CN112591770A - Process and apparatus for purifying and separating potassium sulfate from light salt water - Google Patents
Process and apparatus for purifying and separating potassium sulfate from light salt water Download PDFInfo
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- CN112591770A CN112591770A CN202011072923.XA CN202011072923A CN112591770A CN 112591770 A CN112591770 A CN 112591770A CN 202011072923 A CN202011072923 A CN 202011072923A CN 112591770 A CN112591770 A CN 112591770A
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- nanofiltration
- membrane
- potassium sulfate
- potassium
- salt
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- 229910052939 potassium sulfate Inorganic materials 0.000 title claims abstract description 73
- OTYBMLCTZGSZBG-UHFFFAOYSA-L potassium sulfate Chemical compound [K+].[K+].[O-]S([O-])(=O)=O OTYBMLCTZGSZBG-UHFFFAOYSA-L 0.000 title claims abstract description 71
- 235000011151 potassium sulphates Nutrition 0.000 title claims abstract description 71
- 150000003839 salts Chemical class 0.000 title claims abstract description 66
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 46
- 230000008569 process Effects 0.000 title claims abstract description 37
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 claims abstract description 146
- 238000001728 nano-filtration Methods 0.000 claims abstract description 102
- 239000012267 brine Substances 0.000 claims abstract description 70
- 239000001103 potassium chloride Substances 0.000 claims abstract description 70
- 235000011164 potassium chloride Nutrition 0.000 claims abstract description 70
- 239000000243 solution Substances 0.000 claims abstract description 57
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims abstract description 55
- 238000004519 manufacturing process Methods 0.000 claims abstract description 13
- 238000001704 evaporation Methods 0.000 claims abstract description 11
- 238000010790 dilution Methods 0.000 claims abstract description 10
- 239000012895 dilution Substances 0.000 claims abstract description 10
- 238000007865 diluting Methods 0.000 claims abstract description 6
- 239000012528 membrane Substances 0.000 claims description 166
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 75
- 239000012510 hollow fiber Substances 0.000 claims description 55
- 239000007788 liquid Substances 0.000 claims description 42
- 238000000926 separation method Methods 0.000 claims description 40
- 230000004907 flux Effects 0.000 claims description 35
- 239000012530 fluid Substances 0.000 claims description 32
- 230000000149 penetrating effect Effects 0.000 claims description 32
- 238000001914 filtration Methods 0.000 claims description 24
- 239000002244 precipitate Substances 0.000 claims description 23
- VKJKEPKFPUWCAS-UHFFFAOYSA-M potassium chlorate Chemical compound [K+].[O-]Cl(=O)=O VKJKEPKFPUWCAS-UHFFFAOYSA-M 0.000 claims description 19
- 239000011575 calcium Substances 0.000 claims description 18
- 239000012466 permeate Substances 0.000 claims description 15
- 239000011148 porous material Substances 0.000 claims description 15
- 239000011734 sodium Substances 0.000 claims description 15
- 238000002425 crystallisation Methods 0.000 claims description 13
- 230000008025 crystallization Effects 0.000 claims description 13
- 229910001425 magnesium ion Inorganic materials 0.000 claims description 13
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 claims description 12
- 238000001556 precipitation Methods 0.000 claims description 12
- 238000007789 sealing Methods 0.000 claims description 12
- 239000002994 raw material Substances 0.000 claims description 10
- 150000002500 ions Chemical class 0.000 claims description 9
- 239000004952 Polyamide Substances 0.000 claims description 8
- 229920002647 polyamide Polymers 0.000 claims description 8
- 230000009467 reduction Effects 0.000 claims description 8
- 238000003860 storage Methods 0.000 claims description 8
- 230000008020 evaporation Effects 0.000 claims description 5
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 3
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 3
- 229910001424 calcium ion Inorganic materials 0.000 claims description 3
- 239000000460 chlorine Substances 0.000 claims description 3
- 229910052801 chlorine Inorganic materials 0.000 claims description 3
- 239000012141 concentrate Substances 0.000 claims description 3
- 239000003292 glue Substances 0.000 claims description 3
- 229910017053 inorganic salt Inorganic materials 0.000 claims description 3
- 239000012452 mother liquor Substances 0.000 claims description 3
- 238000010979 pH adjustment Methods 0.000 claims description 3
- 239000004642 Polyimide Substances 0.000 claims description 2
- 229920002301 cellulose acetate Polymers 0.000 claims description 2
- 238000004090 dissolution Methods 0.000 claims description 2
- 229920002492 poly(sulfone) Polymers 0.000 claims description 2
- 229920002239 polyacrylonitrile Polymers 0.000 claims description 2
- 229920000728 polyester Polymers 0.000 claims description 2
- 229920001721 polyimide Polymers 0.000 claims description 2
- 229920000642 polymer Polymers 0.000 claims description 2
- 229920002554 vinyl polymer Polymers 0.000 claims description 2
- 238000005868 electrolysis reaction Methods 0.000 abstract description 11
- 239000000126 substance Substances 0.000 abstract description 8
- 239000003513 alkali Substances 0.000 abstract description 3
- 238000002360 preparation method Methods 0.000 abstract description 2
- 235000011121 sodium hydroxide Nutrition 0.000 description 22
- 239000013078 crystal Substances 0.000 description 18
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 11
- 239000011780 sodium chloride Substances 0.000 description 11
- 239000008367 deionised water Substances 0.000 description 8
- 229910021641 deionized water Inorganic materials 0.000 description 8
- 238000001035 drying Methods 0.000 description 8
- 238000001816 cooling Methods 0.000 description 7
- 238000002156 mixing Methods 0.000 description 7
- CDBYLPFSWZWCQE-UHFFFAOYSA-L sodium carbonate Substances [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 7
