MVR (Mechanical Vapor Recompression) and salting-out process nitrate separation system and method thereof

Abstract

The invention discloses an MVR (Mechanical Vapor Recompression) and salting-out process nitrate separation system and a salting-out process nitrate separation method, and aims to solve the problem of low main content of a nitrate product caused by unstable salt adding amount and easiness in pipeline blockage in the conventional salting-out process nitrate separation process. The system comprises an MVR evaporation system, a flash tank, a saltpeter tank, a salt leaching system, a mixed liquid barrel, a salting pipeline and a plurality of connecting pipelines, a salt adding pipeline is additionally arranged between a first-stage salt leaching device and a mixed liquid barrel, a flowmeter and an electric control valve are sequentially arranged on the salt adding pipeline, and the flowmeter and the electric control valve are electrically connected with a central control system; by modifying the existing design, fine-particle salt slurry is stably and quantitatively added into the saltpeter tank, and the salting-out reaction condition in the saltpeter tank is optimal, so that a high-purity sodium sulfate product is continuously produced, and the quality of the saltpeter product is remarkably improved; salt slurry discharged from the salt leaching device is washed fine salt, the dissolution speed of the salt slurry in the saltpeter tank is higher, the saltpeter redissolution efficiency is higher, and saltpeter improvement is promoted.

Description

Technical Field

[0001] This application relates to the field of salt production technology, specifically to an MVR and salt precipitation nitrate removal system and method thereof. Background Technology

[0002] Currently, production lines in China using the "salting-out process" for nitrate precipitation generally suffer from low purity of the byproduct sodium sulfate. Theoretically, the main content (Na₂SO₄) of the nitrate product (sodium sulfate) is approximately 80-85%, but in actual production, it is often only around 80%. According to the national standard (GB / T 6009-2014), the main content requirement for Class III qualified anhydrous sodium sulfate is ≥92.0%. The 80% purity sodium sulfate produced by the existing process is considered substandard, has low market value, and severely impacts the economic benefits of enterprises.

[0003] For the traditional salting-out process of nitrate removal, please refer to [link / reference]. Figure 1 The system includes an MVR evaporation system, a flash evaporation tank, a nitrate tank, a salt washing system, a mixing tank, and several connecting pipes. The inventors discovered that the main reason for the low nitrate quality is the instability of the salt addition process during nitrate precipitation. Specifically, the original evaporator's salt discharge pump divides the high-concentration salt slurry produced by the MVR evaporation system into two routes: one goes to the flash evaporation tank to produce the main product salt, and the other goes to the nitrate tank for salting out nitrate. This solution has the following inherent drawbacks:

[0004] 1. Large fluctuations in salt addition and poor process stability: Because the nitrification tank is relatively large and the salt slurry is divided into two streams during the salt addition process, the same pump needs to take into account the transportation needs of two different process points (flash evaporation tank and nitrification tank), and the flow distribution is difficult to control precisely. This results in the amount of salt entering the nitrification tank being sometimes more and sometimes less, making the nitrification process very unstable and unable to meet the constant requirements of the salt precipitation method.

[0005] 2. Frequent pipe blockage: The nitrate tank maintains a certain operating pressure (positive pressure), which creates a pressure difference with the salt addition pipeline. This pressure difference can easily cause the liquid in the nitrate tank to be back-pressed into the salt addition pipeline. The back-pressed liquid mixes with the high-concentration salt slurry in the pipeline and crystallizes rapidly, causing severe blockage of the pipeline. Frequent treatment is required, which affects continuous production.

[0006] 3. Large salt slurry particles and poor solubility: The salt slurry particles produced by the MVR evaporation system have large particle sizes and small specific surface areas, resulting in low dissolution rates and low efficiency of sodium sulfate re-dissolution in the nitrate tank, which directly affects the salting-out effect.

[0007] 4. Inability to precisely control: The salting operation is in a "rough" state and cannot be precisely adjusted according to the real-time operating conditions in the nitrate tank.

