High-efficiency salt production process by saturated brine feeding into tank MVR

Abstract

The application discloses a saturated brine tank-in MVR efficient salt making process and belongs to the technical field of brine salt making. The process comprises the following steps: pretreatment, preparation of refined brine, MVR evaporation crystallization, seed circulation step, cold separation crystallization step, potassium salt separation step, and collection of magnesium chloride enrichment liquid. The preparation of refined brine step is as follows: after crude brine is preheated by a preheating system, the temperature of the crude brine is increased to 50-60 DEG C, sodium citrate is added to the crude brine, after stirring and mixing for 8-10 min, sodium carbonate is added, and the stirring is continued for 35-40 min, and then solid-liquid separation is carried out to obtain calcium carbonate and refined brine. In the absence of a scale inhibitor, the equipment and pipeline structure phenomenon is reduced, the raw material utilization rate in the brine is improved, and the multi-stage utilization of heat energy is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of brine salt production, specifically involving a high-efficiency MVR salt production process using saturated brine in a tank. Background Technology

[0002] Salt (sodium chloride), as an important chemical raw material and daily necessity, has long relied on the traditional process of raw salt leaching, purification, evaporation, and crystallization. Traditional brine salt production processes often employ multi-effect evaporation (MED) technology, which utilizes steam heat energy through multiple evaporators connected in series. However, this technology suffers from problems such as high equipment investment, high steam consumption, and persistently high operating costs. With the maturation of mechanical vapor recompression (MVR) technology, its application in the salt production field is gradually being promoted. MVR technology compresses and heats secondary steam using a compressor, reusing it as a heat source for the evaporator, significantly reducing fresh steam consumption. However, technical bottlenecks such as equipment scaling, impurity ion enrichment, and low resource utilization during brine evaporation still constrain the further development of this technology.

[0003] In the brine pretreatment stage, calcium ion removal is crucial for ensuring the stable operation of the evaporation system. Traditional processes typically employ direct sodium carbonate precipitation, but the resulting calcium carbonate precipitate easily forms scale on equipment surfaces. Especially under high-temperature evaporation conditions, the rapid formation of calcite-type calcium carbonate exacerbates scaling on the heating pipe walls, leading to decreased heat transfer efficiency and increased maintenance costs. Furthermore, impurities such as sulfate and magnesium ions in the brine gradually accumulate during evaporation. If the resulting bittern mother liquor is not effectively treated, it not only wastes resources but also poses environmental disposal challenges.

[0004] In existing technologies, the comprehensive utilization of bittern mainly focuses on the extraction of potassium and magnesium salts, but traditional processes suffer from low separation efficiency and insufficient product purity. Sodium sulfate crystallization separation typically employs hot-melt or salting-out methods, but these are energy-intensive. Potassium chloride extraction often relies on low-temperature crystallization, but excessively high magnesium ion concentrations in the mother liquor can lead to eutectic phenomena, affecting product yield. Achieving efficient separation and high-value utilization of sodium, potassium, and magnesium resources remains a key technological challenge for the industry.

[0005] In recent years, with breakthroughs in membrane separation technology and crystallization kinetics control, brine refining and resource utilization technologies have made some progress. However, existing processes still have the following shortcomings: the lack of crystal form control technology during calcium ion precipitation makes it difficult to fundamentally solve the scaling problem; scale-forming ions in the evaporation crystallization system are prone to precipitate on the heat exchange surface; the separation efficiency of multiple components in bittern mother liquor is low, and the recovery rate of potassium and magnesium resources is limited; the integration of process thermal energy is insufficient, and the sensible heat of high-temperature mother liquor is not fully recovered and utilized.

[0006] Therefore, developing a brine salt production process that combines high efficiency and energy saving, scale prevention and inhibition, and comprehensive resource utilization is of great significance for promoting technological upgrading in the salt production industry and realizing the cascade utilization of salt, alkali, potassium, and magnesium resources. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a high-efficiency MVR salt production process for saturated brine entering a tank. This process reduces equipment and pipeline structural issues without the use of scale inhibitors, improves the utilization rate of raw materials in the brine, and achieves multi-stage utilization of thermal energy.

