone angle of 75°. The inner slope is treated with polytetrafluoroethylene for smooth anti-corrosion. The bottom end is provided with a circular sludge discharge port 150. The bottom of the sludge discharge port 150 is connected to the sludge discharge pipe 310 of the sludge discharge component 300 and the cleaning discharge pipe 640 of the chemical cleaning component 600 through a three-way connector. The side wall of the membrane tank shell 110 is provided with five sealing interfaces, which are used for the through-sealing connection of the feed main pipe 131 of the feed pipe 130, the aeration main pipe 420 of the aeration component 400, the water production main pipe 210 and the water production exhaust branch pipe 280 of the water production component 200, and the backwash pipe 520 of the backwash component 500. In this embodiment, four membrane towers 120 are symmetrically installed in pairs on both sides of the permeate main pipe 210. The membrane towers 120 are detachably installed on the support base 121 located inside the membrane tank shell 110. A vertical space is left between the bottom of the support base 121 and the top of the thickener 140. The membrane tower 120 includes 20 vertically stacked silicon carbide flat sheet membranes 122. The pore size of a single silicon carbide flat sheet membrane 1221 is 40 nm, and the porosity is ≥45%. The membrane tower 120 includes a bottom support 121, a 20-layer silicon carbide flat membrane assembly 122, an interlayer connector 123, and a top water collection head 124.

[0029] The support base 121 is detachably connected to the inner wall below the membrane tank housing 110 by bolts. It is hollow in the center and has flow holes in the circumference. The top of the support base 121 is provided with a positioning slot for detachable positioning connection with the sealing frame 1222 of the lowest silicon carbide flat membrane module 122. The silicon carbide flat sheet membrane assembly 122 includes a single silicon carbide flat sheet membrane 1221, a sealing frame 1222, and a flow guiding mesh 1223. The single silicon carbide flat sheet membrane 1221 and the sealing frame 1222 are sealed and connected by a fluororubber sealing ring. A polypropylene flow guiding mesh 1223 is sandwiched between two adjacent membrane layers to form a brine flow gap. The flow guiding mesh 1223 and the sealing frame 1222 are detachably connected for easy cleaning and replacement. The interlayer connector 123 includes stainless steel positioning guide rods 1231 and locking nuts 1232 arranged along the four corners of the membrane tower 120. Each membrane tower 120 uses four positioning guide rods 1231 to pass through the positioning holes on the four corners of the sealing frame 1222 of each module. The bottom of the positioning guide rods 1231 is detachably connected to the support base 121 by threads. After each membrane module is stacked, it is locked by locking nuts 1232. A sealing gasket is installed between the locking nut 1232 and the sealing frame 1222. The top water collection head 124 is detachably connected to the sealing frame 1222 of the uppermost membrane module via a sealing gasket. The top water collection head 124 has an annular water collection cavity inside. Both sides of the sealing frame 1222 are provided with flow collection grooves. The flow collection grooves of each module are aligned vertically to form a vertical water production channel. The outlet of the vertical water production channel of the uppermost membrane is connected to the water collection port inside the top water collection head 124. The clear liquid from the water production side of each membrane module enters the annular water collection cavity through the vertical water production channel and the water collection port. The upper end of the top water collection head 124 is connected to the water collection head 220, and the water collection head 220 is connected to the main water production pipe 210.

[0030] The feed pipeline 130 includes a main feed pipe 131 and six feed branch pipes 132. The feed pipeline 130 is evenly distributed inside the membrane tank housing 110. The feed end of the main feed pipe 131 is connected to the pretreatment feed unit through the feed pump 133 and the feed regulating valve 134. It extends into the membrane tank housing 110 through the sealed interface on the side wall of the membrane tank housing 110 and is fixed on the inner side wall of the membrane tank housing 110. The feed regulating valve 134 is electrically connected to the liquid level sensor inside the membrane tank housing 110. The feed branch pipes 132 are arranged at intervals on the main feed pipe 131 and the outlet faces the outside of the membrane tower 120 to ensure that the raw brine is evenly distributed and surrounds the membrane tower 120, avoiding direct impact on the membrane tower 120.