[0008] In addition, in the above process, the liquid discharged from the nitrification tank is used to cool the salt slurry in the salt leg washing pipe. However, since the operating temperature of the nitrification tank is as high as 100°C, it cannot be effectively cooled. Therefore, the salt slurry and mother liquor produced by the MVR evaporation system can only be collected in the flash evaporation tank for cooling. Although the flash evaporation tank has a certain cooling capacity, it bears a heat and material volume far exceeding its design load, which causes the salt discharge pump to trip frequently and the system cannot operate continuously and stably. Summary of the Invention

[0009] Therefore, this application provides an MVR and salting-out nitrate precipitation system and method to solve the problem of low main content of nitrate product (sodium sulfate) in the existing salting-out nitrate precipitation process due to unstable salt addition and easy pipe blockage.

[0010] To achieve the above objectives, this application provides the following technical solution:

[0011] In a first aspect, an MVR and salting-out nitrate precipitation system includes: an MVR evaporation system, a flash evaporation tank, a nitrate tank, a salt washing system, a mixing tank, a salt adding pipeline, and several connecting pipelines.

[0012] The salt washing system includes a primary salt washer, a secondary salt washer, and a tertiary salt washer connected in sequence. The first and second inlets of the tertiary salt washer are connected to refined brine and salt slurry, respectively, and the outlet of the tertiary salt washer is connected to a centrifuge. The first and second outlets of the primary salt washer are connected to the first inlet of the secondary salt washer and the first inlet of the mixing tank, respectively. The third outlet of the primary salt washer is connected to the second inlet of the mixing tank through the salt addition pipe. The third inlet of the mixing tank is connected to the outlet of the flash evaporation tank. The first inlet of the primary salt washer is connected to the first outlet of the MVR evaporation system, and the second outlet of the MVR evaporation system is connected to the inlet of the flash evaporation tank. The inlet of the nitrate tank is connected to the outlet of the mixing tank, and the outlet of the nitrate tank is connected to the inlet of the MVR evaporation system.

[0013] A flow meter and an electric regulating valve are sequentially installed on the salt addition pipeline, and both the flow meter and the electric regulating valve are electrically connected to the control system.

[0014] Optionally, the first inlet of the nitrate tank is connected to the outlet of the mixed liquid tank via a first brine pipe. The first brine pipe is equipped with a salt discharge pump and a preheater in sequence along the material flow direction. The outlet of the nitrate tank is connected to the inlet of the MVR evaporation system via a sixth brine pipe.

[0015] Optionally, the MVR evaporation system includes an evaporation tank and a salt leg washing pipe connected in sequence, with the outlet of the nitrate tank connected to the inlet of the evaporation tank; the inlet of the primary salt washer is connected to the outlet of the salt leg washing pipe through a first salt slurry pipe.

[0016] The inlet of the flash evaporation tank is connected to the outlet of the evaporation tank via a second brine pipe, and the outlet of the flash evaporation tank is connected to the third inlet of the mixing tank via a third brine pipe.

[0017] Optionally, the salt washing system further includes a second washing tank and a third washing tank, wherein the second washing tank is located between the first-stage salt washing device and the second-stage salt washing device, and the third washing tank is located between the third-stage salt washing device and the second-stage salt washing device;

[0018] The first outlet of the three washing tank is connected to the first inlet of the secondary salt washing device via a fourth brine pipe, and the second outlet of the three washing tank is connected to the inlet of the salt leg washing pipe via a fifth brine pipe.

[0019] Optionally, the high-temperature steam in the evaporator is washed by a gas scrubbing tower, and the washed secondary steam is heated and pressurized by a steam compressor, and then returned to the evaporator through a heating chamber.

[0020] Optionally, the condensate generated by the heating chamber and the gas scrubbing tower enters a condensate tank and then flows into the injection well in the mining area through the condensate tank.

[0021] Optionally, a first hydrocyclone is provided at the first inlet of the primary salt washing device, and the outlet of the first hydrocyclone is connected to the fourth inlet of the mixing tank;

[0022] A second hydrocyclone is provided at the first inlet of the secondary salt washing device, and the outlet of the second hydrocyclone is connected to the second inlet of the primary salt washing device;

[0023] A third cyclone separator is installed at the inlet of the three-stage salt washing device, and the outlet of the third cyclone separator is connected to the second inlet of the two-stage salt washing device.