[0008] To solve the above technical problems, the technical solution adopted by the present invention is as follows: a high-efficiency salt production process for saturated brine entering a tank using MVR, comprising the following steps: pretreatment, preparation of refined brine, MVR evaporation and crystallization, seed crystal circulation step, cold precipitation crystallization step, potassium salt separation step, and collection of magnesium chloride enrichment solution; A method for efficient salt production and co-production of potassium and magnesium resources from saturated brine using MVR (Mechanical Vapor Regeneration) includes the following steps: (a) Pretreatment: Saturated brine is pretreated by air flotation to remove impurities, pH adjustment, clarification and filtration to obtain crude brine; (b) Preparation of refined brine: After the crude brine is preheated by the preheating system, the temperature is raised to 50-60℃, sodium citrate is added to it, and after stirring and mixing for 8-10 minutes, sodium carbonate is added and stirring is continued for 35-40 minutes. Solid-liquid separation is performed to obtain calcium carbonate and refined brine. (c) MVR evaporation crystallization: The refined brine is fed into the MVR evaporation crystallization system to evaporate and precipitate sodium chloride crystals. After thickening, centrifugation and drying, the finished salt is obtained. The secondary steam generated in the MVR evaporation crystallization system is compressed by a steam compressor and reused as a heat source. (d) Seed crystal recycling step: The 3-5wt% sodium chloride slurry generated in the MVR evaporation crystallization system is continuously refluxed and mixed with the refined brine obtained in step (b), and then fed into the MVR evaporation crystallization system together; (e) Cold crystallization step: The bitter mother liquor discharged from the MVR evaporation crystallization system is first sent to the flash evaporation system to recover its heat energy. The cooled mother liquor is then sent to the cold crystallizer, where hexadecyltrimethylammonium bromide is added to inhibit the formation of eutectic. Sodium sulfate decahydrate crystals are precipitated by temperature control and cooling. Sodium sulfate decahydrate product is obtained by solid-liquid separation. (f) Potassium salt separation step: The mother liquor after separating sodium sulfate decahydrate in step (e) is further concentrated and cooled to 15-25℃ to precipitate potassium chloride crystals. The potassium chloride product is obtained by solid-liquid separation. (g) Collect magnesium chloride enrichment solution: The final mother liquor after separating potassium chloride in step (f) is discharged and collected as high-purity magnesium chloride enrichment solution.

[0009] The air flotation impurity removal in step (a) involves transporting the saturated brine from the salt field to the air flotation system. Under the action of compressed air, the suspended insoluble matter and a small amount of organic matter in the brine float to the liquid surface and are scraped off by the air flotation system scraper. The pH adjustment mentioned in step (a) is as follows: after air flotation to remove impurities, the saturated brine is transported to a pH adjustment device and the pH value is adjusted to 8.3-8.6. The clarification and filtration pretreatment described in step (a) involves clarifying and filtering the saturated brine after pH adjustment, then filtering the filtered liquid into the evaporator preheating system, and removing the mud-containing material at the bottom by pressure filtration.

[0010] The amount of sodium citrate added in step (b) is 0.8-1 times the molar content of calcium ions in the crude brine; The amount of sodium carbonate added in step (b) is 1.05-1.1 times the molar content of calcium ions in the crude brine.

[0011] The refluxed sodium chloride slurry in step (d) has a solid content of 10-15% and a grain size of 20-80 μm; The flash evaporation system described in step (e) is a two-stage flash evaporation system, which uses the secondary steam generated by flash evaporation of bittern mother liquor as the heat source for the preheating system. The two-stage flash evaporation system described in step (e) raises the steam temperature by 6-8°C in the first stage and by 18-20°C in the second stage. After flash evaporation, the temperature of the mother liquor drops below 50°C in step (e), and the discharged condensate is used to preheat the feed brine to further recover heat. The amount of hexadecyltrimethylammonium bromide added in step (e) is 0.2-0.5 g / L; The cooling rate described in step (e) is specifically as follows: the temperature is reduced to 9-11℃ at a rate of 1.4-1.6℃ / h to precipitate most of Na2SO4·10H2O, and then reduced to 4-5℃ at a rate of 0.8-1℃ / h and kept at a constant temperature for 3-4 hours to ensure complete precipitation of sodium sulfate.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the step of preparing refined brine in this invention, the added sodium citrate preferentially captures free Ca. 2+ This forms a stable water-soluble complex. Adding sodium carbonate causes the citrate ion and calcium ion complex to slowly release Ca2+. 2+ With CO3 2- The calcium carbonate precipitate generated by this method is not prone to forming hard scale on the equipment. This may be because citrate ions adsorbed on the surface of calcium carbonate crystals inhibit the growth of calcite-type calcium carbonate, which is prone to forming hard scale, and induce the formation of looser calcium carbonate crystals.