[0031] The permeate assembly 200 is used to create negative pressure on the permeate side of the flat sheet membrane to drive filtration and deliver refined brine. It includes a permeate main pipe 210, a water collector 220, a negative pressure suction permeate pump 230, a pressure transmitter 240 installed upstream of the permeate pump 230, and a flow meter 250, a turbidity meter 260 and a permeate control valve 270 installed downstream of the permeate pump 230. The inlet of the permeate main pipe 210 is connected to the permeate side of the flat sheet membrane through the water collector 220. The permeate main pipe 210 is higher than the top of the membrane tower 120. The permeate pump 230 is installed on the outside downstream of the membrane tank shell 110 and its inlet is connected to the outlet of the permeate main pipe 210 through a sealing flange. The negative pressure range generated is (-80~0) Kpa. Above the main water supply pipe 210, there is a water supply exhaust branch pipe 280 connected via a tee connector. The water supply exhaust branch pipe 280 is located between the water supply pump 230 and the flow meter 250. One end is connected to the main water supply pipe 210 via an exhaust check valve 290, and the other end is connected back to the inside of the membrane tank shell 110.

[0032] The sludge discharge assembly 300 is used to discharge the salt sludge concentrated by the thickener 140. It includes a sludge discharge pipeline 310, a salt sludge flow meter 320, a salt sludge pump 330, and a sludge discharge control valve 340. The input end of the sludge discharge pipeline 310 is connected to one end of a tee connector on the sludge discharge port 150 at the bottom of the thickener 140 through the sludge discharge control valve 340. The salt mud flow meter 320 and the mud discharge control valve 340 are connected in series on the mud discharge pipeline 310; the input end of the salt mud pump 330 is connected to the output end of the mud discharge pipeline 310, and the output end of the salt mud pump 330 extends to the salt mud treatment system through the pipeline. The salt mud can be discharged by suction from the salt mud pump 330 or by gravity flow. The salt mud flow meter 320 and the mud discharge control valve 340 are electrically connected to the control system to stably control the solid content of the discharged mud to 5% and discharge mud intermittently.

[0033] The aeration assembly 400 is used to sweep the surface of the blown film tower 120 to reduce the adhesion of impurities; the aeration assembly 400 includes an air compressor 410, an aeration main pipe 420, four gas distributors 430 and four sets of aeration distribution pipes 440. Air compressor 410 is a scroll air compressor 410, located outside the membrane tank shell 110, with an output compressed air pressure of 30 kPa. Air compressor 410 is electrically connected to the control system. The air outlet of air compressor 410 is sealed and connected to one end of aeration main pipe 420 through a sealing joint. Aeration main pipe 420 extends into the interior of membrane tank shell 110 through a sealed interface on the side wall of membrane tank shell 110. Gas distributor 430 is detachably installed at the bottom of membrane tank shell 110 directly below support base 121 by stainless steel bolts. Aeration distribution pipe 440 is detachably connected to the upper surface of gas distributor 430 by sealing buckle. The aeration cloth air pipe 440 has uniformly opened aeration micropores with a diameter of 0.5mm on the pipe wall. The arrangement density of the aeration cloth air pipe 440 is adapted to the stacking density of the flat membrane group of the membrane tower 120. The height of the aeration cloth air pipe 440 is lower than that of the support base 121. Compressed air enters the gas distributor 430 through the aeration main pipe 420 and then enters the aeration distribution pipe 440. It then blows the membrane tower 120 from bottom to top through the flow holes of the support base 121.