- 229910000029 sodium carbonate Inorganic materials 0.000 description 7
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 6
- 230000000903 blocking effect Effects 0.000 description 6
- 239000000919 ceramic Substances 0.000 description 6
- 238000006298 dechlorination reaction Methods 0.000 description 6
- 239000011777 magnesium Substances 0.000 description 6
- 238000001471 micro-filtration Methods 0.000 description 6
- 230000001376 precipitating effect Effects 0.000 description 6
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 239000002245 particle Substances 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- 238000001514 detection method Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 229940072033 potash Drugs 0.000 description 3
- BWHMMNNQKKPAPP-UHFFFAOYSA-L potassium carbonate Substances [K+].[K+].[O-]C([O-])=O BWHMMNNQKKPAPP-UHFFFAOYSA-L 0.000 description 3
- 235000015320 potassium carbonate Nutrition 0.000 description 3
- 238000000746 purification Methods 0.000 description 3
- 230000008439 repair process Effects 0.000 description 3
- -1 sulfate radical salt Chemical class 0.000 description 3
- 239000006227 byproduct Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- ZFXVRMSLJDYJCH-UHFFFAOYSA-N calcium magnesium Chemical compound [Mg].[Ca] ZFXVRMSLJDYJCH-UHFFFAOYSA-N 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229920006158 high molecular weight polymer Polymers 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000007689 inspection Methods 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 239000002861 polymer material Substances 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 239000012266 salt solution Substances 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
Images
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
- C01D5/16—Purification
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/44—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis
- C02F1/442—Treatment of water, waste water, or sewage by dialysis, osmosis or reverse osmosis by nanofiltration
Abstract
The invention relates to a production process and a device for purifying and separating potassium sulfate from light salt water, belonging to the technical field of chlor-alkali chemical industry. The method comprises the following steps: step a, performing first nanofiltration on potassium chloride brine to separate monovalent salt and divalent salt; step b, diluting the concentrated solution obtained in the first nanofiltration process by adding water, and then carrying out second nanofiltration to separate monovalent salt and divalent salt; and c, evaporating and crystallizing the concentrated solution obtained by the second nanofiltration to obtain analytically pure potassium sulfate. In one embodiment, in step b, the dilution factor is 3 to 8. The method can reuse the light salt water generated in the potassium chloride electrolysis process, effectively separate the potassium sulfate from the potassium chloride, and can realize the preparation of the potassium sulfate product with analytical purity grade.
Description
Technical Field
The invention relates to a production process and a device for purifying and separating potassium sulfate from light salt water, belonging to the technical field of chlor-alkali chemical industry.
Background
The potassium chloride brine is an aqueous solution containing potassium chloride, potassium sulfate and possibly potassium chlorate, and the most typical potassium chloride brine system is provided with a brine refining system required in the processes of preparing refined potassium chloride and preparing potassium hydroxide, wherein the refined potassium chloride is mainly used for producing ultrapure potassium chloride, pharmaceutical-grade potassium chloride, food-grade potassium chloride, edible potassium chloride and the like required for producing low sodium salt by dissolving, refining and recrystallizing industrial crystalline potassium chloride, and the refining process is mainly used for removing impurities such as calcium magnesium ions, sulfate ions and the like; the potassium chloride brine refining system for producing the ionic membrane potash is low-concentration potassium chloride brine generated by electrolyzing potassium chloride brine, commonly called light brine, wherein: the concentrations of the individual components were as follows: 120-220 g/l of potassium chloride, 3-13 g/l of potassium sulfate and 2-20 g/l of potassium chlorate.
However, how to utilize the potassium chloride brine and the by-products after electrolysis is a problem in industrial processes.
Disclosure of Invention
The purpose of the invention is: the production of pure-grade potassium sulfate is analyzed by using light brine generated after electrolysis in a potash plant.
The technical scheme is as follows:
the process for producing potassium sulfate comprises the following steps:
step a, performing first nanofiltration on potassium chloride brine to separate monovalent salt and divalent salt;
step b, diluting the concentrated solution obtained in the first nanofiltration process by adding water, and then carrying out second nanofiltration to separate monovalent salt and divalent salt;
and c, evaporating and crystallizing the concentrated solution obtained by the second nanofiltration to obtain analytically pure potassium sulfate.
In one embodiment, in step b, the dilution factor is 3 to 8.
In one embodiment, in the step a, the weak brine of potassium chloride contains 120-220 g/l of potassium chloride, 3-13 g/l of potassium sulfate and 2-20 g/l of potassium chlorate.
In one embodiment, prior to step a, the potassium chloride brine is further subjected to pH adjustment, temperature reduction or treatment for removing free chlorine.
In one embodiment, the nanofiltration membrane used in the first nanofiltration and/or the second nanofiltration may be selected from high molecular weight polymers such as cellulose acetate polymers, polyamides, sulfonated polysulfones, polyacrylonitrile, polyesters, polyimides, or vinyl polymers.