[0013] (2) The present invention has a seed crystal circulation step. By refluxing the salt slurry containing a large number of fine crystals from the system, sufficient sodium chloride crystallization nuclei are provided for the brine entering the evaporator. The rapid crystallization of sodium chloride makes it difficult for dissolved scale-forming components to crystallize, effectively inhibiting scale formation on the tank wall and heating pipe wall.

[0014] (3) This invention converts sulfate, potassium and magnesium elements in bittern into three valuable products: sodium sulfate, potassium chloride and magnesium chloride enrichment solution, respectively, thereby significantly improving economic benefits.

[0015] (4) The two-stage flash evaporation system in this invention fully recovers the sensible heat of the high-temperature bitter mother liquor and converts it into valuable low-grade steam for preheating raw materials, which greatly reduces the consumption of live steam. Cold crystallization is carried out at a temperature close to ambient temperature, with extremely low energy consumption.

[0016] (5) The finished salt obtained by the process method of the present invention has a purity of 99.5-99.6% and the sodium sulfate decahydrate has a purity of 92.0-93.1%. Detailed Implementation

[0017] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0018] Example 1 The process of this invention is used to treat saturated brine from salt fields. The composition of the saturated brine is: Na + 135g / L, K + 3.6 g / L, Mg 2 + 13.4 g / L, Ca 2+ 2.5 g / L, Cl - 238g / L, SO4 2- 28g / L.

[0019] Saturated brine with a flow rate of 100 L / h is subjected to air flotation, pH adjustment to 8.3, clarification, pressure filtration, and precision filtration to obtain crude brine.

[0020] 2. The crude brine is preheated to 55℃, and sodium citrate is added according to the calcium ion concentration, with a molar amount of Ca. 2+ Add sodium carbonate at a concentration of 0.8 times the volume of Ca, stir for 8 minutes, and then add the sodium carbonate. The molar amount of Ca is... 2+ Add 1.05 times the amount of the original amount, stir for 35 minutes, filter after reaction to obtain refined brine.

[0021] 3. The refined brine is fed into the MVR system. At the same time, 3 wt% salt slurry with a solid content of 15% and a crystal size of 20-80 μm is refluxed and mixed with the refined brine; sodium chloride crystals are evaporated and precipitated, and the product salt is obtained after thickening, centrifugation, and drying.

[0022] 4. The high-temperature mother liquor taken from the system undergoes a first-stage flash evaporation to raise the steam temperature by 6°C, followed by a second-stage flash evaporation to raise the steam temperature by 20°C. After recovering heat through these two flash evaporations, the temperature is lowered to 48°C. It then enters a cold crystallizer, where the temperature is first lowered to 11°C at a rate of 1.4°C / h, then further lowered to 5°C at a rate of 0.8°C / h and held at this temperature for 4 hours. 0.2 g / L hexadecyltrimethylammonium bromide is added to inhibit eutectic formation, precipitating sodium sulfate decahydrate, and the product is obtained. The remaining mother liquor is concentrated and cooled to 20°C, precipitating potassium chloride. The final mother liquor is a solution rich in MgCl2, with a MgCl2 concentration of 283 g / L.

[0023] The purity of the finished salt obtained in this embodiment is 99.6%, and the purity of sodium sulfate decahydrate is 92.4%. 1 ton of saturated brine yields 206 kg of finished salt and 24.7 kg of sodium sulfate decahydrate.

[0024] Example 2 The process of this invention is used to treat saturated brine from salt fields. The composition of the saturated brine is: Na + 135g / L, K + 3.6 g / L, Mg 2 + 13.4 g / L, Ca 2+ 2.5 g / L, Cl - 238g / L, SO4 2- 28g / L.

[0025] Saturated brine with a flow rate of 1.95 L / h is subjected to air flotation, pH adjustment to 8.5, clarification, pressure filtration, and precision filtration to obtain crude brine.

[0026] 2. The crude brine is preheated to 58℃. Sodium citrate is added according to the calcium ion concentration, with a molar amount of Ca. 2+ Add sodium carbonate at a concentration of 0.9 times the volume of Ca, stir for 9 minutes, and then add the sodium carbonate. The molar amount of Ca is... 2+ Add 1.08 times the amount of the original amount, stir for 38 minutes, filter after reaction to obtain refined brine.