[0034] The backwash assembly 500 is used to restore membrane flux; the backwash assembly 500 includes a backwash pressure supply component, a backwash pump 510, and a backwash line 520; The inlet of the backwash line 520 is connected to the main product water pipe 210 downstream of the turbidity meter 260 via a tee connector, and the outlet of the backwash line 520 is connected to the water collection head 220. The backwash pump 510 provides a backwash pressure of 120 kPa, and the backwash pipeline 520 connected to the input end of the backwash pump 510 is equipped with a backwash control valve 530 with a check valve function. The chemical cleaning assembly 600 is used for deep cleaning of membrane modules to remove stubborn fouling; the chemical cleaning assembly 600 includes an industrial water supply line 610, a cleaning fluid supply line 620, and a cleaning control valve 630. The input ends of the industrial water supply pipeline 610 and the cleaning fluid supply pipeline 620 are connected to the industrial water source or the cleaning fluid storage tank, respectively, and the output ends are sealed and connected to the feed main pipe 131 through the cleaning control valve 630 and the tee connector. The cleaning discharge pipeline 640 of the chemical cleaning component 600 is connected to the other end of the tee connector of the sludge discharge port 150 of the thickener 140 through the discharge control valve 650. The wastewater after cleaning is discharged to the wastewater treatment system through the cleaning discharge pipeline 640. The cleaning control valve 650 is electrically connected to the control system.

[0035] The exhaust gas treatment assembly 700 includes a cover plate 710 and an exhaust gas collection pipe 720; the cover plate 710 matches the top opening of the membrane tank housing 110, the input end of the exhaust gas collection pipe 720 is detachably connected to the cover plate 710, and the output end is sealed and connected to the exhaust gas treatment device.

[0036] The process flow of this embodiment is as follows: S1. Feed Preparation: Fill four membrane towers 120 and 20-layer modules according to requirements. Send the raw brine into the pretreatment feed unit. Use the double alkali method to convert calcium and magnesium ions into calcium and magnesium precipitates. The crude brine containing calcium and magnesium precipitates is transported to the membrane tank shell 110 of the flat plate membrane filter 100 through the feed pump 133, feed regulating valve 134 and feed pipeline 130. The feed regulating valve 134 regulates the liquid level in the membrane tank shell 110 to ensure that the membrane tower 120 is always completely submerged in the crude brine, while ensuring that the water collection head 220 and the product water main 210 are above the liquid level. S2, Negative Pressure Membrane Filtration: The negative pressure suction pump 230 of the permeate component 200 is started to form a negative pressure of -50 kPa on the permeate side of the silicon carbide flat sheet membrane module 122. The negative pressure difference drives the crude brine from the raw water side of the membrane module through the membrane layer to the permeate side. The clear liquid on the permeate side is transported to the permeate main pipe 210 through the collection tanks on both sides of the membrane module, the vertical permeate channel, the annular collection chamber inside the top collection head 124 and the collection head 220. After real-time monitoring by the pressure transmitter 240, flow meter 250 and turbidity meter 260, qualified refined brine is obtained and transported to the downstream salt production system. During water production, the air and a small amount of liquid in the permeate main pipe 210 return to the membrane tank shell 110 through the permeate exhaust branch pipe 280. The exhaust check valve 290 prevents the liquid in the permeate exhaust branch pipe 280 from flowing back and contaminating the clear liquid on the permeate side. S3, Concentration and Sludge Discharge: Solid impurities trapped by the membrane module settle into the thickener 140 under the action of gravity. The impurities slide down and accumulate along the conical smooth slope from top to bottom, and are naturally concentrated at the bottom of the thickener 140 to form salt mud. The salt mud is discharged intermittently to the salt mud treatment system through the sludge discharge port 150 at the bottom of the thickener 140 and the sludge discharge pipeline 310 via the salt mud pump 330. S4. Membrane module maintenance: Keep the aeration component 400 running continuously. The output pressure of the air compressor 410 is controlled at 20 kPa. Compressed air is delivered to the bottom of the membrane tower 120 through the air compressor 410, the aeration main pipe 420, the gas distributor 430 and the aeration cloth pipe 440. Microbubbles are formed through the aeration cloth pipe 440 and pass through the flow holes of the bottom support 121 from bottom to top, sweeping the surface of the membrane module from bottom to top to reduce the adhesion of impurities. Periodically close the permeate control valve 270 and permeate pump 230, switch the permeate operation to backwash operation, open the backwash control valve 530, and the refined brine is diverted to the backwash pump 510 through the permeate main pipe 210. The backwash pump 510 provides a backwash pressure of 120 kPa. The refined brine used for backwashing enters the annular water collection chamber of the top water collection head 124 through the backwash pipeline 520 and the water collection head 220, and is then evenly distributed to the permeate side of each silicon carbide flat sheet membrane module 122 through the vertical permeate channel. It then passes through the membrane layer in the reverse direction to the raw water side, dispersing the trapped impurities on the membrane surface and in the membrane pores, thus achieving backwashing. The dispersed impurities settle into the thickener 140 and are discharged by the sludge discharge assembly 300. When the membrane flux drops below 70% of the initial flux, the feed control valve 134 and feed pump 133 are closed, the coarse brine in the membrane tank shell 110 is drained, the chemical cleaning component 600 is started, and the cleaning control valve 650 of the chemical cleaning pipeline is opened. Industrial water or cleaning solution is delivered to the membrane tank shell 110 through the industrial water supply pipeline 610 or the cleaning solution supply pipeline 620 and the feed pipeline 130. Industrial water rinsing, cleaning solution soaking cleaning, and industrial water re-rinsing are performed in sequence to clean the membrane tank and membrane tower 120 in all directions. The wastewater after cleaning is discharged through the sludge discharge port 150 and the cleaning discharge pipeline 640. During the cleaning solution soaking process, intermittent aeration can be performed to improve the cleaning effect.