[0024] Secondly, a method for nitrate removal using MVR and salting-out precipitation, employing the aforementioned MVR and salting-out precipitation system, includes the following steps:

[0025] The refined brine and salt slurry undergo three-stage countercurrent emulsification and flotation washing in the salt washing system. The washed salt slurry is dehydrated and dried by a centrifuge to become finished salt. The overflow liquid discharged from the three-stage salt washing device enters the mixing tank through the two-stage salt washing device and the first-stage salt washing device. The mother liquor from the evaporator is flash-cooled in the flash evaporation tank. The cooled mother liquor and the overflow liquid from the first-stage salt washing device enter the mixing tank together. They are then heated to a certain temperature by the salt discharge pump and the preheater and enter the nitrate tank. At the same time, salt is added to the mixing tank through the salt addition pipe at the bottom third outlet of the first-stage salt washing device to saturate sodium chloride and crystallize sodium sulfate.

[0026] Compared with the prior art, this application has at least the following beneficial effects:

[0027] 1. Based on further analysis and research of existing technical problems, this application provides an MVR and salt precipitation nitrate system. By eliminating the existing salt addition pipeline from the evaporator's salt discharge pump to the nitrate tank, a new, independent, precision salt addition subsystem originating from the salt washer is added. This subsystem includes a first brine pipeline from the mixed liquor tank to the nitrate tank, and the newly added salt addition pipeline from the first-stage salt washer to the mixed liquor tank. A flow meter and an electric regulating valve are sequentially installed on this salt addition pipeline, and the flow meter and electric regulating valve are electrically connected to a central control system. The flow meter monitors and reports the flow rate of the brine entering the nitrate tank in real time, sending the data to the control system. This, in turn, controls the electric regulating valve to automatically adjust and open / close the flow rate of the salt addition pipeline, thereby achieving directional and quantitative salt addition. Precise automatic salt addition: This application optimizes the existing design with fewer modifications and lower costs, enabling the stable and quantitative addition of fine-particle salt slurry into the nitrate tank. This optimizes the salting-out reaction conditions within the tank, resulting in the continuous production of high-purity sodium sulfate. The salt addition process is stable and controllable, significantly improving the quality of the nitrate product. Simultaneously, the salt source is changed to the outlet pipe of the salt washer, where the liquid has good flowability and stable pressure, avoiding the backpressure problem caused by high pressure differential in the nitrate tank and completely solving the pipe blockage issue. This ensures the continuity and stability of production. Furthermore, the salt slurry exiting the salt washer is washed fine salt with smaller particle size and a larger specific surface area, resulting in faster dissolution in the nitrate tank and higher efficiency in re-dissolving sodium sulfate, further promoting the improvement of nitrate quality.

[0028] 2. This application also draws out a stream of brine with a lower temperature (approximately 36°C) from the second outlet of the third washing tank, and transports it to the inlet of the salt leg washing pipe through the fifth brine pipeline. This effectively cools the high-temperature salt slurry in the salt leg washing pipe. This design not only stabilizes the operating temperature of the salt leg washing pipe, but also creates suitable conditions for subsequent processes. At the same time, it avoids putting all the cooling load on the flash evaporation tank, thereby solving the problem of the salt discharge pump tripping due to the overload of the flash evaporation tank and ensuring the continuous and stable operation of the system. Attached Figure Description

[0029] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).

[0030] Figure 1 A schematic diagram of the structure of the MVR and salting-out nitrate precipitation system provided in the prior art of this application;

[0031] Figure 2A schematic diagram of the structure of an MVR and salting-out nitrate precipitation system provided in one embodiment of this application. Figure 1 (Without pipeline labels);

[0032] Figure 3 A schematic diagram of the structure of an MVR and salting-out nitrate precipitation system provided in one embodiment of this application. Figure 2 (with pipeline numbers);

[0033] Figure 4 for Figure 1 A partial schematic diagram of the area from the primary salt washing unit to the nitrate tank.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1. Nitrogen tank; 2. MVR evaporation system; 201. Evaporator; 202. Salt leg washing pipe; 203. Heating chamber; 3. Flash evaporation tank; 4. Salt washing system; 401. Primary salt washer; 402. Secondary salt washer; 403. Tertiary salt washer; 404. Secondary washing tank; 405. Tertiary washing tank; 5. Mixing tank; 6. Gas scrubbing tower; 7. Steam compressor; 8. Centrifuge; 9. First hydrocyclone; 10. Second hydrocyclone; 11. Third hydrocyclone; 12. Condensate tank; 13. Mine injection well;