In one embodiment, in step a, the permeate obtained in the first nanofiltration comprises: 120-220 g/L potassium sulfate: 0.05-1 g/L of potassium chlorate, 2-20 g/L of potassium chlorate; the concentrated solution contains: 120-220 g/l of potassium chloride, 25-50g/l of potassium sulfate and 2-20 g/l of potassium chlorate; in the first nanofiltration process, the operation pressure is 0.8-3.0 MPa.
In one embodiment, in step b, the concentrate obtained in the second nanofiltration comprises: potassium chloride solution 0.01-2 g/L potassium sulfate: 25-50 g/L; in the second nanofiltration process, the operation pressure is 0.5-3.0 MPa.
In one embodiment, in step c, an MVR evaporator is used in the evaporation crystallization process.
In one embodiment, in said step c, after the evaporation process, it is necessary to add 0.1-0.3wt% NH to the crystallization mother liquor4HCO3。
In one embodiment, the penetrating fluid obtained in the first nanofiltration and/or the second nanofiltration process is used for a salt dissolving process for dissolving crude potassium chloride salt, and after suspended matters in potassium chloride brine obtained by dissolution are removed by adopting a first solid-liquid separation membrane, Na is added2CO3And NaOH, Ca in the brine2+And Mg2+The ions are converted into precipitates, and the precipitates are filtered by a second solid-liquid separation membrane and then sent into an electrolytic cell for electrolytic treatment.
In one embodiment, the first solid-liquid separation membrane is packed with hollow fiber membrane filaments.
In one embodiment, the method further comprises the step of detecting and repairing the breakage of the hollow fiber membrane filaments, and comprises the following steps:
step 1, the section of the adopted hollow fiber membrane component is rectangular, and the hollow fiber membrane is filled in the hollow fiber membrane component; the rectangle is provided with a long side and a short side;
step 2, using the plugging belt to seal one short side, so that the membrane hole of the hollow fiber membrane covered by the plugging belt is blocked, and measuring the water flux;
step 3, removing the plugging belt 16, moving the plugging belt along the long edge direction, sequentially and completely sealing other areas, and measuring the water flux after each sealing; obtaining a flux array after traversing the long side;
step 4, using the plugging belt to seal one long side, so that the membrane hole of the hollow fiber membrane covered by the plugging belt is blocked, and measuring the water flux;
step 5, removing the plugging belt, moving the plugging belt along the long edge direction, sequentially and completely sealing other areas, and measuring the water flux after each sealing; obtaining a flux array after traversing the long side;
step 6, finding out data with water flux obviously smaller than other values in the flux array after traversing the long edge, and recording the position of the long edge of the plugging band under the measuring condition corresponding to the data; finding out data with water flux obviously smaller than other values in the flux array after traversing the short edge, and recording the position of the short edge of the plugging zone under the measuring condition corresponding to the data; and taking the positions on the long edge and the short edge as coordinate values on the rectangle, and plugging the membrane holes of the hollow fiber membrane on the coordinate values by using glue.
Potassium sulfate's apparatus for producing includes:
the raw material liquid storage tank is used for storing a potassium chloride solution;
the first nanofiltration membrane is connected to the raw material liquid storage tank and is used for carrying out nanofiltration separation on raw material liquid to obtain monovalent and divalent inorganic salts;
the second nanofiltration membrane is connected to the concentrated solution side of the first nanofiltration membrane and is used for performing nanofiltration separation on monovalent and divalent inorganic salt treatment on the concentrated solution obtained from the first nanofiltration membrane;
the water feeding port is connected with the feeding port of the second nanofiltration membrane and is used for diluting the feed liquid entering the second nanofiltration membrane;
and the evaporative crystallizer is connected to the concentrated solution side of the second nanofiltration membrane and is used for carrying out evaporative crystallization treatment on the concentrated solution obtained from the second nanofiltration membrane to obtain the refined potassium sulfate.
In one embodiment, further comprising: and the salt dissolving tank is used for dissolving potassium chloride salt through permeate liquid obtained from the first nanofiltration membrane and the second nanofiltration membrane.
In one embodiment, further comprising: and the first solid-liquid separation membrane is connected to the salt dissolving tank and used for filtering the dissolved potassium chloride solution to remove suspended matters.
In one embodiment, further comprising: and a precipitation tank connected to the permeate side of the first solid-liquid separation membrane for converting calcium and magnesium ions in the permeate obtained in the first solid-liquid separation membrane 8 into a precipitate.
In one embodiment, further comprising: na (Na)2CO3An inlet and an NaOH inlet respectively connected to the precipitation tank for adding Na into the precipitation tank2CO3And NaOH.
In one embodiment, further comprising: and the second solid-liquid separation membrane is connected to the precipitation tank and used for removing the generated precipitate.
In one embodiment, further comprising: and an electrolytic cell connected to the permeation side of the second solid-liquid separation membrane for subjecting the permeate of the second solid-liquid separation membrane to electrolytic treatment.
In one embodiment, a pipeline connecting the concentrated solution side of the second nanofiltration membrane and the evaporative crystallizer is further provided with NH4HCO3And (4) adding an inlet.