[0037] Comparative Example 1:

[0038] A traditional alumina ceramic membrane filtration system was used, equipped with a coarse filter, a circulation tank and other pretreatment units. A high-flow cross-flow filtration method was adopted. The membrane module was an alumina tubular membrane. Other test conditions were the same as in Example 1.

[0039] The process was carried out according to Example 1, and the entire operation was continuous for 30 days. The results are shown in Table 1.

[0040] It should be noted that, in the description of this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; 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. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0041] The present invention has been described in detail above. However, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, any modifications or improvements that do not depart from the spirit of the present invention are within the scope of protection of the present invention.

Claims

1. A silicon carbide flat-sheet membrane brine purification system for the salt production industry, comprising a pretreatment feeding unit and a silicon carbide flat-sheet membrane filtration unit connected in sequence, wherein each functional component of the pretreatment feeding unit and the silicon carbide flat-sheet membrane filtration unit is a modular structure and detachably connected; the pretreatment feeding unit does not have coarse filtration and sedimentation components, but is only used to convert the raw brine into coarse brine containing calcium and magnesium precipitates and transport the coarse brine to the silicon carbide flat-sheet membrane filtration unit through a feed pipe, characterized in that, The silicon carbide flat sheet membrane filtration unit includes: A flat-plate membrane filter for filtering the coarse brine includes a membrane tank shell, at least one membrane tower, and a feed pipeline. The membrane tank shell is an open-top structure under atmospheric pressure, with an inverted conical thickener integrally formed at the bottom. The membrane tower is detachably installed on a support base inside the membrane tank shell. The membrane tower includes multiple sets of vertically stacked silicon carbide flat-plate membranes, each with a pore size of 30-40 nm and a porosity ≥45%. The feed pipeline includes a main feed pipe and several feed branch pipes. The feed end of the main feed pipe is connected to the pretreatment feed unit via a feed pump and a feed regulating valve. The feed branch pipes are spaced apart on the main feed pipe with their outlets facing outwards from the membrane tower. A permeate assembly for creating negative pressure on the permeate side of a flat sheet membrane includes a permeate main pipe, a collector, and a negative pressure suction permeate pump. The input end of the permeate main pipe is connected to the permeate side of the flat sheet membrane via the collector, and the permeate main pipe is higher than the top of the membrane tower. The permeate pump is installed downstream of the membrane tank shell and its input end is connected to the output end of the permeate main pipe. The negative pressure range of the permeate pump is (-80~0) kPa. A sludge discharge assembly for discharging salt sludge includes a sludge discharge pipeline connected to a sludge discharge port at the bottom of the thickener via a sludge discharge control valve.

