CN211620231U - Device for efficient desalination and comprehensive utilization of seawater - Google Patents
Device for efficient desalination and comprehensive utilization of seawater Download PDFInfo
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- CN211620231U CN211620231U CN201922121974.6U CN201922121974U CN211620231U CN 211620231 U CN211620231 U CN 211620231U CN 201922121974 U CN201922121974 U CN 201922121974U CN 211620231 U CN211620231 U CN 211620231U
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
The utility model discloses a device for high-efficiency desalination and comprehensive utilization of seawater, which comprises a pretreatment unit, a nanofiltration unit, a reverse osmosis seawater desalination unit and a nanofiltration concentrated water utilization unit which are connected with each other, wherein a mechanical filter is arranged behind the pretreatment unit, and the mechanical filter is provided with a clear liquid reflux pipeline connected to the inlet of the pretreatment unit; the first-stage nanofiltration device and the second-stage nanofiltration device of the nanofiltration unit are respectively provided with a concentrated water pipeline connected with the calcium sulfate reactor; the high-pressure reverse osmosis seawater desalination device of the reverse osmosis seawater desalination unit is provided with a produced water return pipeline connected to the inlet of the reverse osmosis seawater desalination device; the nanofiltration concentrated water utilization unit comprises a calcium sulfate reactor, a calcium sulfate separator, a magnesium hydroxide reactor, a magnesium hydroxide separator, an evaporation concentrator and an evaporation crystallizer which are connected in sequence, wherein the evaporation concentrator is provided with a backflow pipeline connected with the calcium sulfate reactor. The fresh water yield of the utility model can be improved to more than 69 percent from about 45 percent of the desalination of the common seawater by the full-film method.
Description
Technical Field
The utility model relates to a device of high-efficient desalination of sea water and comprehensive utilization specifically is a device that improves fresh water product water rate and concentrated seawater comprehensive utilization ratio among the sea water desalination process.
Background
The global water reserves are abundant, but 96.5 percent of the water reserves are seawater, the fresh water resources are relatively short, more than 80 countries and regions have insufficient fresh water, the amount of the Chinese-average fresh water resources is only 1/4 which is the same as the world per capita, and the fresh water resources are very deficient. The seawater contains abundant water resources, almost all elements on the earth, and more than 80 elements are measured at present to form various organic matters and inorganic matters in the seawater. Wherein the elements with content of more than 1mg/kg include 12 kinds, i.e. sodium, potassium, magnesium, calcium, strontium, chlorine, sulfur, bromine, carbon, boron, silicon and fluorine. Therefore, the comprehensive utilization of other useful components while obtaining fresh water from seawater is significant.
At present, the technical level of seawater desalination is continuously improved, the cost is gradually reduced, and a distillation method, a reverse osmosis method, an electrodialysis method and the like are industrially applied on a large scale. Many researches on seawater desalination also have comprehensive utilization of concentrated seawater, but the fresh water recovery rate is generally less than 60%, concentrated seawater can not be effectively utilized frequently, and the seawater utilization efficiency is still low. The comprehensive utilization of various resources in seawater while improving the efficiency of seawater desalination is an important direction for seawater desalination in the future.
Chinese patent CN1994904A discloses a nanofiltration seawater desalination method and device, wherein nanofiltration is added before reverse osmosis, the reverse osmosis seawater desalination water yield is improved to a certain extent, and the operation pressure is reduced, but the concentration of divalent ions in nanofiltration water production is still higher due to the influence of scaling factors, the improvement of the fresh water recovery rate in the reverse osmosis process is limited, and meanwhile, the problem of comprehensive utilization of concentrated seawater is not involved.
Disclosure of Invention
The to-be-solved technical problem of the utility model is to provide a device of high-efficient desalination of sea water and comprehensive utilization, can improve the water yield of sea water desalination through the device, draw materials such as sodium chloride, calcium sulfate, magnesium hydroxide, bromine simultaneously from the sea water, comprehensive utilization the principal ingredients in the sea water, sea water comprehensive utilization improves greatly.
