Nanofiltration treatment process and system for improving utilization efficiency of sodium chloride resource in seawater by-product strong brine

Abstract

The invention discloses a nanofiltration treatment process and system for improving the utilization efficiency of sodium chloride resources in seawater desalination byproduct strong brine, and relates to the technical field of resource utilization of seawater desalination byproduct strong brine. According to the nanofiltration treatment process for improving the utilization efficiency of the sodium chloride resource in the sea light byproduct strong brine, the recovery rate of the nanofiltration device and the dosage of the scale inhibitor are reasonably controlled, the overall recovery rate of a nanofiltration system is improved, and meanwhile stable and efficient operation of the whole process system is guaranteed; and the seawater desalination byproduct strong brine can be more fully and reasonably utilized.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of concentrated brine produced as a by-product of seawater desalination, and in particular to a nanofiltration treatment process for improving resource utilization efficiency of sodium chloride in concentrated brine produced as a by-product of seawater desalination. Background Art

[0002] Currently, the two main desalination technologies used on a large scale in industrialized applications are thermal and membrane methods. The large amounts of fresh water produced by these methods are primarily used for industrial production and drinking, significantly alleviating water shortages in some water-scarce regions and providing essential conditions for their social and economic development. While producing large quantities of fresh water, desalination plants also produce large amounts of sodium chloride-rich brine as a byproduct. This brine is approximately twice as concentrated as ordinary seawater, and direct discharge into the sea can have a certain impact on the local marine environment. Due to its complex composition, the brine produced by desalination is currently primarily used for the production of raw salt in salt pans or discharged directly into the sea. Some coastal soda ash companies also use a small amount of brine directly for salt production, resulting in a low utilization rate.

[0003] Before sodium chloride, a byproduct of seawater desalination, can be used in industrial production, it must be chemically refined to remove impurities such as calcium and magnesium. This consumes large amounts of soda ash and quicklime, produces a large amount of salt mud waste, and is expensive, complex, and labor-intensive. Using nanofiltration technology to refine the brine effectively removes impurities such as calcium, magnesium, and sulfate from the byproduct. This process is simple, eliminates salt mud waste, and significantly reduces the cost of using the refined brine in industrial production. However, due to the inherent limitations of nanofiltration membranes, traditional nanofiltration technology suffers from low recovery rates for refining desalination brine, typically reaching only around 80%. The remaining 20% ​​of brine, due to its low value, must be discharged, resulting in a significant waste of sodium chloride and other calcium and magnesium resources. Existing technologies (such as Publication Nos. CN102515204A and CN117865285A) do not disclose how nanofiltration can improve the utilization efficiency of sodium chloride in desalination brine. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a nanofiltration treatment process for improving the utilization efficiency of sodium chloride resources in desalinated brine, thereby improving the utilization rate of sodium chloride and simultaneously increasing the utilization value of discharged brine, thereby reducing the waste of chemical resources.

[0005] In a first aspect, the present invention provides a nanofiltration treatment process for improving the resource utilization efficiency of sodium chloride in desalinated brine, comprising the following steps: S1. Take the concentrated brine produced by seawater desalination and pre-treat it to remove impurities to produce qualified pre-treated water that meets the water inlet requirements of the nanofiltration equipment; S2, mixing the qualified pre-treated produced water and the second produced water obtained in S4 to form mixed produced water; S3. Adding a scale inhibitor to the mixed produced water, followed by refined filtration through a first nanofiltration device membrane stack to obtain first produced water and first concentrated water. The first produced water is used for resource utilization of sodium chloride; S4. Add scale inhibitor to the first concentrated water, and then refine and filter it through the second nanofiltration equipment membrane stack to obtain second produced water and second concentrated water. After energy recovery, the second concentrated water is recycled or discharged. The second produced water is reused and mixed with the qualified pretreated produced water from S2.

[0006] The above method can reasonably control the recovery rate of the nanofiltration device and the dosage of the scale inhibitor, improve the overall recovery rate of the nanofiltration system, and ensure the stable and efficient operation of the entire process system, so that the concentrated brine by-product of seawater desalination can be more fully and reasonably utilized.

[0007] Furthermore, qualified pre-treated water production indicators: SDI 15 Less than 3, ORP less than 300mv, residual chlorine less than 0.1ppm, iron ion less than 0.05mg / L.

[0008] Furthermore, the addition amount of the S3 scale inhibitor is 2-5 ppm, and the supplementary addition amount of the S4 scale inhibitor is 0-5 ppm; and / or, the liquid after adding the scale inhibitor is pressurized into the first nanofiltration device or the second nanofiltration device.

[0009] Furthermore, the calcium ion content of the first produced water is less than 150 mg / L, the magnesium ion content is less than 300 mg / L, and the sulfate ion content is less than 200 mg / L. And / or the calcium ion content of the second produced water is similar to the calcium ion content of the qualified pretreated produced water.

[0010] Furthermore, in order to solve the problem of decreased filtration efficiency and increased cleaning frequency of the sand filter under the conditions of high temperature in the external natural environment, high temperature of concentrated seawater, and high organic matter content in the biomass, the steps of S1 desalination of the by-product concentrated brine specifically include: S1-1, taking concentrated seawater as a by-product of thermal desalination and concentrated seawater as a by-product of membrane desalination, combining them and introducing them into an inlet buffer tank for mixing to produce mixed concentrated seawater; S1-2. The mixed concentrated seawater is filtered into a sand filter to produce synthetic pretreated product water.