[0036] 14. Salt addition pipe; 15. First brine pipe; 16. Second brine pipe; 17. Third brine pipe; 18. Fourth brine pipe; 19. Fifth brine pipe; 20. Sixth brine pipe; 21. First brine pipe; 22. Second brine pipe; 23. Third brine pipe; 24. Fourth brine pipe; 25. Fifth brine pipe; 26. Sixth brine pipe; 27. Seventh brine pipe; 28. Eighth brine pipe; 29. ​​First steam pipe; 30. Second steam pipe; 31. Third steam pipe; 32. First condensate pipe; 33. Second condensate pipe;

[0037] 34. Salt discharge pump; 35. Preheater; 36. Flow meter; 37. Electric regulating valve. Detailed Implementation

[0038] The present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0039] In the description of this application: unless otherwise stated, "a plurality of" means two or more. The terms "first," "second," "third," etc., in this application are intended to distinguish the objects referred to and do not have any special meaning in terms of technical connotation (e.g., they should not be construed as an emphasis on importance or order). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0040] The terms used in this application, such as "upper," "lower," "left," "right," and "middle," are generally used to indicate the general relative positional relationship for the purpose of intuitive understanding by referring to the accompanying drawings, and are not absolute limitations on the positional relationship in the actual product.

[0041] One embodiment of this application is shown below. Figures 2-4 An MVR and salting-out nitrate precipitation system includes: an MVR evaporation system 2, a flash evaporation tank 3, a nitrate tank 1, a salt washing system 4, a mixing tank 5, a salt adding pipe 14, and several connecting pipes for connecting the various devices.

[0042] The salt washing system 4 includes a primary salt washer 401, a secondary salt washer 402, and a tertiary salt washer 403 connected in sequence. The first and second inlets of the tertiary salt washer 403 are connected to refined brine and salt slurry, respectively, and the outlet of the tertiary salt washer 403 is connected to a centrifuge 8. The first and second outlets of the primary salt washer 401 are connected to the first inlet of the secondary salt washer 402 and the first inlet of the mixing tank 5, respectively. The third outlet of the primary salt washer 401 is connected to the second inlet of the mixing tank 5 through a salt addition pipe 14. The third inlet of the mixing tank 5 is connected to the outlet of the flash evaporation tank 3. The first inlet of the primary salt washer 401 is connected to the first outlet of the MVR evaporation system 2, and the second outlet of the MVR evaporation system 2 is connected to the inlet of the flash evaporation tank 3. The inlet of the nitrate tank 1 is connected to the outlet of the mixing tank 5, and the outlet of the nitrate tank 1 is connected to the inlet of the MVR evaporation system 2.

[0043] A flow meter 36 and an electric regulating valve 37 are sequentially installed along the material flow direction on the salt addition pipeline 14. Both the flow meter 36 and the electric regulating valve 37 are electrically connected to the control system.

[0044] Preferably, the first inlet of the nitrate tank 1 is connected to the outlet of the mixing tank 5 via a first brine pipe 21. The first brine pipe 21 is equipped with a salt discharge pump 34 and a preheater 35 in sequence along the material flow direction. The preheater 35 preheats the brine to about 102°C through three stages of preheating. The outlet of the nitrate tank 1 is connected to the inlet of the MVR evaporation system 2 via a sixth brine pipe 26.

[0045] This application eliminates the existing salt addition pipeline from the evaporator's salt discharge pump to the nitrate tank in the design and adds a new independent precision salt addition subsystem originating from the salt washer. This subsystem includes: a salt addition pipeline 14 between the primary salt washer 401 and the mixing tank 5, a first brine pipeline 21 between the mixing tank 5 and the nitrate tank 1, and an electric regulating valve 37 and a flow meter 36 installed on the salt addition pipeline 14. Both the flow meter 36 and the electric regulating valve 37 are electrically connected to the existing central control system (DCS). The flow meter 36 is located at the front or rear end of the electric regulating valve 37 and is used to monitor and provide feedback on the flow rate of the salt slurry entering the nitrate tank 1 in real time. The electric regulating valve 37 is used to receive control signals and automatically adjust and open / close the flow rate of the salt addition pipeline 14.