In order to solve the technical problem, the utility model comprises four parts of a pretreatment unit, a nanofiltration unit, a reverse osmosis seawater desalination unit and a nanofiltration concentrated water utilization unit which are connected with each other, wherein the pretreatment unit comprises a sterilization device, an air floatation or a coagulating sedimentation device, a microfiltration and/or an ultrafiltration device which are connected in sequence, a mechanical filter is arranged behind the pretreatment unit, the mechanical filter is provided with a clear liquid backflow pipeline connected to the inlet of the pretreatment unit, and is also provided with a waste residue outlet; the nanofiltration unit comprises a primary nanofiltration device and a secondary nanofiltration device which are connected in sequence, the secondary nanofiltration device is provided with a water production pipeline connected to a reverse osmosis seawater desalination device, and the primary nanofiltration device and the secondary nanofiltration device are respectively provided with a concentrated water pipeline connected with a calcium sulfate reactor; the reverse osmosis seawater desalination unit comprises a reverse osmosis seawater desalination device and a high-pressure reverse osmosis seawater desalination device which are sequentially connected, the high-pressure reverse osmosis seawater desalination device is provided with a produced water return pipeline connected to the inlet of the reverse osmosis seawater desalination device, a concentrated water pipeline connected to a bromine extraction device, and the bromine extraction device is provided with a concentrated water pipeline connected to a brine tank; the nanofiltration concentrated water utilization unit comprises a calcium sulfate reactor, a calcium sulfate separator, a magnesium hydroxide reactor, a magnesium hydroxide separator, an evaporation concentrator and an evaporation crystallizer which are sequentially connected, wherein the calcium sulfate separator and the magnesium hydroxide separator are respectively provided with a product outlet, and the evaporation concentrator is provided with a reflux pipeline connected with the calcium sulfate reactor; the reverse osmosis device, the evaporation concentrator and the evaporation crystallizer are all provided with water production pipelines connected to the fresh water tank.
The microfiltration device of the pretreatment unit adopts a sand filter or a fiber bundle filter or a self-cleaning filter or a disc filter, the ultrafiltration device adopts an inorganic ultrafiltration membrane or an organic ultrafiltration membrane, the filtration pore diameter is 20-1000 nm, the filtration temperature is 5-40 ℃, the membrane surface flow rate is 0.5-5 m/s, and the filtration pressure is 0.05-0.5 MPa. The pretreatment unit is preferably a combined form in which an air floatation device, a microfiltration device and an ultrafiltration device are sequentially connected.
The pretreatment units are respectively provided with a concentrated water pipeline connected with a mechanical filter, the mechanical filter is connected with a seawater intake pipeline through a clear liquid backflow pipeline, the concentrated water generated by each pretreatment unit is collected and then filtered by the mechanical filter to remove solid impurities, and the clear liquid and the original seawater are mixed for recycling. Preferably, a filter press is used as the mechanical filter.
The primary nanofiltration device and the secondary nanofiltration device of the nanofiltration unit select a hollow fiber nanofiltration membrane or a rolled nanofiltration membrane; the membrane material is selected from polyethersulfone, polyamide, polysulfone, sulfonated polysulfone or composite material.
The first-stage nanofiltration device has the filtration precision of 500-1000 Da of molecular weight cut-off, wherein SO is treated4 2-The retention rate of the calcium carbonate is 90-97%, and the calcium carbonate is calcium carbonate2+The rejection rate is 10-40%, the operation pressure is 1.0-3.5 MPa, and the recovery rate of the device is controlled to be 80-88%; the secondary nanofiltration device has the filtration precision of the cut-off molecular weight of 200-600 Da, wherein the SO is treated4 2-The retention rate of Ca is more than 98 percent2+The rejection rate is 75-86%, the system operating pressure is 2.5-4.0 MPa, and the device recovery rate is controlled to be 90-96%.
The reverse osmosis seawater desalination device of the reverse osmosis seawater desalination unit is connected with the high-pressure reverse osmosis seawater desalination device through a concentrated water pipeline, the operating pressure of the reverse osmosis seawater desalination device is 5.0-6.5 MPa, the reverse osmosis desalination rate is greater than 95%, the operating pressure of the high-pressure reverse osmosis seawater desalination device is 7.0-9.0 MPa, and the high-pressure reverse osmosis desalination rate is 90-98%.