[0011] Furthermore, in S1-1, the volume of concentrated seawater as a by-product of membrane desalination is 0.2 to 4 times the volume of concentrated seawater as a by-product of thermal desalination; and / or, the outlet temperature of the mixed concentrated seawater in the inlet buffer tank is controlled at 25±5°C by adjusting the inlet flow rate ratio of the concentrated seawater as a by-product of thermal desalination and the concentrated seawater as a by-product of membrane desalination; when the external ambient temperature is higher than 30°C, the inlet flow rate ratio of the concentrated seawater as a by-product of thermal desalination and the concentrated seawater as a by-product of membrane desalination is adjusted to control the temperature of the mixed concentrated seawater entering the buffer tank at 23±2°C.

[0012] In the second aspect, the present invention also provides a nanofiltration treatment system for improving the utilization efficiency of sodium chloride resources in desalinated by-product brine, including a pretreatment subsystem, a mixed water production tank, a first nanofiltration device, a concentrated water buffer tank and a second nanofiltration device. The pretreatment subsystem is connected to the mixed water production tank, the mixed water production tank is connected to the first nanofiltration device, the first nanofiltration device and the second nanofiltration device are both provided with a water production pipe and a concentrated water pipe, the concentrated water pipe of the first nanofiltration device is connected to the concentrated water buffer tank, the concentrated water buffer tank is connected to the second nanofiltration device, and the water production pipe of the second nanofiltration device is connected to the mixed water production tank.

[0013] Furthermore, the first nanofiltration device includes a raw water pump, a high-pressure pump, a dosing device and a first nanofiltration device. The two ends of the raw water pump are respectively connected to the mixed water production tank and the high-pressure pump. The dosing device is installed on the connecting pipe between the raw water pump and the high-pressure pump. The high-pressure pump is also connected to the first nanofiltration device; the second nanofiltration device has the same structure as the first nanofiltration device, and its nanofiltration device is named the second nanofiltration device.

[0014] Furthermore, the recovery rate of the first nanofiltration device is controlled at 70% to 80%, the calcium ion removal rate of the first nanofiltration device is controlled at 80% to 92%, the magnesium ion removal rate is controlled at 88% to 98%, the sulfate removal rate is controlled at 96% to 100%, and the sodium chloride retention rate is controlled at 0.2% to 6%; and / or the maximum flux of the first nanofiltration device is 38 L / m 2 .h, stable desalination rate ≥99.2%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600 psi; and / or the flux of the nanofiltration membrane element of the first nanofiltration device is controlled at 6~25 L / m 2 .h, the water inflow of a single membrane element is controlled at 5~10m 3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~4.5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 5%~12%; the overall recovery rate of the first nanofiltration device is controlled at 70%~80%.

[0015] Furthermore, the recovery rate of the second nanofiltration device is controlled at 30% to 80%, the calcium ion removal rate of the second nanofiltration device is controlled at 70% to 90%, the magnesium ion removal rate is controlled at 72% to 95%, the sulfate removal rate is controlled at 92% to 99%, and the sodium chloride retention rate is controlled at -2% to 5%; and / or The maximum flux of the second nanofiltration device is 40L / m 2 .h, stable desalination rate ≥98%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600 psi; and / or The flux of the nanofiltration membrane element of the second nanofiltration device is controlled at 3~30L / m 2 .h, the water inflow of a single membrane element is controlled at 5~15m 3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 2%~12%, and the overall recovery rate of the second nanofiltration device is controlled at 30%~80%.

[0016] The beneficial effects of the present invention are: It can increase the utilization efficiency of sodium chloride resources in desalinated brine from about 75% to about 90%; It can increase the concentration of calcium, magnesium and sulfate ions in nanofiltration concentrated water by about 2 times, making the resource utilization of chemical substances in nanofiltration concentrated water more economically feasible; It can reduce the discharge of concentrated brine by more than 50%, and reduce the impact of concentrated brine discharge on the marine environment; By adding lower temperature membrane desalination by-product concentrated seawater into the thermal desalination by-product concentrated seawater, the temperature of the concentrated seawater entering the sand filter is reduced, thereby increasing the retention of the concentrated seawater in the sand filter filler, improving the sand filter filtering effect, and reducing the turbidity of the produced water. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A flow chart of a nanofiltration treatment process for improving the resource utilization efficiency of sodium chloride in desalinated brine provided by the present invention; Figure 2 A process flow chart of concentrated seawater pretreatment provided by the present invention; Figure 3 A schematic diagram of the structure of a nanofiltration treatment system for improving the resource utilization efficiency of sodium chloride in desalinated brine provided by the present invention; Explanation of reference numbers: 1. Mixed water tank; 11. Raw water pump; 12. High-pressure pump; 2. Safety filter; 3. Energy recovery; 4. Chemical cleaning device; 5. Concentrated water buffer tank; Figure 4This is a flow chart of the nanofiltration treatment process of the comparative example provided by the present invention. DETAILED DESCRIPTION

[0018] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments, but the present invention is not limited thereto.

[0019] In the first aspect, the present invention provides a nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine, such as Figure 1 As shown, the following steps are included: S1. Take the concentrated brine produced as a by-product of the membrane desalination device or the thermal desalination device, remove suspended particles, microorganisms, colloids and other impurities through the pretreatment system, and produce qualified pretreated water that meets the nanofiltration water inlet requirements.

[0020] Furthermore, the SDI of qualified pre-treated water 15 <3, ORP<300mv, residual chlorine<0.1ppm, iron ion<0.05mg / L.