2. The silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The membrane tower includes: The bottom support is detachably connected to the inner wall below the membrane tank shell. The support is hollow in the center and has flow holes in the circumference. A multilayer silicon carbide flat sheet membrane assembly, comprising a single silicon carbide flat sheet membrane, a sealing frame, and a flow guiding mesh, wherein the single silicon carbide flat sheet membrane and the sealing frame are sealed together, and the flow guiding mesh is sandwiched between two adjacent modules to form a brine flow gap. Interlayer connectors include positioning guide rods and locking nuts arranged along the four corners of the membrane tower. The positioning guide rods pass through positioning holes on the sealing frame of each module and are detachably locked and sealed to each membrane module by the locking nuts. The top water collection head is detachably connected to the sealing frame of the uppermost membrane module. Both sides of the sealing frame are provided with water collection grooves. The water collection grooves of each module are aligned vertically to form a vertical water production channel. The outlet of the vertical water production channel of the uppermost membrane is connected to the water collection port inside the top water collection head. The water produced by each membrane module enters the annular water collection cavity inside the top water collection head through the water collection port. The upper end of the top water collection head is connected to the water collection head.

3. The silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The water production assembly also includes a pressure transmitter installed on the main water production pipe upstream of the water production pump and a flow meter, a turbidity meter, and a water production control valve installed sequentially on the main water production pipe downstream of the water production pump; a water production exhaust branch pipe is also connected above the main water production pipe, one end of which is connected to the part of the main water production pipe located between the water production pump and the flow meter through an exhaust check valve, and the other end is connected back to the inside of the membrane tank shell.

4. The silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The sludge discharge assembly also includes a sludge flow meter, a sludge discharge control valve, and / or a sludge pump. The sludge flow meter and the sludge discharge control valve are connected in series on the sludge discharge pipeline. The sludge can be discharged by suction from the sludge pump or by gravity flow.

5. A silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The silicon carbide flat sheet membrane filtration unit further includes an aeration assembly, which includes an air compressor, an aeration main pipe, several gas distributors, and several aeration distribution pipes. The air compressor is located outside the membrane tank shell and outputs compressed air with a pressure range of 20~40 kPa. The compressed air enters the gas distributor through the aeration main pipe. The gas distributor is detachably installed at the bottom of the membrane tank shell directly below the support base. The aeration distribution pipes are detachably connected to the upper surface of the gas distributors. Several aeration micropores are evenly distributed on the wall of the aeration distribution pipes, and the height of the aeration distribution pipes is lower than that of the support base.

6. A silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The silicon carbide flat sheet membrane filtration unit further includes a backwashing assembly, which includes a backwashing pressure supply component and a backwashing pipeline; the inlet of the backwashing pipeline is connected to the downstream section of the turbidity meter of the main water production pipe, and the outlet of the backwashing pipeline is connected to the water collection head; the backwashing pressure supply component includes a backwashing high-level tank or a backwashing pump, and the backwashing pipeline connected to the inlet of the backwashing pressure supply component is equipped with a backwashing control valve with a check valve function.

7. A silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The silicon carbide flat sheet membrane filtration unit further includes a chemical cleaning component, which includes an industrial water supply pipeline, a cleaning liquid supply pipeline, and a cleaning control valve. The industrial water supply pipeline and the cleaning liquid supply pipeline are both sealed and connected to the main feed pipe through the cleaning control valve. The cleaning discharge pipeline of the chemical cleaning component is connected to the sludge discharge port of the thickener through the discharge control valve.