The calcium sulfate reactor and the magnesium hydroxide reactor have the functions of gas explosion or stirring.
The utility model discloses the working process includes following step:
(1) taking raw seawater for pretreatment, firstly sterilizing, then entering an air floatation or coagulating sedimentation device, then filtering produced water by a microfiltration and/or ultrafiltration device to obtain pretreated seawater, collecting concentrated water produced by the pretreatment devices, mechanically filtering to remove solid impurities, and returning to be mixed with the raw seawater for reuse;
(2) adding a scale inhibitor into the seawater pretreated in the step (1), pressurizing the seawater to enter a primary nanofiltration device, adjusting the pH value of primary nanofiltration produced water to 3-7, and pressurizing the water to enter a secondary nanofiltration device;
(3) the concentrated water subjected to the first-stage nanofiltration and the concentrated water subjected to the second-stage nanofiltration in the step (2) enter a calcium sulfate reactor, and meanwhile, calcium chloride solution with the excessive concentration of 20-28 wt% is added to serve as SO in a mixed solution of a precipitator and the concentrated water4 2-Fully reacting to generate calcium sulfate precipitate, performing solid-liquid separation by a calcium sulfate separator, and then washing and drying to obtain solid calcium sulfate; the reacted mother liquor enters a magnesium hydroxide reactor, and lime emulsion with the concentration of 15-26 wt% and Mg in the mother liquor are added2+Reacting to generate magnesium hydroxide precipitate, carrying out solid-liquid separation by a magnesium hydroxide separator, washing and drying to obtain solid magnesium hydroxide; after magnesium is extracted, the main components of mother liquor are calcium chloride and sodium chloride, the mother liquor enters an evaporation concentrator after the pH value is adjusted to 7-8, when the concentration of the calcium chloride in the mother liquor reaches 20-28 wt% in the evaporation process, part of the mother liquor is used as a precipitator, the calcium chloride solution returns to a calcium sulfate reactor through a backflow pipeline, and the rest of the mother liquor continuously enters an evaporation crystallizer to produce the sodium chloride and the calcium chloride;
(4) and (3) adjusting the pH value of the secondary nanofiltration produced water in the step (2) to 6.5-7.8, pressurizing the water to enter a reverse osmosis seawater desalination device, pressurizing the reverse osmosis concentrated water again to enter a high-pressure reverse osmosis seawater desalination device, returning the high-pressure reverse osmosis produced water to the reverse osmosis seawater desalination device through a return line for continuous desalination, and extracting bromine from the high-pressure reverse osmosis concentrated water through a bromine extraction device and then entering a brine tank.
The raw seawater in the steps (1) to (4) of the method sequentially passes through all devices of the pretreatment unit, the primary nanofiltration device, the secondary nanofiltration device and the reverse osmosis seawater desalination device, and the water produced by the former device is used as the water inlet of the next device. The produced water of the reverse osmosis seawater desalination device is used as the fresh water of the final product, the reverse osmosis concentrated water is used as the inlet water of the high-pressure reverse osmosis, the produced water of the high-pressure reverse osmosis returns to the inlet of the reverse osmosis seawater desalination device, the high-pressure reverse osmosis concentrated water is the salt water with the salt content of more than 10%, and the salt water can be used as the salt water after bromine extraction or can be used as the salt water for producing strong brine or solid sodium chloride through evaporation and.
The pretreatment of the raw seawater in the step (1) of the method comprises the steps of sterilizing, then entering an air floatation or coagulating sedimentation device, and removing 10-3～10-6mm suspended particles or colloid, partial microorganisms, nitrogen, phosphorus and other nutrient-rich substances, heavy metals, organic matter impurities and the like, and then the fine suspended particles, colloid, microorganisms and organic matter impurities in the seawater are further removed by a microfiltration and/or ultrafiltration device, the turbidity of the seawater is reduced, and the turbidity of the pretreated produced water is less than 1 NTU.