[0021] If necessary, add an appropriate amount of reducing agent. If ORP ≥ 300mv or residual chlorine ≥ 0.1ppm, add sodium bisulfite to make the pretreated water meet the qualified indicators.

[0022] Preferably, the concentrated seawater pretreatment adopts a sand filtration pretreatment method, and the specific steps are as follows: S1-1. Concentrated seawater, a byproduct of thermal desalination, and concentrated seawater, a byproduct of membrane desalination, are drawn through pipelines and mixed in an inlet buffer tank to produce mixed concentrated seawater. The outlet temperature of the mixed concentrated seawater in the inlet buffer tank is within the range of 25±5°C.

[0023] S1-2. The concentrated seawater mixed in the above step S1 is taken into a sand filter for filtration, and qualified pretreated product water is produced under a working pressure of 0.03 MPa.

[0024] like Figure 2 As shown, the sand filtration pretreatment system includes an inlet control valve, an inlet buffer tank, a temperature measurement unit, a water supply pump, an inlet pressure gauge, a sand filter, and an outlet pressure gauge. Specifically, concentrated seawater (BSA) byproducts from thermal desalination and membrane desalination are combined through a pipeline and enter the inlet buffer tank. The flow rates of the two BSAs are controlled by the inlet control valve. After entering the inlet buffer tank, the BSA is mixed to form mixed BSA. The mixed BSA at the outlet of the inlet buffer tank is monitored by the temperature measurement unit and then enters the sand filter through pipelines and a water supply pump. Pressure gauges are installed on the inlet and outlet pipes of the sand filter to monitor the inlet and outlet pressures. After being filtered through the sand filter, the mixed BSA is produced as mixed pretreated product water with a stable turbidity of less than 1 NTU.

[0025] Among them, the working pressure of the sand filter is 0.03MPa, and it is filled from bottom to top: Ф4~8 particle size quartz sand, filling height 280mm; Ф2~4 particle size quartz sand, filling height 100mm; Ф1~2 particle size quartz sand, filling height 100mm; Ф0.5~1 particle size quartz sand, filling height 800mm.

[0026] Example 1 of Sand Filtration Pretreatment of Water Production Take concentrated seawater produced as a byproduct of thermal desalination and concentrated seawater produced as a byproduct of membrane desalination in a volume ratio of 1:1, with a total water volume of 15 cubic meters per hour, and run continuously for 30 days. Every 4 hours, monitor the inlet and outlet pressures through the pressure gauges of the sand filter inlet and outlet pipes. At the same time, sample the mixed pre-treated product water and monitor the turbidity NTU value. When the pressure difference between the inlet and outlet water of the sand filter reaches 0.05MPa or the turbidity of the mixed pre-treated product water reaches 1NTU, it is recorded as an operation cycle, and the sand filter is cleaned by 5 minutes of compressed air purge and 5 minutes of water purge at a flow rate of 25 cubic meters per hour, and then put into operation again. 6 operation cycles were recorded continuously, with an average turbidity of the produced water of 0.12 NTU, a total operation time of 624 hours, and an average operation cycle of 104 hours. The application data is shown in Table 1 below: Table 1 Data of Pretreatment Example 1

[0027] Example 2 of Sand Filtration Pretreatment of Water Production Most aspects are the same as Example 1 of sand filtration pretreatment water production, with the only difference being that the by-product concentrated seawater from thermal desalination and the by-product concentrated seawater from membrane desalination are taken in a volume ratio of 1:6.

[0028] Continuously record 6 operation cycles, the average turbidity of the produced water is 0.11 NTU, the total operation time is 600 hours, and the average operation cycle is 100 hours. The application data is shown in Table 2 below: Table 2 Data of Pretreatment Example 2

[0029] Example 3 of Sand Filtration Pretreatment of Produced Water Most aspects are the same as Example 1 of sand filtration pretreatment water production, with the only difference being that the by-product concentrated seawater from thermal desalination and the by-product concentrated seawater from membrane desalination are taken in a volume ratio of 1:0.5.

[0030] Continuously record 6 operation cycles, the average turbidity of the produced water is 0.04 NTU, the total operation time is 792 hours, and the average operation cycle is 132 hours. The application data is shown in Table 3 below: Table 3 Data of Pretreatment Example 3

[0031] Comparative example of water produced by sand filtration pretreatment Most of the steps are the same as those in Example 1 of sand filtration pretreatment water production, with the only difference being that all concentrated seawater used is concentrated seawater produced as a by-product of thermal seawater desalination.

[0032] Continuously record 6 operation cycles, the average turbidity of the produced water is 0.34 NTU, the total operation time is 312 hours, and the average operation cycle is 52 hours. The application data is shown in Table 4 below: Table 4 Pretreatment comparative data

[0033] S2. Evenly mix the qualified pre-treated produced water and the second produced water in a mixed produced water tank to produce mixed produced water.

[0034] S3. The mixed produced water is transported to the raw water pump inlet of the first nanofiltration device through a pipeline, and then from the raw water pump outlet to the high-pressure pump inlet through a pipeline. The dosing device is connected to the connecting pipeline between the raw water pump and the high-pressure pump, and scale inhibitor is added to the mixed produced water. The produced water with scale inhibitor is pressurized by the high-pressure pump and enters the membrane stack of the first nanofiltration device for refined filtration.

[0035] Preferably, the outlet pressure of the raw water pump of the first nanofiltration device is 0.2-0.5 MPa, and the high-pressure pump of the first nanofiltration device is pressurized to 2.0-3.6 MPa.