[0027] 3. The refined brine is fed into the MVR system. At the same time, 4 wt% salt slurry with a solid content of 12% and a crystal size of 20-80 μm is refluxed and mixed with the refined brine; sodium chloride crystals are evaporated and precipitated, and the product salt is obtained after thickening, centrifugation, and drying.

[0028] 4. The high-temperature mother liquor taken from the system undergoes a first-stage flash evaporation to raise the steam temperature by 7°C, followed by a second-stage flash evaporation to raise the steam temperature by 19°C. After recovering heat energy through these two flash evaporations, the temperature is cooled to 49°C. It then enters a cold crystallizer, where the temperature is first lowered to 10°C at a rate of 1.5°C / h, then further lowered to 4.5°C at a rate of 0.9°C / h and held at this temperature for 3.5 hours. 0.3 g / L hexadecyltrimethylammonium bromide is added to inhibit eutectic formation, precipitating sodium sulfate decahydrate, which is then separated to obtain the product. The remaining mother liquor is concentrated and cooled to 19°C, precipitating potassium chloride. The final mother liquor is a solution rich in MgCl2, with a MgCl2 concentration of 277 g / L.

[0029] The purity of the finished salt obtained in this embodiment is 99.6%, and the purity of sodium sulfate decahydrate is 93.1%. 1 ton of saturated brine yields 210 kg of finished salt and 25.3 kg of sodium sulfate decahydrate.

[0030] After running continuously for 6 weeks according to the embodiment, no obvious scaling phenomenon was found on the inner walls of the equipment and pipes of the mixer and MVR evaporation system for preparing refined brine. After 8 weeks of operation, the yield of finished salt per ton of saturated brine was 96% of the initial yield per ton of saturated brine, with a small decrease.

[0031] Example 3 The process of this invention is used to treat saturated brine from salt fields. The composition of the saturated brine is: Na + 135g / L, K + 3.6 g / L, Mg 2 + 13.4 g / L, Ca 2+ 2.5 g / L, Cl - 238g / L, SO4 2- 28g / L.

[0032] Saturated brine with a flow rate of 1.90 L / h is subjected to air flotation, pH adjustment to 8.6, clarification, pressure filtration, and precision filtration to obtain crude brine.

[0033] 2. The crude brine is preheated to 60℃, and sodium citrate is added according to the calcium ion concentration, with a molar amount of Ca. 2+ Add sodium carbonate at a concentration of 1 times the volume of Ca, stir for 10 minutes, and then add sodium carbonate in a molar quantity of Ca. 2+ Add 1.1 times the amount of the liquid, stir for 40 minutes, filter after reaction to obtain refined brine.

[0034] 3. The refined brine is fed into the MVR system. At the same time, 5 wt% salt slurry with a solid content of 10% and a crystal size of 20-80 μm is refluxed and mixed with the refined brine; sodium chloride crystals are evaporated and precipitated, and the product salt is obtained after thickening, centrifugation, and drying.

[0035] 4. The high-temperature mother liquor taken from the system undergoes a first-stage flash evaporation to raise the steam temperature by 8°C, followed by a second-stage flash evaporation to raise the steam temperature by 18°C. After recovering heat energy through these two flash evaporations, the temperature is cooled to 48°C. It then enters a cold crystallizer, where the temperature is first lowered to 9°C at a rate of 1.6°C / h, then further lowered to 4°C at a rate of 1°C / h and held at this temperature for 3 hours. 0.5 g / L hexadecyltrimethylammonium bromide is added to inhibit eutectic formation, precipitating sodium sulfate decahydrate, which is then separated to obtain the product. The remaining mother liquor is concentrated and cooled to 18°C, precipitating potassium chloride. The final mother liquor is a solution rich in MgCl2, with a MgCl2 concentration of 274 g / L.

[0036] The purity of the finished salt obtained in this embodiment is 99.5%, and the purity of the sodium sulfate decahydrate is 92.0%. 1 ton of saturated brine yields 203 kg of finished salt and 24.2 kg of sodium sulfate decahydrate.

[0037] Example 4 The process of this invention is used to treat saturated brine from salt fields. The composition of the saturated brine is: Na + 135g / L, K + 3.6 g / L, Mg 2 + 13.4 g / L, Ca 2+ 2.5 g / L, Cl - 238g / L, SO4 2- 28g / L.

[0038] Saturated brine with a flow rate of 1.95 L / h is subjected to air flotation, pH adjustment to 8.5, clarification, pressure filtration, and precision filtration to obtain crude brine.