In the pretreatment process in the step (1), the wastewater generated in each link is concentrated and enters a mechanical filter through a pipeline to remove solid impurities, a filter press is preferred, the effluent of the press is connected to a pretreatment inlet through a pipeline, the filtered clear liquid is returned to be mixed with the original seawater for reuse, and the solid residue is used as waste residue for harmless treatment.
The scale inhibitor in the step (2) of the method is selected from an organic phosphine series or polycarboxylic acid series environment-friendly scale inhibitor, preferably one or a combination of several of hydroxyethylidene diphosphonic acid scale inhibitor (HEDP), ethylenediamine tetramethylene phosphonic acid (EDTMPA), amino trimethylene phosphonic Acid Tetrasodium (ATMP), polyaspartic acid (sodium) (PASP), polyepoxysuccinic acid (PESA) sodium lignosulfonate and polyacrylic acid (PAA), and the adding amount is 4-15 mg/L, preferably 5-10 mg/L.
The above methodAnd (4) reacting the concentrated water subjected to the first-stage nanofiltration in the step (3) with the concentrated water subjected to the second-stage nanofiltration in a calcium sulfate reactor to produce calcium sulfate. In order to promote the reaction to generate the added precipitant, a process product for producing calcium chloride by evaporating and concentrating mother liquor obtained after separating magnesium hydroxide from concentrated water mixed liquor is adopted, the mother liquor obtained after separating magnesium hydroxide is concentrated in a multi-effect evaporation mode, sodium chloride is continuously separated out in the concentration process, and when the mother liquor is concentrated to the concentration of 20-28 wt% of calcium chloride, part of the solution is returned to the mixed liquor of two-stage nanofiltration concentrated water to remove SO4 2-To make SO4 2-The precipitation is carried out fully, and the precipitator calcium chloride solution needs to be added in excess.
The process for producing magnesium hydroxide in the step (3) of the method takes the mother liquor obtained after calcium sulfate extraction as a raw material, the concentration of the added lime emulsion is preferably 20-25 wt%, and the magnesium hydroxide is produced by filtering, separating, washing and drying after the reaction is completed.
The reverse osmosis seawater desalination device in the step (4) of the method takes the produced water of the secondary nanofiltration as a raw material, and 5-10 wt% of sodium hydroxide or potassium hydroxide solution is added to adjust the pH value to 6.5-7.8, preferably sodium hydroxide solution. The reverse osmosis seawater desalination device adopts a reverse osmosis seawater desalination membrane, and as most of divalent ions are removed, the osmotic pressure is reduced, the flux is increased, and the water yield is greatly improved. The reverse osmosis concentrated water is pressurized to 7.0-9.0 MPa and enters a high-pressure reverse osmosis seawater desalination device for secondary concentration and desalination, the high-pressure reverse osmosis pressure is preferably 7.6-8.5 MPa, and the high-pressure reverse osmosis desalination rate is preferably more than 93%. The salt content of the produced water of the high-pressure reverse osmosis is 0.5-1.5 wt%, and the produced water returns to the inlet of the reverse osmosis seawater desalination device in the previous step, so that the recovery rate of seawater desalination is improved.
In the reverse osmosis and high-pressure reverse osmosis seawater desalination device in the step (4), the fresh water yield of the two-stage reverse osmosis is 80-85%, the sodium chloride concentration in the high-pressure reverse osmosis concentrated water reaches 11-16 wt%, the bromine content reaches 270-390 mg/l, and the sodium chloride purity in the concentrated water after bromine extraction is more than 96%.
Adopt the utility model discloses, the sea water enters the two-stage nanofiltration device behind preprocessing device, interception rate through the different divalent ions of substep control, divalent ion's effective desorption has been realized, the water yield among the seawater reverse osmosis sea water desalination process improves greatly after nanofiltration, utilize simultaneously to receive and strain the dense water and extracted calcium sulfate, magnesium hydroxide and calcium chloride, bromine content increases in the high pressure reverse osmosis dense water, can extract bromine, sodium chloride concentration reaches more than 10% in the dense water, and purity is higher, can regard as the salt dissolving water of soda or chlor-alkali, reduce the use amount of raw salt, also can adopt methods evaporation concentration production sodium chloride such as vacuum salt manufacturing. Adopt the utility model provides a device, the water yield of fresh water can improve to more than 69% from about 45% of ordinary sea water full membrane method desalination, realizes the high-efficient desalination of sea water, and the various active ingredients of while comprehensive utilization in the sea water compare dense water emission greatly reduced with conventional sea water desalination, and comprehensive utilization is showing and is improving.