Advantageous effects
The method can reuse the light salt water generated in the electrolysis process of the alkali chloride, effectively separate the potassium sulfate from the potassium chloride, and can realize the preparation of the potassium sulfate product with analytical purity grade. The main advantages of the above method include: 1. the water dilution-nanofiltration treatment is adopted, so that the deep separation of potassium sulfate and potassium chloride is realized, and the purity of the prepared potassium sulfate product is higher; 2. during the crystallization, by NH4HCO3The addition of the potassium sulfate can change the charge property of the surface of the crystal nucleus, so that the prepared potassium sulfate crystal has larger particles and higher yield; 3. the permeate liquid in the nanofiltration separation is deeply utilized again and used in the salt dissolving process of crude potassium chloride salt, so that the reutilization of byproducts is realized; 4. the filtering membrane is adopted to filter the suspended matters and the precipitate in the salt dissolving process, the purity of the refined salt water is high, and the damage of the filtering membrane is easy to detect and repair.
Drawings
FIG. 1 is a process flow diagram of the present invention;
FIG. 2 is a diagram of the apparatus of the present invention;
FIG. 3 is a diagram of a hollow fiber membrane detection process;
FIG. 4 is a diagram of a hollow fiber membrane detection process;
FIG. 5 is an SEM photograph of potassium sulfate crystals;
FIG. 6 is a graph showing a distribution of the particle size of potassium sulfate crystals.
Wherein, 1, a raw material liquid storage tank; 2. a first nanofiltration membrane; 3. a water addition port; 4. a second nanofiltration membrane; 5. an evaporative crystallizer; 6. NH (NH)4HCO3An inlet port; 7. a salt dissolving tank; 8. a first solid-liquid separation membrane; 9. a settling tank; 10. na (Na)2CO3An inlet port; 11. a NaOH inlet; 12. a second solid-liquid separation membrane; 13. an electrolytic cell; 14. a hollow fiber membrane module; 15. a hollow fiber membrane; 16. and (6) plugging the belt.
Detailed Description
The material to be treated by the invention is light salt water generated after electrolysis in a potash plant, mainly comprises potassium chloride and potassium sulfate, and mainly comprises the following main components: 120-220 g/l of potassium chloride, 3-13 g/l of potassium sulfate and 2-20 g/l of potassium chlorate. Before separation and purification, the pH value of the product is adjusted, the temperature is reduced, and free chlorine is removed.
In the steps of the invention, firstly, the potassium chloride brine is subjected to salt separation treatment by adopting a first nanofiltration membrane, and low sulfate radical salt water and sulfate radical-rich brine can be obtained because the nanofiltration membrane has higher rejection rate on divalent salt ions, wherein the low sulfate radical salt water mainly comprises the following components: 120-220 g/L potassium sulfate: 0.05-1 g/L, 2-20 g/L potassium chlorate. The sulfate-rich brine mainly comprises the following components: 120-220 g/l of potassium chloride, 25-50g/l of potassium sulfate and 2-20 g/l of potassium chlorate;
the process has the innovation point that the obtained sulfate-rich brine is enriched in potassium sulfate, and the process has the advantages that the purity of the potassium sulfate can be further improved by performing secondary nanofiltration on the sulfate-rich brine in a deionized water adding mode, so that refined potassium sulfate is obtained; if the dilution step is not used, potassium chloride is obtained in the crystallization process after direct secondary concentration and evaporation, and potassium sulfate cannot be obtained. The method comprises the following specific steps: deionized water (total water amount is about 3-8 times of the material) is added through continuous mixing, and after entering a membrane purification system, the content of the treated material is as follows: potassium chloride solution 0.01-2 g/L potassium sulfate: 25-50 g/L; the enrichment of potassium sulfate is further realized in the step, and the separation of potassium chloride is realized.
After the refined potassium sulfate saline water is obtained, the refined potassium sulfate saline water can be further concentrated by MVR evaporation, concentrated by 2.2-4.4 times, and then analytically pure potassium sulfate can be obtained by means of cooling crystallization. During the crystallization, auxiliary NH is added4HCO3The charge on the surface of crystal nucleus can be regulated to make crystal nucleus grow larger, and its added quantity can be 0.1-0.3wt% of crystallization mother liquor, and the NH can be dried by means of subsequent crystal grain drying process4CO3And the crystal can be removed easily in the subsequent crystal drying process, and the product quality is not influenced.
In the purification step and the nanofiltration membrane separation step, the brine with low sulfate radical and high potassium chloride can be obtained and sent into a low-nitrate brine storage tank, and the brine can be further used in a salt dissolving section to be recycled. Dissolving salt in water, filtering with hollow fiber membrane module to remove suspended matter, and adding Na2CO3And NaOH, Ca in the brine2+And Mg2+After the ions are converted into a precipitate,removing by a filter membrane to obtain refined potassium chloride brine, and reusing the refined potassium chloride brine in the process of ionic membrane caustic soda.