[0046] The operator can set a desired salt addition flow rate in the control system. When the system is running, the flow meter 36 detects the actual flow rate in real time and transmits the signal to the control system. The control system compares the actual value with the preset salt addition flow rate and controls the opening of the electric regulating valve 37 so that the actual salt addition flow rate is stably maintained near the set value, thereby realizing closed-loop automatic control and thus directional, quantitative and precise automatic salt addition.

[0047] Through the above modifications, fine-particle salt slurry is stably and quantitatively added to nitrate tank 1, achieving optimal salting-out reaction conditions within tank 1, thereby continuously producing high-purity sodium sulfate. Compared with existing technologies, it has at least the following advantages:

[0048] (1) Significantly improved product quality: By controlling the amount of salt added stably and precisely, the optimal conditions for salt precipitation were provided for the nitrate tank, which improved the resolution and washing effect of sodium sulfate. The final product main content (Na2SO4) can be stably increased to more than 92%, meeting the national qualified product standard, which greatly improved the product value and economic benefits.

[0049] (2) Completely solve the problem of pipeline blockage: Since the salt source is changed to the outlet pipeline of the salt washing machine, the liquid has good fluidity and stable pressure, avoiding the problem of back pressure of the high pressure difference of the nitrate tank, fundamentally eliminating the hidden danger of pipeline blockage, and ensuring the continuity and stability of production.

[0050] (3) Stable and controllable salt addition: The independent salt addition pipeline is dedicated to its own use, avoiding mutual interference with the raw salt production system; through the combination of "flow meter + electric regulating valve", real-time monitoring and precise adjustment of the salt addition process are realized, greatly enhancing the process controllability.

[0051] (4) Improve salt dissolution efficiency: The salt slurry from the first-stage salt washing machine is fine salt that has been washed, with smaller particle size and larger specific surface area. It dissolves faster in the nitrate tank and has a higher efficiency in re-dissolving Glauber's salt, which further promotes the improvement of nitrate quality.

[0052] (5) Simple transformation and low cost: No need to modify the core equipment, easy to implement, low investment cost, very suitable for the technical transformation of existing production lines, and extremely cost-effective.

[0053] Preferably, the MVR evaporation system 2 includes an evaporation tank 201 and a salt leg washing pipe 202 connected in sequence, with the outlet of the nitrate tank 1 connected to the inlet of the evaporation tank 201; the inlet of the primary salt washer 401 is connected to the outlet of the salt leg washing pipe 202 through the first salt slurry pipe 15.

[0054] The inlet of the flash evaporation tank 3 is connected to the outlet of the evaporation tank 201 via the second brine pipe 22, and the outlet of the flash evaporation tank 3 is connected to the third inlet of the mixing tank 5 via the third brine pipe 23.

[0055] Preferably, the salt washing system 4 further includes a second washing tank 404 and a third washing tank 405. The second washing tank 404 is located between the first-stage salt washing unit 401 and the second-stage salt washing unit 402, and is connected in sequence through corresponding brine pipes. The third washing tank 405 is located between the third-stage salt washing unit 403 and the second-stage salt washing unit 402, and is connected in sequence through corresponding brine pipes.

[0056] The first outlet of the third washing tank 405 is connected to the first inlet of the secondary salt washer 402 via the fourth brine pipe 24, and the second outlet of the third washing tank 405 is connected to the inlet of the salt leg washing pipe 202 via the fifth brine pipe 25. A stream of lower-temperature brine (approximately 36°C) is drawn from the second outlet of the third washing tank 405 and transported to the inlet of the salt leg washing pipe 202 via the fifth brine pipe 25. The core function of this low-temperature brine is to effectively cool the high-temperature salt slurry inside the salt leg washing pipe 202. This design not only stabilizes the operating temperature of the salt leg washing pipe 202 but also creates suitable conditions for subsequent processes. It also avoids placing all the cooling load on the flash evaporation tank 3, thus solving the problem of the salt discharge pump 34 tripping due to overload of the flash evaporation tank 3, and ensuring the continuous and stable operation of the system.