Drawings
The invention will be further described with reference to the following figures and examples:
fig. 1 is a schematic view of the device of the present invention.
Detailed Description
Example 1
Referring to fig. 1, the utility model comprises a pretreatment unit, a nanofiltration unit, a reverse osmosis seawater desalination unit and a nanofiltration concentrated water utilization unit which are connected with each other. The pretreatment unit is a combination of a chlorine dioxide sterilization device, a coagulating sedimentation device, a sand filtration device and an ultrafiltration device, a filter press is arranged behind the pretreatment unit, and the filter press is provided with a clear liquid backflow pipeline connected to an inlet of the pretreatment unit and a waste residue outlet; the nanofiltration unit comprises a primary nanofiltration device and a secondary nanofiltration device which are connected in sequence, the secondary nanofiltration device is provided with a water production pipeline connected to a reverse osmosis seawater desalination device, and the primary nanofiltration device and the secondary nanofiltration device are respectively provided with a concentrated water pipeline connected with a calcium sulfate reactor; the reverse osmosis seawater desalination unit comprises a reverse osmosis seawater desalination device and a high-pressure reverse osmosis seawater desalination device which are sequentially connected, the high-pressure reverse osmosis seawater desalination device is provided with a produced water return pipeline connected to the inlet of the reverse osmosis seawater desalination device, a concentrated water pipeline connected to a bromine extraction device, and the bromine extraction device is provided with a concentrated water pipeline connected to a brine tank; the nanofiltration concentrated water utilization unit comprises a calcium sulfate reactor, a calcium sulfate separator, a magnesium hydroxide reactor, a magnesium hydroxide separator, an evaporation concentrator and an evaporation crystallizer which are sequentially connected, wherein the calcium sulfate separator and the magnesium hydroxide separator are respectively provided with a product outlet, and the evaporation concentrator is provided with a reflux pipeline connected with the calcium sulfate reactor; the reverse osmosis device, the evaporation concentrator and the evaporation crystallizer are all provided with water production pipelines connected to the fresh water tank. The calcium sulfate reactor and the magnesium hydroxide reactor both have the function of gas explosion or stirring.
Taking a seawater desalination device for carrying out fresh water harvest 10000m per day as an example, the typical components of seawater are as follows:
| composition (I) | K+ | Na+ | Ca2+ | Mg2+ | Sr2+ | Cl- | SO4 2- | HCO3 - | F- | Br- |
| mg/L | 399 | 10770 | 412 | 1290 | 7.9 | 19354 | 2714 | 142 | 1.3 | 67.3 |
The water intake of the raw seawater is 570m3Sterilizing by chlorine dioxide, performing coagulating sedimentation for preliminary purification to remove part of suspended particulate matters or colloids, further removing impurities such as fine suspended particulate matters, colloids, microorganisms, organic matters and the like in the seawater by sand filtration and ultrafiltration, and reducing the turbidity of the seawater to below 1 NTU; mixing concentrated water discharged by coagulating sedimentation, sand filtration and ultrafiltration, filtering by a filter press, squeezing solid residues, then harmlessly burning, returning filtered clear liquid to be mixed with the original seawater for reuse, improving the utilization rate of the seawater, and taking away the seawater external discharge capacity of 11m by the seawater pretreatment solid waste3/h。
Adding 5mg/L of high-efficiency scale inhibitor into the pretreated seawater, pressurizing the seawater, and filtering the seawater in a first-stage nanofiltration device, wherein the filtering precision is the cut-off molecular weight of 600-800 Da, and SO is treated4 2-The retention rate of (2) to Ca is 96.5%2+The rejection rate is 26%, the system operation pressure is 2.1-3.0 MPa, and the recovery rate of the primary nanofiltration is controlled at 84%; adding 5wt% of hydrochloric acid into the primary nanofiltration water to adjust the pH value to 5-6, pressurizing the water to enter a secondary nanofiltration device, wherein the filtration precision of the selected nanofiltration membrane is 200-300 Da of the cut-off molecular weight, and SO is treated4 2-A retention rate of 99% for Mg2+Retention rate of 90% for Ca2+The rejection rate is 86%, the system operation pressure is 2.5-3.0 MPa, and the recovery rate of the secondary nanofiltration is controlled at 91%.