8. A silicon carbide flat-sheet membrane brine purification system for the salt-making industry according to claim 1, characterized in that, The silicon carbide flat sheet membrane filtration unit also includes an exhaust gas treatment component, which includes a cover plate and an exhaust gas collection pipe; the cover plate matches the top opening of the membrane tank shell; the input end of the exhaust gas collection pipe is detachably connected to the cover plate, and the output end is sealed and connected to the exhaust gas treatment device.

9. A purification process using the silicon carbide flat-sheet membrane brine purification system according to any one of claims 1-8, characterized in that, Includes the following steps: S1. Feed Preparation: Based on the required number of membrane towers and module layers, the raw brine is fed into the pretreatment feed unit. The calcium and magnesium ions are converted into calcium and magnesium precipitates using the double alkali method or flue gas method. The crude brine containing calcium and magnesium precipitates is pumped by the feed pump or by gravity flow, and transported to the membrane tank shell of the flat plate membrane filter through the feed regulating valve and feed pipeline. The liquid level in the membrane tank shell is adjusted to ensure that the membrane tower is completely submerged in the crude brine, and the water collection head and the main product water pipe are higher than the liquid level. S2, Negative Pressure Membrane Filtration: Start the negative pressure suction pump of the product water component to form a negative pressure of (-80~0) Kpa on the product water side of the silicon carbide flat sheet membrane module, drive the crude brine from the raw water side of the membrane module through the membrane layer into the product water side, and the clear liquid on the product water side is transported to the product water main through the collection tanks on both sides of the membrane module, the vertical product water channel, the annular collection chamber inside the top collection head and the collection head, to obtain qualified refined brine; S3. Concentration and Sludge Discharge: Solid impurities trapped by the membrane module settle under gravity and are concentrated by the thickener to form salt sludge. The salt sludge is discharged continuously or intermittently through the sludge discharge port at the bottom of the thickener via the sludge discharge pipeline, either by suction by the salt sludge pump or by gravity flow. S4. Membrane module maintenance: Selectively activate the aeration components according to the crude brine operating conditions. Compressed air is delivered to the bottom of the membrane tower via the air compressor, aeration main pipe, gas distributor, and aeration air distribution pipe to sweep the membrane module surface from bottom to top. Periodically close the permeate control valve and permeate pump, and open the backwash control valve. The refined brine is diverted to the backwash pressure supply component via the permeate main pipe, and then delivered to the permeate side of the membrane tower via the backwash pipeline and water collection head to achieve backwashing. When the membrane module flux drops below 70% of the initial flux, start the chemical cleaning component. Industrial water or cleaning solution is delivered to the membrane tank shell via the industrial water supply pipeline or cleaning solution supply pipeline and feed pipeline to complete the membrane module cleaning, and then discharged through the sludge discharge port and cleaning discharge pipeline.

10. The purification process according to claim 9, characterized in that, In the backwashing step, the backwashing pressure supply component provides a backwashing pressure of 80~150Kpa. The refined brine used for backwashing enters the annular water collection chamber of the top water collection head through the water collection head, and is then evenly distributed to the water production side of each silicon carbide flat sheet membrane module through the vertical permeate channel. It then passes through the membrane layer in the reverse direction to the raw water side, dispersing the impurities trapped on the membrane surface and within the membrane pores. The dispersed impurities settle into the thickener and are discharged by the sludge discharge component. The aeration component is activated when the SS content in the crude brine is ≥50ppm or the Ca content is ≥50ppm. 2+ +Mg 2+ When the content is ≥80ppm, the aeration components are continuously turned on, and the output pressure of the air compressor is controlled at 20~40Kpa. The compressed air forms tiny bubbles through the aeration distribution pipe and passes through the flow holes of the bottom support from bottom to top, sweeping the surface of the membrane module and reducing the adhesion of impurities. When the purity of the crude brine is high, the intermittent aeration mode is adopted.

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