[0057] Preferably, a first hydrocyclone 9 is provided at the first inlet of the primary salt washing unit 401. The outlet of the first hydrocyclone 9 is connected to the fourth inlet of the mixing tank 5 through an eighth brine pipe 28. The first hydrocyclone 9 performs solid-liquid separation on the salt slurry before it enters the primary salt washing unit 401. After separation, the liquid flows out, which is actually high in sodium sulfate and enters the mixing tank 5 through the eighth brine pipe 28. The second outlet of the primary salt washing unit 401 is connected to the first inlet of the mixing tank 5 through a seventh brine pipe 27. A second hydrocyclone 10 is provided at the first inlet of the secondary salt washing unit 402. The outlet of the second hydrocyclone 10 is connected to the second inlet of the primary salt washing unit 401 through a fifth salt slurry pipe 19.

[0058] A third hydrocyclone 11 is installed at the inlet of the third-stage salt washer 403, and the outlet of the third hydrocyclone 11 is connected to the second inlet of the second-stage salt washer 402 through a sixth salt slurry pipe 20.

[0059] The first inlet of the aforementioned three-stage salt washing device 403 is located at the bottom of its main body, the second inlet of the three-stage salt washing device 403 is located at the top of its main body, and the outlet of the three-stage salt washing device 403 is located at the bottom of its main body. The first hydrocyclone 9, the second hydrocyclone 10, and the third hydrocyclone 11 are respectively located at the upper inlet ends of the first-stage salt washing device 401, the second-stage salt washing device 402, and the third-stage salt washing device 403. The first outlet at the bottom of the first-stage salt washing device 401 is connected to the inlet of the second hydrocyclone 10 at the top of the second-stage salt washing device 402 through the second salt slurry pipe 16. The first outlet at the bottom of the second-stage salt washing device 402 is connected to the inlet of the third hydrocyclone 11 at the top of the third-stage salt washing device 403 through the third salt slurry pipe 17. The bottom outlet of the third-stage salt washing device 403 is connected to the centrifuge 8 through the fourth salt slurry pipe 18. The washed salt slurry is dehydrated and dried by the centrifuge 8 to become finished salt.

[0060] Preferably, the high-temperature steam from the evaporator 201 is washed by the gas scrubbing tower 6, and the washed secondary steam is heated and pressurized by the steam compressor 7, and then returned to the evaporator 201 through the heating chamber 203.

[0061] The high-temperature steam from the evaporator 201 is connected to the inlet of the gas scrubbing tower 6 via the first steam pipe 29. The outlet of the gas scrubbing tower 6 is connected to the inlet of the steam compressor 7 via the second steam pipe 30. The outlet of the steam compressor 7 is connected to the heating chamber 203 via the third steam pipe 31. The heating chamber 203 is used to heat the evaporator 201.

[0062] More preferably, the condensate generated by the heating chamber 203 and the gas scrubbing tower 6 enters the condensate tank 12 through the first condensate pipe 32 and the second condensate pipe 33, respectively, and then enters the mine injection well 13 through the condensate tank 12.

[0063] This application achieves effective cooling of the salt slurry in the salt washing pipe 202, after which the salt slurry directly enters the salt washing system 4 through the first salt slurry pipe 15. The raw brine and salt slurry undergo three-stage countercurrent emulsification and flotation washing in the salt washing device. The washed salt slurry is directly centrifuged, dehydrated, dried, and packaged as finished salt. The salt slurry concentration at the bottom of the first-stage salt washing device 401 (always around 50%) is very stable. At this stable concentration (around 50%) and stable flow rate (6-13 m³ / h), it enters the mixing tank 5 through the salt addition pipe 14. The mixing tank 5 is full of saturated sodium sulfate, forming a common ion effect. During this process, the temperature is raised to the nitrate tank 1 (102-105℃) through the preheater 35, and then the reaction takes place in the nitrate tank 1, causing the nitrate product to precipitate. The overflowing clear sodium chloride re-enters the MVR evaporation system 2 through the sixth brine pipe 26 as the feed liquid for the MVR evaporation system 2.