[0036] Preferably, the scale inhibitor added to S3 is 2-5 ppm. The water inflow and operating pressure of the first nanofiltration device are controlled by a high-pressure pump with a built-in frequency converter. The scale inhibitor can be a dispersed hydroxyethylidene diphosphonic acid (HEDP) or HYDREX 4102.

[0037] S4. 70% to 80% of the mixed produced water entering the first nanofiltration device is refined and filtered through a membrane stack to remove most of the divalent ions such as calcium, magnesium, and sulfate to produce the first produced water, which is used for subsequent sodium chloride resource utilization; the remaining mixed produced water generates the first concentrated water with a higher content of calcium, magnesium, and sulfate ions than the first produced water, which is then recycled by energy and flows into the concentrated water buffer tank through a pipeline.

[0038] Furthermore, the calcium ion content in the first produced water is less than 150 mg / L, the magnesium ion content is less than 300 mg / L, and the sulfate ion content is less than 200 mg / L.

[0039] S5. The first concentrated water in the concentrated water buffer tank is transported to the raw water pump of the second nanofiltration device through a pipeline, and then transported to the high-pressure pump through the raw water pump. During this transportation process, the dosing device of the second nanofiltration device adds scale inhibitor to the first concentrated water. The first concentrated water with scale inhibitor is pressurized and transported to the membrane stack of the second nanofiltration device for refined filtration through the high-pressure pump.

[0040] Preferably, the outlet pressure of the raw water pump of the second nanofiltration device is 0.2-0.5 MPa, and the outlet pressure of the high-pressure pump of the second nanofiltration device is 2.2-3.6 MPa.

[0041] Furthermore, the amount of scale inhibitor added is 0-5 ppm, and the water inlet and operating pressure of the nanofiltration device 2 are controlled by the frequency conversion device provided by the high-pressure pump.

[0042] S6. 30% to 80% of the first concentrated water with scale inhibitors entering the second nanofiltration device is refined and filtered through a membrane stack to remove most of the divalent ions such as calcium, magnesium, and sulfate, producing a second produced water with a calcium ion content similar to that of the qualified pretreated produced water in S1. The second produced water flows by gravity to the mixed produced water tank for reuse; the remaining first concentrated water with scale inhibitors generates a second concentrated water with a higher content of calcium, magnesium, and sulfate ions than that of the second produced water, which is then recycled for resource utilization or discharged after energy recovery.

[0043] In the above contents recorded in this embodiment, according to 100m 3 The pilot plant with a capacity of 10000 tonnes of brine produced by desalination of seawater per hour was calculated as follows: (1) the utilization efficiency of sodium chloride resources in the brine produced by the desalination of seawater can be increased from about 75% to about 90%. (2) the concentration of calcium, magnesium, and sulfate ions in the nanofiltration brine produced by the system (the brine produced by the second nanofiltration device) can be increased by about 2 times compared with the existing technology, making the resource utilization of chemical substances in the nanofiltration brine more economically feasible; (3) the brine discharge volume of the second nanofiltration device is reduced by more than 50% compared with the original brine production volume, reducing the impact of the brine discharge on the marine environment.

[0044] In a second aspect, the present invention provides a nanofiltration treatment system for improving the utilization efficiency of sodium chloride resources in desalinated brine. Figure 3 As shown, it includes a pretreatment subsystem, a mixed water production tank 1, a first nanofiltration device, a concentrated water buffer tank 5 and a second nanofiltration device, wherein the pretreatment subsystem is connected to the mixed water production tank 1, the mixed water production tank 1 is connected to the first nanofiltration device through a pipeline, the first nanofiltration device is provided with a produced water outlet and a concentrated water outlet, and its concentrated water outlet is connected to the concentrated water buffer tank 5, and the concentrated water buffer tank 5 is connected to the second nanofiltration device, and the second nanofiltration device is also provided with a produced water outlet and a concentrated water outlet, and its produced water outlet is connected to the mixed water production tank.

[0045] The pretreatment subsystem is the aforementioned sand filtration pretreatment system; An electromagnetic flowmeter is installed on the connecting pipe between the pretreatment subsystem and the mixed water production tank 1. A paddle stirrer is installed in the mixed water production tank. The qualified pretreated water and the second water are fully stirred and mixed by the paddle stirrer to form mixed water.

[0046] The first nanofiltration device has the same structure as the second nanofiltration device, and the structure is described by taking the first nanofiltration device as an example.

[0047] The first nanofiltration equipment includes a raw water pump 11, a high-pressure pump 12, a pressurizing device and a first nanofiltration device. The raw water pump 11 and the high-pressure pump 12 are connected by a pipeline. A dosing device is installed on the connecting pipeline between the raw water pump 11 and the high-pressure pump 12, and the high-pressure pump is connected to the first nanofiltration device through a pipeline.

[0048] Preferably, the raw water pump 11 uses a centrifugal pump with a flow component made of 2205 duplex steel and a head of 50m. A safety filter 2 is installed on the outlet pipe of the raw water pump 11. The dosing device consists of a dosing box and a metering pump. The metering pump is installed at the outlet of the dosing box. The dosing box is equipped with a liquid level gauge for verifying the dosage. The high-pressure pump 12 uses a centrifugal pump with a flow component made of 2507 super duplex steel, frequency conversion control, a head of 400m, and the outlet pipe is connected to the main inlet pipe of the membrane stack of the first nanofiltration device. The high-pressure pump frequency conversion is used to control the water inlet of the system. A pneumatic regulating valve is installed in front of the energy recovery device on the concentrated water pipeline to adjust the recovery rate of the nanofiltration device. Preferably, the outlet pressure of the raw water pump of the first nanofiltration device is 0.2~0.5MPa, and the outlet pressure of the high-pressure pump of the first nanofiltration device is 2.0~3.6MPa.