In the above steps, the hollow fiber membrane module used is mainly used for removing suspended particles in the salt solution, and in order to further prevent the damage of the whole equipment caused by the fracture in the hollow fiber membrane made of polymer material, the following detection and repair steps are adopted:
step 1, the section of the adopted hollow fiber membrane component 14 is rectangular, and a hollow fiber membrane 15 is filled in the hollow fiber membrane component; the rectangle is provided with a long side and a short side;
as shown in fig. 3: step 2, using the plugging belt 16 to seal one short side, so that the membrane hole of the hollow fiber membrane 15 covered by the plugging belt 16 is blocked, and measuring the water flux;
step 3, removing the plugging belt 16, then moving the plugging belt 16 along the long edge direction, sequentially and completely sealing other areas, and measuring the water flux after each sealing; obtaining a flux array after traversing the long side;
as shown in fig. 4: step 4, using the plugging belt 16 to seal one long side, so that the membrane hole of the hollow fiber membrane 15 covered by the plugging belt 16 is blocked, and measuring the water flux;
step 5, removing the plugging belt 16, then moving the plugging belt 16 along the long edge direction, sequentially and completely sealing other areas, and measuring the water flux after each sealing; obtaining a flux array after traversing the long side;
step 6, finding out data with water flux obviously smaller than other values in the flux array after traversing the long edge, and recording the position of the long edge of the plugging band 16 under the measuring condition corresponding to the data; finding out data with water flux obviously smaller than other values in the flux array after traversing the short edge, and recording the position of the short edge of the plugging zone 16 under the measuring condition corresponding to the data; and taking the positions on the long edge and the short edge as coordinate values on the rectangle, and plugging the membrane holes of the hollow fiber membrane on the coordinate values by using glue.
With the above-described inspection and repair means, since all the hollow fiber membranes are randomly distributed when the hollow fiber membrane module 14 is packaged, it is considered that the number of hollow fiber membranes within a predetermined area range is approximately equal. If one hollow fiber membrane is broken, the flux is obviously increased during the filtering process, and for the whole membrane module shift, which hollow fiber membrane is broken cannot be determined due to the large number of hollow fiber membranes; therefore, after a strip-shaped area is blocked by sequentially using the blocking belt along the long edge, when filtration is performed (in the filtration process, the blocking belt is positioned on the water inlet side of the hollow fiber membrane module), the hollow fiber membrane under the area no longer has a filtration function, if the just fractured hollow fiber membrane is positioned in the blocked area, the flux data under the blocking condition is obviously smaller than that under other conditions, and the numerical value has a significant difference (in other blocking conditions, the just fractured hollow fiber membrane is not in the blocking state and has the filtration function again, so that the flux of the whole hollow fiber membrane is obviously increased); therefore, a position which is obviously smaller than other numerical values in the flux array when the long side is sequentially plugged can be obtained respectively, a position which is obviously smaller than other numerical values in the flux array when the short side is sequentially plugged can also be obtained, the two positions respectively correspond to the position coordinates of the long side and the short side, the position where the coordinate values are crossed is the position where the hollow fiber membrane is broken, and then the sealant is used for blocking the pore channel of the hollow fiber membrane at the position, so that the broken hollow fiber membrane does not have water pressure any more during secondary filtration, the whole assembly is enabled to recover normal operation, and all the components are not required to be scrapped.
The integrated potassium sulfate production device adopted in the invention is shown in fig. 2 and comprises:
a raw material liquid storage tank 1 for storing a potassium chloride solution;
the first nanofiltration membrane 2 is connected to the raw material liquid storage tank 1 and is used for carrying out nanofiltration separation on raw material liquid to obtain monovalent and divalent inorganic salts;
the second nanofiltration membrane 4 is connected to the concentrated solution side of the first nanofiltration membrane 2 and is used for performing nanofiltration separation on monovalent and divalent inorganic salt treatment on the concentrated solution obtained from the first nanofiltration membrane 2;
the water inlet 3 is connected to a feed inlet of the second nanofiltration membrane 4 and is used for diluting the feed liquid entering the second nanofiltration membrane 4;
and the evaporative crystallizer 5 is connected to the concentrated solution side of the second nanofiltration membrane 4 and is used for carrying out evaporative crystallization treatment on the concentrated solution obtained from the second nanofiltration membrane 4 to obtain the refined potassium sulfate.
In one embodiment, further comprising: and the salt dissolving tank 7 is connected with the permeation sides of the first nanofiltration membrane 2 and the second nanofiltration membrane 4, and the salt dissolving tank 7 is used for dissolving potassium chloride salt by using permeate obtained from the first nanofiltration membrane 2 and the second nanofiltration membrane 4.
In one embodiment, further comprising: and the first solid-liquid separation membrane 8 is connected to the salt dissolving tank 7 and is used for filtering the dissolved potassium chloride solution to remove suspended matters.
In one embodiment, further comprising: and a precipitation tank 9 connected to the permeate side of the first solid-liquid separation membrane 8, for converting calcium and magnesium ions in the permeate obtained by the first solid-liquid separation membrane 8 into a precipitate.
In one embodiment, further comprising: na (Na)2CO3An inlet 10 and an NaOH inlet 11 respectively connected to the precipitation tank 9 for respectively adding Na into the precipitation tank 92CO3And NaOH.
In one embodiment, further comprising: and a second solid-liquid separation membrane 12 connected to the precipitation tank 9 for removing the generated precipitate.
In one embodiment, further comprising: an electrolytic cell 13 connected to the permeation side of the second solid-liquid separation membrane 12 for performing electrolytic treatment on the permeate of the second solid-liquid separation membrane 12.
In one embodiment, NH is further provided on the pipeline connecting the concentrated solution side of the second nanofiltration membrane 4 and the evaporative crystallizer 54CO3And (4) adding an inlet.