[0039] 2. The crude brine is preheated to 55℃, and sodium carbonate is added according to the calcium ion concentration, with a molar amount of Ca. 2+ Add 1.05 times the amount of the original amount, stir for 38 minutes, filter after reaction to obtain refined brine.

[0040] 3. The refined brine is fed into the MVR system. At the same time, 4 wt% salt slurry with a solid content of 12% and a crystal size of 20-80 μm is refluxed and mixed with the refined brine; sodium chloride crystals are evaporated and precipitated, and the product salt is obtained after thickening, centrifugation, and drying.

[0041] 4. The high-temperature mother liquor taken from the system undergoes a first-stage flash evaporation to raise the steam temperature by 7°C, followed by a second-stage flash evaporation to raise the steam temperature by 19°C. After recovering heat energy through these two flash evaporations, the temperature is cooled to 49°C. It then enters a cold crystallizer, where the temperature is first lowered to 10°C at a rate of 1.5°C / h, then further lowered to 4.5°C at a rate of 0.9°C / h and held at this temperature for 3.5 hours. 0.3 g / L hexadecyltrimethylammonium bromide is added to inhibit eutectic formation, precipitating sodium sulfate decahydrate, which is then separated to obtain the product. The remaining mother liquor is concentrated and cooled to 19°C, precipitating potassium chloride. The final mother liquor is a solution rich in MgCl2, with a MgCl2 concentration of 277 g / L.

[0042] The purity of the finished salt obtained in this embodiment is 99.3%, and the purity of sodium sulfate decahydrate is 93.4%. 1 ton of saturated brine yields 215 kg of finished salt and 24.7 kg of sodium sulfate decahydrate.

[0043] After running continuously for 2 weeks according to the embodiment, obvious scaling began to appear on the inner walls of the equipment and pipes of the mixer and MVR evaporation system for preparing refined brine. After running for 3 weeks, the yield of finished salt dropped significantly, down to 83% of the initial yield per ton of saturated brine.

[0044] The difference between this embodiment and Embodiment 2 is that the addition of sodium citrate is omitted; everything else is the same. The purity of the prepared salt is not significantly different, but it is prone to scaling in equipment and pipelines, especially noticeable in the mixer used for preparing refined brine. This is because the addition of sodium carbonate reduces the calcium content of the brine. 2+ With CO3 2- The rapid combination causes the CaCO3 in the solution to instantly reach extremely high supersaturation, leading to the spontaneous and abundant formation of extremely fine crystal nuclei. These microcrystals possess enormous surface energy and are highly unstable, exhibiting a strong tendency to precipitate, adhere, and grow on any accessible surface to reduce system energy. The walls of the mixer, the agitator, and subsequent pipes and pump casings become ideal deposition sites, resulting in a hardened scale layer.

[0045] Example 5 The process of this invention is used to treat saturated brine from salt fields. The composition of the saturated brine is: Na + 135g / L, K + 3.6 g / L, Mg 2 + 13.4 g / L, Ca 2+ 2.5 g / L, Cl - 238g / L, SO4 2- 28g / L.

[0046] Saturated brine with a flow rate of 1.95 L / h is subjected to air flotation, pH adjustment to 8.5, clarification, pressure filtration, and precision filtration to obtain crude brine.

[0047] 2. The crude brine is preheated to 58℃. Sodium citrate is added according to the calcium ion concentration, with a molar amount of Ca. 2+ Add sodium carbonate at a concentration of 0.9 times the volume of Ca, stir for 9 minutes, and then add the sodium carbonate. The molar amount of Ca is... 2+ Add 1.08 times the amount of the original amount, stir for 38 minutes, filter after reaction to obtain refined brine.

[0048] 3. The refined brine is fed into the MVR system. The salt slurry has a solid content of 12%, eliminating the need for salt slurry reflux and mixing with the refined brine; sodium chloride crystals are evaporated and precipitated, and then thickened, centrifuged, and dried to obtain the finished salt.

[0049] 4. The high-temperature mother liquor taken from the system undergoes a first-stage flash evaporation to raise the steam temperature by 7°C, followed by a second-stage flash evaporation to raise the steam temperature by 19°C. After recovering heat energy through these two flash evaporations, the temperature is cooled to 49°C. It then enters a cold crystallizer, where the temperature is first lowered to 10°C at a rate of 1.5°C / h, then further lowered to 4.5°C at a rate of 0.9°C / h and held at this temperature for 3.5 hours. 0.3 g / L hexadecyltrimethylammonium bromide is added to inhibit eutectic formation, precipitating sodium sulfate decahydrate, which is then separated to obtain the product. The remaining mother liquor is concentrated and cooled to 19°C, precipitating potassium chloride. The final mother liquor is a solution rich in MgCl2, with a MgCl2 concentration of 277 g / L.