[0049] Two swing heads are set on the pipeline from the high-pressure pump 12 to the membrane stack. One of them is connected to the outlet of the flushing pump. The water inlet of the flushing pump adopts the first produced water, and the membrane stack is flushed regularly to reduce the risk of scaling; the other is connected to the chemical cleaning device 4. The chemical cleaning device is a conventional equipment that can be purchased. It consists of a chemical washing pump, a chemical washing tank and a safety filter. It uses non-oxidizing fungicides, hydrochloric acid, caustic soda, etc. as cleaning agents, and chemically cleans the membrane stack according to the operating parameters of the membrane stack.

[0050] The first nanofiltration device uses nanofiltration membrane elements with a higher desalination rate. The calcium ion removal rate is controlled at 80%~92%, the magnesium ion removal rate is controlled at 88%~98%, the sulfate removal rate is controlled at 96%~100%, and the sodium chloride retention rate is controlled at 0.2%~6%.

[0051] Furthermore, the first nanofiltration device membrane stack uses 8040 specification nanofiltration membrane elements, 7 cores, and the effective membrane area of ​​a single nanofiltration membrane element is 37.2m 2 , maximum flux 38L / m 2 .h, stable desalination rate ≥99.2%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600psi. Or the flux of the nanofiltration membrane element of the first nanofiltration device is controlled at 6~25L / m 2 .h, the water inflow of a single membrane element is controlled at 5~10m 3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~4.5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 5%~12%; the overall recovery rate of the first nanofiltration device is controlled at 70%~80%.

[0052] The mixed produced water is filtered through the membrane stack to produce the first produced water. The calcium ion content of the first produced water is less than 150 mg / L, the magnesium ion content is less than 300 mg / L, and the sulfate ion content is less than 200 mg / L. It is sent to the next process through the produced water pump and produced water pipeline of the first nanofiltration device to be used as raw material for resource utilization of sodium chloride. The remaining mixed produced water is the first concentrated water. After energy recovery 3, it flows to the concentrated water buffer tank through the concentrated water pipeline of the first nanofiltration device. Electromagnetic flowmeters are respectively installed in the produced water pipeline and the concentrated water pipeline.

[0053] The first nanofiltration unit's concentrate pipeline is equipped with two separate spinners. One of these spinners is connected to the mixed water tank via a pipeline for discharging flushing water there, while the other is connected to chemical cleaning tank I via a pipeline for circulating chemical cleaning. The first nanofiltration unit's concentrate pipeline is equipped with another spinner, which is connected to chemical cleaning tank I via a pipeline for circulating chemical cleaning.

[0054] The first concentrated water passes through the raw water pump and dosing device of the second nanofiltration device, and then adds 0~5ppm of scale inhibitor to the first concentrated water. It then enters the high-pressure pump of the second nanofiltration device after being pressurized by the high-pressure pump of the second nanofiltration device and enters the membrane stack of the second nanofiltration device for filtration. Preferably, the outlet pressure of the raw water pump of the second nanofiltration device is 0.2~0.5MPa, and the outlet pressure of the high-pressure pump of the second nanofiltration device is 2.2~3.6MPa. The first concentrated water is filtered through the membrane stack to produce the second produced water, which is sent to the mixed produced water tank through the produced water pipeline of the second nanofiltration device. The remaining first concentrated water is the second concentrated water. After energy recovery, it flows through the concentrated water pump and concentrated water pipeline of the second nanofiltration device to the next process for resource utilization or discharge. The produced water pipeline and concentrated water pipeline of the second nanofiltration device are respectively provided with electromagnetic flowmeters.

[0055] The difference from the first nanofiltration device is that the second nanofiltration device uses nanofiltration membrane elements with a lower desalination rate, with the calcium ion removal rate controlled at 70%~90%, the magnesium ion removal rate controlled at 72%~95%, the sulfate removal rate controlled at 92%~99%, and the sodium chloride retention rate controlled at -2%~5%.

[0056] Preferably, the second nanofiltration device membrane stack uses 8040 specification nanofiltration membrane elements, 7 cores, and the effective membrane area of ​​a single nanofiltration membrane element is 37.2m 2 , maximum flux 40L / m 2 .h, stable desalination rate ≥98%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600psi; alternatively, the flux of the nanofiltration membrane element of the second nanofiltration device is controlled at 3~30L / m 2 .h, the water inflow of a single membrane element is controlled at 5~15m3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 2%~12%, and the overall recovery rate of the second nanofiltration device is controlled at 30%~80%.

[0057] The brine pipeline of the second nanofiltration unit is equipped with two additional spinners. One of the spinners is connected to the brine buffer tank via a pipe to discharge flushing water to the brine buffer tank, and the other is connected to the chemical washing tank II via a pipe for circulating chemical washing. The water production pipeline of the second nanofiltration unit is also equipped with a spinner that is connected to the chemical washing tank II via a pipe for circulating chemical washing.

[0058] The first nanofiltration device and the second nanofiltration device are both equipped with a concentrate regulating valve, which controls the concentrate flow rate and the produced water flow rate to adjust the produced water recovery rate of the corresponding device.