The first-stage nanofiltration concentrated water and the second-stage nanofiltration concentrated water enter a calcium sulfate reactor to be mixed and stirred, white calcium sulfate precipitation appears in the mixed solution, and simultaneously, a 23wt% calcium chloride solution with the thickness of 28.8m is additionally added3H promoting SO in the concentrated water4 2-Fully reacting, carrying out solid-liquid separation in a calcium sulfate separator, washing and drying to obtain 2.1t/h calcium sulfate; the mother liquor after the reaction enters a magnesium hydroxide reactor, and 25wt% of lime emulsion 8m is added3H and Mg in mother liquor2+Reacting to generate magnesium hydroxide precipitate, carrying out solid-liquid separation in a magnesium hydroxide separator, washing and drying to obtain magnesium hydroxide of 1.7 t/h; the mother liquor after magnesium extraction enters an evaporation concentrator to be concentrated through multi-effect evaporation, and part of the mother liquor after the calcium chloride concentration reaches 23wt% in the evaporation process is used as calcium chloride supplement liquid according to the length of 24m3The reaction product is returned to the calcium sulfate reactor for removing SO in the concentrated water mixed liquor4 2-And the residual mother liquor continues to enter an evaporation crystallizer to produce sodium chloride and calcium chloride.
Adjusting the pH value of the water produced by the secondary nanofiltration to 6.5-7.0 by using a 5wt% sodium hydroxide solution, pressurizing the water to enter a reverse osmosis seawater desalination device, wherein the operating pressure is 5.0-5.5 MPa, and the reverse osmosis desalination rate is 95-96%; the reverse osmosis concentrated water is pressurized again and enters a high-pressure reverse osmosis seawater desalination device, the operating pressure is 7.0-7.5 MPa, the high-pressure reverse osmosis desalination rate is 90-93%, the salt content of the high-pressure reverse osmosis fresh water is high, and the high-pressure reverse osmosis concentrated water returns to the inlet of the reverse osmosis seawater desalination device for further desalination; the fresh water passes through a reverse osmosis unit and a high-pressure reverse osmosis unit to obtain fresh water with the water volume of 370m3And h, the water yield is 84%, the sodium chloride concentration in the high-pressure reverse osmosis concentrated water is 15wt%, the bromine content reaches 390mg/l, the sodium chloride purity in the concentrated water after bromine extraction by adopting an air bromine blowing method is more than 96%, and the concentrated water is sent to a brine tank to be used as brine.
Under the working condition, the total yield of fresh water is 73 percent, and the comprehensive utilization rate of seawater is 87 percent.
Example 2
The device of the embodiment is basically the same as that of the embodiment 1, and the main difference is that the pretreatment unit adopts the combination of an electrolytic chlorine preparation sterilization device, an air floatation device, a self-cleaning filter and an ultrafiltration device.