Example 1
After the pH value of the dilute brine is adjusted, dechlorination and temperature reduction are carried out after potassium chloride electrolysis, the dilute brine contains 180g/L of potassium chloride, 4.4g/L of potassium sulfate and 1.2g/L of potassium chlorate, a nanofiltration membrane is adopted to separate divalent salt (the operation pressure is 1.5 MPa), the nanofiltration membrane is made of polyamide, and a first concentrated solution and a first penetrating fluid are obtained; continuously adding 4 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.2 MPa) to obtain a second concentrated solution and a second penetrating fluid; and concentrating the second concentrated solution by adopting MVR, cooling, crystallizing, and drying crystals to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding into a salt dissolving tank containing crude potassium chloride for dissolving salt to obtain saline water, filtering with hollow fiber membrane with average pore size of 0.45um to remove suspended substances, and adding Na into penetrating fluid of hollow fiber membrane2CO3And NaOH, Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+The amount of the sodium hydroxide is 0.15g/L more, and the addition amount of NaOH is more than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.05g/L more2+And Mg2+Converting ions into precipitates, filtering the precipitates by using a ceramic microfiltration membrane with the average pore diameter of 50nm to obtain refined brine, and conveying the refined brine into an electrolytic cell for electrolytic treatment.
Example 2
After the pH value of the dilute brine is adjusted, dechlorination and temperature reduction are carried out after potassium chloride electrolysis, the dilute brine contains 160g/L of potassium chloride, 3.2g/L of potassium sulfate and 0.3g/L of potassium chlorate, a nanofiltration membrane is adopted to separate divalent salt (the operation pressure is 1.2 MPa), the nanofiltration membrane is made of polyamide, and a first concentrated solution and a first penetrating fluid are obtained; continuously adding 5 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.0 MPa) to obtain a second concentrated solution and a second penetrating fluid; and concentrating the second concentrated solution by adopting MVR, cooling, crystallizing, and drying crystals to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding into a salt dissolving tank containing crude potassium chloride for dissolving salt to obtain saline water, filtering with hollow fiber membrane with average pore size of 0.45um to remove suspended substances, and adding Na into penetrating fluid of hollow fiber membrane2CO3And NaOH，Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+In an amount of 0.20g/L more, NaOH being added in an amount larger than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.10g/L more2+And Mg2+Converting ions into precipitates, filtering the precipitates by using a ceramic microfiltration membrane with the average pore diameter of 50nm to obtain refined brine, and conveying the refined brine into an electrolytic cell for electrolytic treatment.
Example 3
After the pH value of the dilute brine is adjusted, dechlorination and temperature reduction are carried out after potassium chloride electrolysis, the dilute brine contains 140g/L of potassium chloride, 7.6g/L of potassium sulfate and 2.3g/L of potassium chlorate, a nanofiltration membrane is adopted to separate divalent salt (the operation pressure is 1.8 MPa), the nanofiltration membrane is made of polyamide, and a first concentrated solution and a first penetrating fluid are obtained; continuously adding 8 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.5 MPa) to obtain a second concentrated solution and a second penetrating fluid; and concentrating the second concentrated solution by adopting MVR, cooling, crystallizing, and drying crystals to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding into a salt dissolving tank containing crude potassium chloride for dissolving salt to obtain saline water, filtering with hollow fiber membrane with average pore size of 0.45um to remove suspended substances, and adding Na into penetrating fluid of hollow fiber membrane2CO3And NaOH, Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+In an amount of 0.05g/L more, NaOH being added in an amount larger than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.10g/L more2+And Mg2+Converting ions into precipitates, filtering the precipitates by using a ceramic microfiltration membrane with the average pore diameter of 50nm to obtain refined brine, and conveying the refined brine into an electrolytic cell for electrolytic treatment.
Example 4
The differences from example 1 are: adding 0.1-0.3wt% of NH into the concentrated saline after MVR evaporation4HCO3；
The dilute brine after the electrolysis of the potassium chloride is subjected to pH adjustment, dechlorination and temperature reduction treatment, contains 180g/L of potassium chloride, 4.4g/L of potassium sulfate and 1.2g/L of potassium chlorate, and adopts a nanofiltration membraneSeparating divalent salt (operation pressure is 1.5 MPa), wherein the nanofiltration membrane is made of polyamide to obtain a first concentrated solution and a first penetrating fluid; continuously adding 4 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.2 MPa) to obtain a second concentrated solution and a second penetrating fluid; the second concentrated solution is concentrated by MVR and then is added with 0.1 to 0.3 weight percent of NH4HCO3Cooling, crystallizing and drying the crystal to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding into a salt dissolving tank containing crude potassium chloride for dissolving salt to obtain saline water, filtering with hollow fiber membrane with average pore size of 0.45um to remove suspended substances, and adding Na into penetrating fluid of hollow fiber membrane2CO3And NaOH, Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+The amount of the sodium hydroxide is 0.15g/L more, and the addition amount of NaOH is more than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.05g/L more2+And Mg2+Converting ions into precipitates, filtering the precipitates by using a ceramic microfiltration membrane with the average pore diameter of 50nm to obtain refined brine, and conveying the refined brine into an electrolytic cell for electrolytic treatment.