[0059] Example 1 of the overall process: Based on Example 2 of sand filtration pretreatment of water production, actual production operation was carried out according to the above system and process method. The production indicators were operated for 30 days as a cycle. The average values ​​within one cycle are shown in Table 5 below: Table 5

[0060] The desalinated brine is pumped to the pretreatment system to produce 98m 3 / h, SDI 15 Qualified pretreated product water with an ORP of 2.2, ORP of 215mv, residual chlorine of 0.03ppm, and iron ion of 0.02mg / L was mixed evenly with the second product water in the mixed product water tank and then pumped to the first nanofiltration device. The dosing device added scale inhibitor at 3ppm, adjusted the frequency conversion of the high-pressure pump of the first nanofiltration device and the pneumatic regulating valve on the brine pipeline to control the outlet pressure of the high-pressure pump of the first nanofiltration device to 2.5MPa, with a recovery rate of 76.42%. The generated first product water was pumped to the next process for sodium chloride resource utilization, and the first brine flowed into the brine buffer tank by gravity after energy recovery. The first concentrated water in the concentrated water buffer tank is pumped to the second nanofiltration equipment, and the scale inhibitor is added at 2ppm using the dosing device of the second nanofiltration equipment. The high-pressure pump frequency conversion of the second nanofiltration equipment and the pneumatic regulating valve on the concentrated water pipeline are adjusted to control the high-pressure pump outlet pressure of the second nanofiltration equipment to 2.7MPa, with a recovery rate of 69.81%. The generated second produced water flows through the pipeline to the mixed water tank. After energy recovery, the second concentrated water is pumped to the next process for resource utilization or discharge.

[0061] From the time the system was put into operation according to the above parameters, calcium, magnesium, sulfate, and sodium ion indicators of the pretreated product water, primary product water, primary concentrate, secondary product water, and secondary concentrate were sampled and analyzed every four hours. Electromagnetic flowmeters were used to record the flow rates of the various media in the pretreated product water pipeline, the product water pipeline and concentrate pipeline of the first nanofiltration device, and the product water pipeline and concentrate pipeline of the second nanofiltration device. A 30-day operation cycle was defined as one cycle, and the operating indicators are shown in Table 1 above. During this 30-day cycle, the nanofiltration treatment system achieved a recovery rate of 91.48%, and a sodium chloride utilization rate of 88.8%.

[0062] Example 2 of the overall process The production indicators are run for 30 days as a cycle. The average values ​​within a cycle are shown in Table 6 below: Table 6

[0063] The concentrated brine from seawater desalination is pumped to the pretreatment system to produce 99.9m 3 / h, SDI 15 Qualified pretreated product water was 2.1, ORP 208mv, residual chlorine 0.02ppm, and iron ion 0.03mg / L. The dosing device of the first nanofiltration unit added scale inhibitor at a rate of 3ppm, and the outlet pressure of the high-pressure pump of the first nanofiltration unit was controlled at 2.4MPa. The recovery rate was 75.02%. The resulting primary product water was pumped to the next process for sodium chloride resource utilization. After energy recovery, the primary concentrate flowed into the concentrate buffer tank by gravity. The primary concentrate in the concentrate buffer tank was pumped to the second nanofiltration unit. The dosing device of the second nanofiltration unit added scale inhibitor at a rate of 2ppm. The outlet pressure of the high-pressure pump of the second nanofiltration unit was controlled at 2.9MPa. The recovery rate was 67%. The secondary product water flowed through a pipeline to the mixed product tank by gravity. After energy recovery, the secondary concentrate was pumped to the next process for resource utilization or discharged.

[0064] From the time the device was put into operation according to the above parameters, calcium, magnesium, sulfate, and sodium ion indicators of the pretreated product water, primary product water, primary concentrate, secondary product water, and secondary concentrate were sampled and analyzed every four hours. Electromagnetic flowmeters were used to record the flow rates of the various media in the pretreated product water pipeline, the product water pipeline and concentrate pipeline of the first nanofiltration device, and the product water pipeline and concentrate pipeline of the second nanofiltration device. A 30-day operation cycle was defined as one cycle. The operating indicators are shown in Table 2 above. Within this 30-day cycle, the nanofiltration system recovery rate reached 90.1%, and the sodium chloride utilization rate reached 88.62%.

[0065] Example 3 of the overall process The production indicators are operated for 30 days as a cycle. The average values ​​within a cycle are shown in Table 7 below: Table 7

[0066] The desalinated brine is pumped to the pretreatment system to produce 100.5m 3 / h, SDI 15 Qualified pretreated permeate (1.9, ORP 211mv, residual chlorine 0.03ppm, and iron ion 0.03mg / L) was mixed evenly with the secondary permeate in a mixing tank and then pumped to the first nanofiltration unit. A scale inhibitor was added at a rate of 3ppm by a dosing device, and the outlet pressure of the high-pressure pump of the first nanofiltration unit was controlled at 2.6MPa. The recovery rate was 76.71%. The primary permeate was pumped to the next process for sodium chloride resource utilization. The secondary brine, after energy recovery, flowed by gravity into the brine buffer tank. The primary brine in the brine buffer tank was pumped to the second nanofiltration unit. The dosing device of the second nanofiltration unit added additional scale inhibitor at a rate of 2ppm, and the outlet pressure of the high-pressure pump of the second nanofiltration unit was controlled at 2.8MPa. The recovery rate was 69.94%. The secondary permeate flowed by gravity to the mixing tank. After energy recovery, the secondary brine was pumped to the next process for resource utilization or discharged.