[0050] The purity of the finished salt obtained in this embodiment is 98.6%, and the purity of sodium sulfate decahydrate is 92.5%. 1 ton of saturated brine yields 185 kg of finished salt and 23.7 kg of sodium sulfate decahydrate.

[0051] After running continuously for 4 weeks according to the embodiment, obvious scaling began to appear on the inner walls of the equipment and pipes of the MVR evaporation system, and the yield of finished salt dropped to 90% of the initial yield per ton of saturated brine.

[0052] Unless otherwise specified, all percentages mentioned in this application are percentages by mass.

[0053] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-efficiency salt production process using saturated brine-in-tank MVR, characterized in that, The salt production process includes the following steps: pretreatment, preparation of refined brine, MVR evaporation and crystallization, seed crystal circulation step, cold precipitation crystallization step, potassium salt separation step, and collection of magnesium chloride enrichment solution. Specifically, the following steps are included: (a) Pretreatment: Saturated brine is pretreated by air flotation to remove impurities, pH adjustment, clarification and filtration to obtain crude brine; (b) Preparation of refined brine: After the crude brine is preheated by the preheating system, the temperature is raised to 50-60℃, sodium citrate is added to it, and after stirring and mixing for 8-10 minutes, sodium carbonate is added and stirring is continued for 35-40 minutes. Solid-liquid separation is performed to obtain calcium carbonate and refined brine. (c) MVR evaporation crystallization: The refined brine is fed into the MVR evaporation crystallization system to evaporate and precipitate sodium chloride crystals. After thickening, centrifugation and drying, the finished salt is obtained. (d) Seed crystal recycling step: The 3-5wt% sodium chloride slurry generated in the MVR evaporation crystallization system is continuously refluxed and mixed with the refined brine obtained in step (b), and then fed into the MVR evaporation crystallization system together; (e) Cold crystallization step: The bitter mother liquor discharged from the MVR evaporation crystallization system is first sent to the flash evaporation system to recover its heat energy. The cooled mother liquor is then sent to the cold crystallizer, where hexadecyltrimethylammonium bromide is added to inhibit the formation of eutectic. Sodium sulfate decahydrate crystals are precipitated by temperature control and cooling. Sodium sulfate decahydrate product is obtained by solid-liquid separation. (f) Potassium salt separation step: The mother liquor after separating sodium sulfate decahydrate in step (e) is further concentrated and cooled to 15-25℃ to precipitate potassium chloride crystals. The potassium chloride product is obtained by solid-liquid separation. (g) The final mother liquor after separating potassium chloride in step (f) is discharged and collected as a high-purity magnesium chloride enrichment solution.

2. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 1, characterized in that, The pH adjustment mentioned in step (a) is as follows: after air flotation to remove impurities, the saturated brine is transported to a pH adjustment device and the pH value is adjusted to 8.3-8.

6.

3. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 1, characterized in that, In step (b), the amount of sodium citrate added is 0.8-1 times the molar content of calcium ions in the crude brine, and the amount of sodium carbonate added is 1.05-1.1 times the molar content of calcium ions in the crude brine.

4. The high-efficiency salt production process of saturated brine entering the tank MVR as described in claim 3, characterized in that, The refluxed sodium chloride slurry in step (d) has a solid content of 10-15% and a grain size of 20-80 μm.

5. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 1, characterized in that, The secondary steam generated in the MVR evaporation crystallization system described in step (c) is compressed by a steam compressor and reused as a heat source.

6. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 1, characterized in that, The flash evaporation system described in step (e) is a two-stage flash evaporation system, which uses the secondary steam generated by flash evaporation of bittern mother liquor as the heat source for the preheating system.

7. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 6, characterized in that, The two-stage flash evaporation system described in step (e) raises the steam temperature by 6-8°C in the first stage and by 18-20°C in the second stage.

8. The high-efficiency salt production process of MVR with saturated brine in a tank according to claim 1, characterized in that, The cooling rate described in step (e) is specifically as follows: the temperature is reduced to 9-11℃ at a rate of 1.4-1.6℃ / h to precipitate most of Na2SO4·10H2O, and then reduced to 4-5℃ at a rate of 0.8-1℃ / h and held at that temperature for 3-4 hours.