Example 5
The differences from example 2 are: adding 0.1-0.3wt% of NH into the concentrated saline after MVR evaporation4HCO3；
After the pH value of the dilute brine is adjusted, dechlorination and temperature reduction are carried out after potassium chloride electrolysis, the dilute brine contains 160g/L of potassium chloride, 3.2g/L of potassium sulfate and 0.3g/L of potassium chlorate, a nanofiltration membrane is adopted to separate divalent salt (the operation pressure is 1.2 MPa), the nanofiltration membrane is made of polyamide, and a first concentrated solution and a first penetrating fluid are obtained; continuously adding 5 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.0 MPa) to obtain a second concentrated solution and a second penetrating fluid; the second concentrated solution is concentrated by MVR and then is added with 0.1 to 0.3 weight percent of NH4HCO3Cooling, crystallizing and drying the crystal to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding potassium chloride crude productDissolving salt in a salt tank to obtain saline water, filtering with hollow fiber membrane with average pore diameter of 0.45um to remove suspended substances, and adding Na into penetrating fluid of the hollow fiber membrane2CO3And NaOH, Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+In an amount of 0.20g/L more, NaOH being added in an amount larger than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.10g/L more2+And Mg2+Converting ions into precipitates, filtering the precipitates by using a ceramic microfiltration membrane with the average pore diameter of 50nm to obtain refined brine, and conveying the refined brine into an electrolytic cell for electrolytic treatment.
Example 6
The differences from example 3 are: adding 0.1-0.3wt% of NH into the concentrated saline after MVR evaporation4HCO3；
After the pH value of the dilute brine is adjusted, dechlorination and temperature reduction are carried out after potassium chloride electrolysis, the dilute brine contains 140g/L of potassium chloride, 7.6g/L of potassium sulfate and 2.3g/L of potassium chlorate, a nanofiltration membrane is adopted to separate divalent salt (the operation pressure is 1.8 MPa), the nanofiltration membrane is made of polyamide, and a first concentrated solution and a first penetrating fluid are obtained; continuously adding 8 times of deionized water into the first concentrated solution for dilution, and separating divalent salt through a second nanofiltration membrane (the operating pressure is 1.5 MPa) to obtain a second concentrated solution and a second penetrating fluid; the second concentrated solution is concentrated by MVR and then is added with 0.1 to 0.3 weight percent of NH4HCO3Cooling, crystallizing and drying the crystal to obtain analytically pure potassium sulfate.
Mixing the first penetrating fluid and the second penetrating fluid, adding into a salt dissolving tank containing crude potassium chloride for dissolving salt to obtain saline water, filtering with hollow fiber membrane with average pore size of 0.45um to remove suspended substances, and adding Na into penetrating fluid of hollow fiber membrane2CO3And NaOH, Na2CO3Is added in an amount of more than that of completely precipitating Ca in the brine2+In an amount of 0.05g/L more, NaOH being added in an amount larger than that of Mg in the completely precipitated brine2+The amount of Ca in the brine is 0.10g/L more2+And Mg2+Converting ions into precipitate, filtering with ceramic microfiltration membrane with average pore diameter of 50nm to obtain refined salt water, and feeding into electrolytic tank for electrolysisAnd (6) processing.
The operational data obtained from the above procedure are as follows:
from the comparison of the operation results of example 1 and comparative example 1 in the above table, the concentration by the first nanofiltration process is further diluted and then the second nanofiltration process is performed, thereby effectively making the pair containing KCl and K2SO4Decrease of KCl retention in the concentrate and K2SO4The rejection rate is improved, so that the separation degree of the divalent salt on the surface of the nanofiltration membrane is higher, more monovalent salt remained in the first nanofiltration concentrated solution can permeate the nanofiltration membrane, and the finally obtained K is improved2SO4The purity of (2).
In addition, the SEM photograph of the recovered potassium sulfate crystals prepared in example 4 is shown in fig. 5, and the particle size distribution of the potassium sulfate crystal grains in examples 1 and 4 is shown in fig. 6, from which it can be seen that NH was used in the crystallization process4HCO3The obtained crystal has larger grain diameter, thereby being beneficial to subsequent centrifugal separation operation and having higher yield.
Claims (10)
1. The production process of potassium sulfate is characterized by comprising the following steps of:
step a, performing first nanofiltration on potassium chloride brine to separate monovalent salt and divalent salt;
step b, diluting the concentrated solution obtained in the first nanofiltration process by adding water, and then carrying out second nanofiltration to separate monovalent salt and divalent salt;
and c, evaporating and crystallizing the concentrated solution obtained by the second nanofiltration to obtain analytically pure potassium sulfate.
2. The process for the production of potassium sulfate as claimed in claim 1, wherein in one embodiment, the dilution factor in step b is 3-8; in one embodiment, in the step a, the weak brine of potassium chloride contains 120-220 g/l of potassium chloride, 3-13 g/l of potassium sulfate and 2-20 g/l of potassium chlorate.
3. The process for the production of potassium sulfate as set forth in claim 1, wherein, in one embodiment, the potassium chloride weak brine is further subjected to pH adjustment, temperature reduction or free chlorine removal before step a.
4. The process for producing potassium sulfate according to claim 1, wherein the nanofiltration membrane used in the first nanofiltration and/or the second nanofiltration is selected from the group consisting of cellulose acetate polymers, polyamides, sulfonated polysulfones, polyacrylonitriles, polyesters, polyimides, and vinyl polymers; in one embodiment, in step a, the permeate obtained in the first nanofiltration comprises: 120-220 g/L potassium sulfate: 0.05-1 g/L of potassium chlorate, 2-20 g/L of potassium chlorate; the concentrated solution contains: 120-220 g/l of potassium chloride, 25-50g/l of potassium sulfate and 2-20 g/l of potassium chlorate; in one embodiment, in step b, the concentrate obtained in the second nanofiltration comprises: potassium chloride solution 0.01-2 g/L potassium sulfate: 25 to 50 g/L.