[0067] From the time the device was put into operation according to the above parameters, calcium, magnesium, sulfate, and sodium ion indicators of the pretreated product water, primary product water, primary concentrate, secondary product water, and secondary concentrate were sampled and analyzed every four hours. Electromagnetic flowmeters were used to record the flow rates of the various media in the pretreated product water pipeline, the product water pipeline and concentrate pipeline of the first nanofiltration device, and the product water pipeline and concentrate pipeline of the second nanofiltration device. A 30-day operation cycle was defined as one cycle. The operating indicators are shown in Table 3 above. Within this 30-day cycle, the nanofiltration system recovery rate reached 91.63%, and the sodium chloride utilization rate reached 89.89%.

[0068] Example 4 of the overall process Based on Example 3 of sand filtration pretreatment of water production, actual production operation was carried out according to the above system and process method. The production indicators were operated for 30 days as a cycle. The average values ​​within one cycle are shown in Table 8 below: Table 8

[0069] The desalinated brine is pumped to the pretreatment system to produce 100.05m 3 / h, SDI 15Qualified pretreated product water was 2.2, with an ORP of 218mv, residual chlorine of 0.03ppm, and iron ion of 0.03mg / L. The dosing device of the first nanofiltration unit added a scale inhibitor at a rate of 3ppm, and the outlet pressure of the high-pressure pump of the first nanofiltration unit was controlled at 2.2MPa. The recovery rate was 78.55%. The resulting primary product water was pumped to the next process for sodium chloride resource utilization. The primary concentrate was then energy recovered and flowed into the concentrate buffer tank by gravity. The primary concentrate in the concentrate buffer tank was pumped to the second nanofiltration unit. The dosing device of the second nanofiltration unit added a scale inhibitor at a rate of 2ppm. The outlet pressure of the high-pressure pump of the second nanofiltration unit was controlled at 2.7MPa. The recovery rate was 67.94%. The secondary product water flowed by gravity through a pipeline to the mixed product tank. After energy recovery, the secondary concentrate was pumped to the next process for resource utilization or discharged.

[0070] From the time the device was put into operation according to the above parameters, the calcium, magnesium, sulfate, and sodium ion indicators of the pre-treated water, the first produced water, the first concentrated water, the second produced water, and the second concentrated water were sampled and analyzed every 4 hours, and the flow rate of each medium was recorded using the electromagnetic flowmeters on the pre-treated water delivery pipeline, the water production pipeline and concentrated water pipeline of the first nanofiltration device, and the water production pipeline and concentrated water pipeline of the second nanofiltration device. 30 days was recorded as an operation cycle, and the operation indicators are shown in Table 2 above. Within the 30-day cycle, the recovery rate of the nanofiltration system reached 91.95%, and the utilization rate of sodium chloride reached 91.04%. Comparative example of the overall process according to Figure 4 The process flow shown is used for production operation. The production indicators are operated for 30 days as a cycle. The average values ​​within a cycle are shown in Table 9 below: Table 9

[0071] The concentrated brine from seawater desalination is pumped to the pretreatment system to produce 99m 3 / h, SDI 15 Qualified pretreated produced water with an ORP of 2.1, 213mv, 0.02ppm residual chlorine, and 0.02mg / L iron ion was pumped to the first nanofiltration equipment. The dosing device added scale inhibitor at 3ppm. The outlet pressure of the high-pressure pump of the first nanofiltration equipment was controlled at 2.3MPa. The recovery rate was 76.3%. The first produced water was pumped to the next process for sodium chloride resource utilization, and the first concentrated water was discharged after energy recovery.

[0072] From the time the system was put into operation according to the above parameters, calcium, magnesium, sulfate, and sodium ion indicators in the pretreated product water, the first product water, and the first concentrate water were sampled and analyzed every four hours. Electromagnetic flowmeters in the pretreated product water pipeline, the product water pipeline of the first nanofiltration device, and the concentrate water pipeline were used to record the flow rates of each medium. A 30-day operation cycle was defined as one cycle. The operating indicators are shown in Table 4 above. During this 30-day cycle, the nanofiltration system recovery rate was 76.3%, and the sodium chloride utilization rate was 73.73%.

[0073] Comparison of the data between the examples and comparative examples shows that the process and system provided by the present invention achieve the purpose of improving the utilization efficiency of sodium chloride resources in the desalinated by-product brine, while reducing the discharge of brine, increasing the concentrations of calcium, magnesium, and sulfate ions in the nanofiltration brine, and making the resource utilization of chemical substances in the nanofiltration brine more economically feasible.

[0074] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art may make changes and modifications to the present invention. If these modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered to be within the scope of protection of the present invention.

Claims

1. A nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine, characterized in that: The steps include: S1. Take the concentrated brine produced by seawater desalination and pre-treat it to remove impurities to produce qualified pre-treated water that meets the water inlet requirements of the nanofiltration equipment; S2, mixing the qualified pre-treated produced water and the second produced water obtained in S4 to form mixed produced water; S3. Adding a scale inhibitor to the mixed produced water, followed by refined filtration through a first nanofiltration device membrane stack to obtain first produced water and first concentrated water. The first produced water is used for resource utilization of sodium chloride; S4. Add scale inhibitor to the first concentrated water, and then refine and filter it through the second nanofiltration equipment membrane stack to obtain second produced water and second concentrated water. After energy recovery, the second concentrated water is recycled or discharged. The second produced water is reused and mixed with the qualified pretreated produced water from S2.