Taking a seawater desalination device for carrying out fresh water harvest 10000m per day as an example, the typical components of seawater are as follows:
| composition (I) | K+ | Na+ | Ca2+ | Mg2+ | Sr2+ | Cl- | SO4 2- | HCO3 - | F- | Br- |
| mg/L | 278 | 10212 | 641 | 1637 | 7.9 | 19978 | 3011 | 263 | 1.3 | 56.4 |
The water intake of the original seawater is 600m3Firstly, after electrolytic chlorine preparation sterilization, the seawater enters air floatation primary purification to remove part of suspended particulate matters or colloids, and then is subjected to self-cleaning filter and ultrafiltration to further remove impurities such as fine suspended particulate matters, colloids, microorganisms, organic matters and the like in the seawater, so that the turbidity of the seawater is reduced to below 1.2 NTU; the concentrated water discharged by air floatation and ultrafiltration is mixed and filtered by a filter press, solid residues are squeezed and then harmlessly burned, the filtered clear liquid is returned to be mixed with the original seawater for reuse, the utilization rate of the seawater is improved, and the seawater external discharge capacity is taken away by the seawater pretreatment solid waste3/h。
Adding 13mg/L of high-efficiency scale inhibitor into the pretreated seawater, pressurizing the seawater, and filtering the seawater in a first-stage nanofiltration device, wherein the filtering precision is the cut-off molecular weight of 500-700 Da, and SO is treated4 2-A retention rate of 91% for Ca2+The rejection rate is 39%, the system operation pressure is 2.7-3.4 MPa, and the recovery rate of the primary nanofiltration is controlled at 81%; adding 5wt% of hydrochloric acid into the primary nanofiltration water to adjust the pH value to 6-7, pressurizing the water to enter a secondary nanofiltration device, wherein the filtration precision of the selected nanofiltration membrane is 200-300 Da of the cut-off molecular weight, and SO is treated4 2-A retention rate of 98% for Mg2+A retention rate of 85% for Ca2+The rejection rate is 80%, the system operation pressure is 2.8-3.5 MPa, and the recovery rate of the secondary nanofiltration is controlled at 93%.
The first-stage nanofiltration concentrated water and the second-stage nanofiltration concentrated water enter a calcium sulfate reactor to be mixed and stirred, white calcium sulfate precipitation appears in the mixed solution, and simultaneously, a calcium chloride solution with the weight percent of 27 percent is additionally added for 25m3H promoting SO in the concentrated water4 2-Fully reacting, carrying out solid-liquid separation in a calcium sulfate separator, washing and drying to obtain 2.5t/h calcium sulfate; the mother liquor after the reaction enters a magnesium hydroxide reactor, and 20wt% of lime emulsion 14m is added3H and Mg in mother liquor2+Reacting to generate magnesium hydroxide precipitate, and solidifying in a magnesium hydroxide separatorAfter liquid separation, washing and drying to obtain 2.2t/h magnesium hydroxide; the mother liquor after magnesium extraction enters an evaporation concentrator to be concentrated through multi-effect evaporation, and part of the mother liquor after the calcium chloride concentration reaches 27wt% in the evaporation process is used as calcium chloride supplement liquid according to the volume of 25m3The reaction product is returned to the calcium sulfate reactor for removing SO in the concentrated water mixed liquor4 2-And the residual mother liquor continues to enter an evaporation crystallizer to produce sodium chloride and calcium chloride.
Adjusting the pH value of the water produced by the secondary nanofiltration to 6.8-7.5 by using a 5wt% sodium hydroxide solution, pressurizing the water to enter a reverse osmosis seawater desalination device, wherein the operating pressure is 6.0-6.5 MPa, and the reverse osmosis desalination rate is more than 99%; the reverse osmosis concentrated water is pressurized again and enters a high-pressure reverse osmosis seawater desalination device, the operating pressure is 8.0-8.5 MPa, the high-pressure reverse osmosis desalination rate is 95-96%, the salt content of the high-pressure reverse osmosis fresh water is high, and the high-pressure reverse osmosis concentrated water returns to an inlet of the reverse osmosis seawater desalination device for further desalination; the fresh water passes through a reverse osmosis unit and a high-pressure reverse osmosis unit, and the fresh water yield is 360m3And h, the water yield is 80%, the concentration of sodium chloride in the high-pressure reverse osmosis concentrated water is 13.5wt%, the content of bromine reaches 270mg/l, the purity of sodium chloride in the concentrated water after bromine extraction by adopting an air bromine blowing method is more than 96%, and the concentrated water is sent to a brine tank to be used as brine.
Under the working condition, the total yield of fresh water is 69 percent, and the comprehensive utilization rate of seawater is 84 percent.