5. The process for the production of potassium sulfate as claimed in claim 1, wherein in one embodiment, the step c, the evaporative crystallization process is performed by using an MVR evaporator; in one embodiment, in said step c, after the evaporation process, it is necessary to add 0.1-0.3wt% NH to the crystallization mother liquor4HCO3(ii) a In one embodiment, the penetrating fluid obtained in the first nanofiltration and/or the second nanofiltration process is used for a salt dissolving process for dissolving crude potassium chloride salt, and after suspended matters in potassium chloride brine obtained by dissolution are removed by adopting a first solid-liquid separation membrane, Na is added2CO3And NaOH, Ca in the brine2+And Mg2+The ions are converted into precipitates, and the precipitates are filtered by a second solid-liquid separation membrane and then sent into an electrolytic cell for electrolytic treatment.
6. The process for the production of potassium sulfate according to claim 1, wherein in one embodiment, the first solid-liquid separation membrane is packed with hollow fiber membrane filaments; in one embodiment, the method further comprises the step of detecting and repairing the breakage of the hollow fiber membrane filaments, and comprises the following steps: step 1, the section of a hollow fiber membrane component (14) is rectangular, and a hollow fiber membrane (15) is filled in the hollow fiber membrane component; the rectangle is provided with a long side and a short side; step 2, using a plugging belt (16) to seal a short side so as to block the membrane pores of the hollow fiber membrane 15 covered by the plugging belt (16) and measure the water flux, step 3, removing the plugging belt (16), moving the plugging belt (16) along the long side direction, sequentially sealing other areas, measuring the water flux after each sealing, obtaining a flux array traversing the long side, step 4, using the plugging belt (16) to seal a long side so as to block the membrane pores of the hollow fiber membrane (15) covered by the plugging belt (16) and measure the water flux, step 5, removing the plugging belt (16), moving the plugging belt (16) along the long side direction, sequentially sealing other areas, measuring the water flux after each sealing, obtaining the flux array traversing the long side, step 6, finding out data of which the water flux is obviously smaller than other values in the flux array after traversing the long edge, and recording the position of the long edge of the plugging band (16) under the measuring condition corresponding to the data; then finding out data with water flux obviously smaller than other values in the flux array after traversing the short edge, and recording the position of the short edge of the plugging band (16) under the measuring condition corresponding to the data; and taking the positions on the long edge and the short edge as coordinate values on the rectangle, and plugging the membrane holes of the hollow fiber membrane on the coordinate values by using glue.
7. The potassium sulfate production device is characterized by comprising:
the raw material liquid storage tank (1) is used for storing a potassium chloride solution;
the first nanofiltration membrane (2) is connected to the raw material liquid storage tank (1) and is used for carrying out nanofiltration separation on raw material liquid to obtain monovalent and divalent inorganic salts;
the second nanofiltration membrane (4) is connected to the concentrated solution side of the first nanofiltration membrane (2) and is used for performing nanofiltration separation on monovalent and divalent inorganic salt treatment on the concentrated solution obtained from the first nanofiltration membrane (2);
the water adding port (3) is connected with a feed port of the second nanofiltration membrane (4) and is used for diluting feed liquid entering the second nanofiltration membrane (4);
and the evaporative crystallizer (5) is connected to the concentrated solution side of the second nanofiltration membrane (4) and is used for carrying out evaporative crystallization treatment on the concentrated solution obtained in the second nanofiltration membrane (4) to obtain the refined potassium sulfate.
8. The apparatus for the production of potassium sulfate as set forth in claim 7, further comprising, in one embodiment: the salt dissolving tank (7) is connected with the permeation sides of the first nanofiltration membrane (2) and the second nanofiltration membrane (4), and the salt dissolving tank (7) is used for dissolving potassium chloride salt through permeation liquid obtained from the first nanofiltration membrane (2) and the second nanofiltration membrane (4); in one embodiment, further comprising: the first solid-liquid separation membrane (8) is connected to the salt dissolving tank (7) and is used for filtering the dissolved potassium chloride solution to remove suspended matters; in one embodiment, further comprising: a precipitation tank (9) connected to the permeate side of the first solid-liquid separation membrane (8) and used for converting calcium and magnesium ions in the permeate obtained in the first solid-liquid separation membrane (8) into precipitates; in one embodiment, further comprising: na (Na)2CO3An inlet 10 and an NaOH inlet 11 respectively connected to the precipitation tank 9 for adding Na into the precipitation tank 92CO3And NaOH.
9. The apparatus for the production of potassium sulfate as set forth in claim 7, further comprising, in one embodiment: and a second solid-liquid separation membrane (12) connected to the precipitation tank (9) and used for removing the generated precipitate.
10. According to the claimsThe apparatus for producing potassium sulfate according to claim 7, further comprising, in one embodiment: an electrolytic cell (13) connected to the permeation side of the second solid-liquid separation membrane (12) and configured to perform electrolytic treatment on the permeate of the second solid-liquid separation membrane (12); in one embodiment, NH is further arranged on a pipeline connected with the evaporative crystallizer (5) at the concentrated solution side of the second nanofiltration membrane (4)4HCO3And (4) adding an inlet.
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