2. The nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine according to claim 1, characterized in that: Qualified pre-treated water index: SDI 15 Less than 3, ORP less than 300mv, residual chlorine less than 0.1ppm, iron ion less than 0.05mg / L.

3. The nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine according to claim 1, wherein: The addition amount of S3 antiscalant is 2~5ppm, and the supplementary addition amount of S4 antiscalant is 0~5ppm; and / or The liquid after adding the scale inhibitor is pressurized and enters the first nanofiltration device or the second nanofiltration device.

4. The nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated by-product brine according to claim 1, characterized in that: The calcium ion content of the first produced water is less than 150 mg / L, the magnesium ion content is less than 300 mg / L, and the sulfate ion content is less than 200 mg / L; and / or The calcium ion content of the second produced water is similar to that of the qualified pretreated produced water.

5. The nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine according to claim 1, characterized in that: The steps of S1 desalination of by-product concentrated brine include: S1-1, taking concentrated seawater as a by-product of thermal desalination and concentrated seawater as a by-product of membrane desalination, combining them and introducing them into an inlet buffer tank for mixing to produce mixed concentrated seawater; S1-2. The mixed concentrated seawater is filtered into a sand filter to produce synthetic pretreated product water.

6. The nanofiltration process for improving the utilization efficiency of sodium chloride resources in desalinated brine according to claim 5, characterized in that: S1-1 The volume of concentrated seawater produced as a by-product of membrane desalination is 0.2 to 4 times the volume of concentrated seawater produced as a by-product of thermal desalination; and / or By adjusting the inlet flow ratio of concentrated seawater as a by-product of thermal seawater desalination and concentrated seawater as a by-product of membrane seawater desalination, the outlet temperature of the mixed concentrated seawater in the inlet buffer tank is controlled at 25±5°C; when the external ambient temperature is higher than 30°C, the inlet flow ratio of concentrated seawater as a by-product of thermal seawater desalination and concentrated seawater as a by-product of membrane seawater desalination is adjusted to control the temperature of the mixed concentrated seawater entering the buffer tank at 23±2°C.

7. A nanofiltration treatment system for improving the utilization efficiency of sodium chloride in desalinated brine, characterized in that: It includes a pretreatment subsystem, a mixed water production tank, a first nanofiltration device, a concentrated water buffer tank and a second nanofiltration device. The pretreatment subsystem is connected to the mixed water production tank, the mixed water production tank is connected to the first nanofiltration device, the first nanofiltration device and the second nanofiltration device are both provided with a water production pipeline and a concentrated water pipeline, the concentrated water pipeline of the first nanofiltration device is connected to the concentrated water buffer tank, the concentrated water buffer tank is connected to the second nanofiltration device, and the water production pipeline of the second nanofiltration device is connected to the mixed water production tank.

8. The nanofiltration treatment system for improving the resource utilization efficiency of sodium chloride in desalinated brine according to claim 7, characterized in that: The first nanofiltration device includes a raw water pump, a high-pressure pump, a dosing device and a first nanofiltration device. The two ends of the raw water pump are respectively connected to the mixed water production tank and the high-pressure pump. The dosing device is installed on the connecting pipe between the raw water pump and the high-pressure pump. The high-pressure pump is also connected to the first nanofiltration device; the second nanofiltration device has the same structure as the first nanofiltration device, and its nanofiltration device is named the second nanofiltration device.

9. The nanofiltration treatment system for improving the resource utilization efficiency of sodium chloride in desalinated brine according to claim 8, characterized in that: The recovery rate of the first nanofiltration device is controlled at 70% to 80%, the calcium ion removal rate of the first nanofiltration device is controlled at 80% to 92%, the magnesium ion removal rate is controlled at 88% to 98%, the sulfate removal rate is controlled at 96% to 100%, and the sodium chloride retention rate is controlled at 0.2% to 6%; and / or The maximum flux of the first nanofiltration device is 38L / m 2 .h, stable desalination rate ≥99.2%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600 psi; and / or The flux of the nanofiltration membrane element of the first nanofiltration device is controlled at 6~25L / m 2 .h, the water inflow of a single membrane element is controlled at 5~10m 3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~4.5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 5%~12%; the overall recovery rate of the first nanofiltration device is controlled at 70%~80%.

10. The nanofiltration treatment system for improving the utilization efficiency of sodium chloride resources in desalinated brine according to claim 7, characterized in that: The recovery rate of the second nanofiltration device is controlled at 30% to 80%, the calcium ion removal rate of the second nanofiltration device is controlled at 70% to 90%, the magnesium ion removal rate is controlled at 72% to 95%, the sulfate removal rate is controlled at 92% to 99%, and the sodium chloride retention rate is controlled at -2% to 5%; and / or The maximum flux of the second nanofiltration device is 40L / m 2 .h, stable desalination rate ≥98%, maximum inlet water temperature 45℃, maximum inlet water SDI 15 5. The functional layer is made of polypiperazineamide and the membrane shell pressure rating is 600 psi; and / or The flux of the nanofiltration membrane element of the second nanofiltration device is controlled at 3~30L / m 2 .h, the water inflow of a single membrane element is controlled at 5~15m 3 / h, the concentrated water flow rate of the end single membrane element is controlled at 3.5~5m 3 / h, the recovery rate of a single nanofiltration membrane element is controlled at 2%~12%, and the overall recovery rate of the second nanofiltration device is controlled at 30%~80%.

Images