Claims (6)
1. A device for efficient desalination and comprehensive utilization of seawater is characterized by comprising four parts, namely a pretreatment unit, a nanofiltration unit, a reverse osmosis seawater desalination unit and a nanofiltration concentrated water utilization unit which are connected with one another, wherein the pretreatment unit comprises a sterilization device, an air flotation or coagulating sedimentation device and a microfiltration and/or ultrafiltration device which are connected in sequence; the nanofiltration unit comprises a primary nanofiltration device and a secondary nanofiltration device which are connected in sequence, the secondary nanofiltration device is provided with a water production pipeline connected to a reverse osmosis seawater desalination device, and the primary nanofiltration device and the secondary nanofiltration device are respectively provided with a concentrated water pipeline connected with a calcium sulfate reactor; the reverse osmosis seawater desalination unit comprises a reverse osmosis seawater desalination device and a high-pressure reverse osmosis seawater desalination device which are sequentially connected, the high-pressure reverse osmosis seawater desalination device is provided with a produced water return pipeline connected to the inlet of the reverse osmosis seawater desalination device, a concentrated water pipeline connected to a bromine extraction device, and the bromine extraction device is provided with a concentrated water pipeline connected to a brine tank; the nanofiltration concentrated water utilization unit comprises a calcium sulfate reactor, a calcium sulfate separator, a magnesium hydroxide reactor, a magnesium hydroxide separator, an evaporation concentrator and an evaporation crystallizer which are sequentially connected, wherein the calcium sulfate separator and the magnesium hydroxide separator are respectively provided with a product outlet, and the evaporation concentrator is provided with a reflux pipeline connected with the calcium sulfate reactor; the reverse osmosis device, the evaporation concentrator and the evaporation crystallizer are all provided with water production pipelines connected to the fresh water tank.
2. The device for seawater desalination and comprehensive utilization according to claim 1, wherein the microfiltration device in the pretreatment unit adopts a sand filter, a fiber bundle filter, a self-cleaning filter or a disc filter, the ultrafiltration device adopts an inorganic ultrafiltration membrane or an organic ultrafiltration membrane, the filtration pore size is 20-1000 nm, the filtration temperature is 5-40 ℃, the membrane surface flow rate is 0.5-5 m/s, and the filtration pressure is 0.05-0.5 MPa.
3. The device for seawater desalination and comprehensive utilization as claimed in claim 1 or 2, wherein each device of the pretreatment unit is provided with a concentrated water pipeline connected with a mechanical filter, and the mechanical filter is connected with a seawater intake pipeline through a clear liquid return pipeline.
4. The device for seawater desalination and comprehensive utilization as claimed in claim 1, wherein the nanofiltration unit comprises two nanofiltration devices connected in sequence, the first nanofiltration device is connected to the second nanofiltration device via a water production line, and the filtration precision of the first nanofiltration device is 500-1000 Da, wherein SO is introduced into the first nanofiltration device4 2-The retention rate of the calcium carbonate is 90-97%, and the calcium carbonate is calcium carbonate2+The rejection rate is 10-40%, the operation pressure is 1.0-3.5 MPa, and the recovery rate of the device is 80-88%; the filtration precision of the secondary nanofiltration device is 200-600 Da of the molecular weight cut-off, wherein the SO is4 2-The retention rate of Ca is more than 98 percent2+The rejection rate is 75-86%, the operation pressure is 2.5-4.0 MPa, and the recovery rate of the device is 90-96%.
5. The device for efficient desalination and comprehensive utilization of seawater according to claim 1, wherein the reverse osmosis seawater desalination unit comprises two stages of reverse osmosis devices which are connected in sequence, the reverse osmosis seawater desalination device is connected with the high-pressure reverse osmosis seawater desalination device through a concentrated water pipeline, the operating pressure of the reverse osmosis seawater desalination device is 5.0-6.5 MPa, and the operating pressure of the high-pressure reverse osmosis seawater desalination device is 7.0-9.0 MPa.
6. The device for efficiently desalinating and comprehensively utilizing seawater according to claim 1, wherein the calcium sulfate reactor and the magnesium hydroxide reactor are provided with a gas explosion or stirring function.
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| CN111003717A (en) * | 2019-11-20 | 2020-04-14 | 常州大学 | Device and method for preparing alkali salt by evaporating and crystallizing sea water desalination strong brine |
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