[0064] Furthermore, through the reverse washing action of the raw brine, some solid impurities dissolve in the brine. Due to the different particle sizes in the solid phase, sodium chloride particles are much larger than the impurities, causing sodium chloride crystals to settle. Most of the solid impurities are separated with the overflow of the mother liquor. By designing a reasonable salt washing device, a salt slurry that meets the quality requirements can be obtained after washing. To obtain stable product quality, a small amount of mother liquor needs to be discharged from the MVR evaporation system 2. The mother liquor discharged from the flash tank 3 and the overflow liquid from the first-stage salt washing device 401 discharged through the seventh brine pipe 27 enter the mixing tank 5 together. After three-stage preheating, the mother liquor is heated to a suitable temperature and enters the nitrate tank 1. Salt is added simultaneously to the mixing tank 5 through the salt addition pipe 14. When sodium chloride reaches saturation, according to the principle of the common ion effect, sodium sulfate will be affected by the common ion Na+. + Supersaturation causes a common ion effect, resulting in the crystallization of sodium sulfate and the precipitation of sodium chloride, which is far from the saturation point and does not precipitate. During this process, a small amount of magnesium sulfate and calcium sulfate contained in the brine also crystallize out. The crystallized sodium sulfate is then removed, centrifuged, dehydrated, dried, and packaged as the finished product, nitrate.

[0065] This application also provides an MVR and salting-out method for nitrate precipitation, employing the above-mentioned MVR and salting-out system, comprising the following steps:

[0066] The refined brine and salt slurry undergo a three-stage countercurrent emulsification and flotation washing process within the salt washing system 4. Taking the three-stage salt washer 403 as an example, the refined brine enters from the bottom of the three-stage salt washer 403, and the salt slurry enters from the top of the three-stage salt washer 403, forming a countercurrent washing process. The washed salt slurry is dehydrated and dried by the centrifuge 8 to become finished salt. The overflow liquid discharged from the three-stage salt washer 403 flows sequentially through the three washing tanks 405, the two-stage salt washer 402, the two-stage washing tank 404, the one-stage salt washer 401, and the seventh brine pipe 27 into the mixed liquid tank 5. The second outlet of the three washing tanks 405 also transports brine at approximately 36°C to the inlet of the salt leg washing pipe 202 through the fifth brine pipe 25 to cool down the high-temperature salt slurry in the salt leg washing pipe 202. After cooling, the salt slurry flows sequentially through the first salt slurry pipe 15 into the one-stage salt washer 401, the two-stage salt washer 402, and the three-stage salt washer 403 of the salt washing system 4.

[0067] The mother liquor from evaporator 201 enters flash evaporation tank 3 through second brine pipe 22 for flash evaporation and cooling. The cooled mother liquor, along with the overflow liquid from primary brine washer 401 (which is the clear liquid after salt washing and has a relatively high sodium sulfate content) entering through seventh brine pipe 27, enters mixing tank 5. It is then heated to approximately 102°C by salt discharge pump 34 and preheater 35 (three-stage preheating) before entering nitrate tank 1. Simultaneously, salt is added to mixing tank 5 through salt addition pipe 14 from the third outlet at the bottom of primary brine washer 401 to saturate sodium chloride, while sodium sulfate is added due to the presence of common ions Na+. +Supersaturation causes the common ion effect, resulting in the precipitation of sodium sulfate crystals. The salt slurry added to the mixed liquid tank 5 by the primary salt washing device 401 through the salt addition pipe 14 is washed, resulting in finer salt particles with smaller particle size and larger specific surface area, which makes the dissolution rate in the nitrate tank 1 faster and the redissolution efficiency of sodium sulfate higher.

[0068] The technical features of the above embodiments can be combined in any way (as long as there is no contradiction in the combination of these technical features). For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written should also be considered to be within the scope of this specification.

Claims

1. A system for MVR and salting-out nitrate, characterized in that, It comprises: The MVR evaporation system, flash tank, nitrate tank, salt washing system, mixed liquid barrel, salt adding pipeline and several connecting pipelines; The salt washing system comprises a first-stage salt washing device, a second-stage salt washing device and a third-stage salt washing device connected in sequence, the first inlet and the second inlet of the third-stage salt washing device are connected with refined brine and salt slurry respectively, and the outlet of the third-stage salt washing device is connected with a centrifuge; the first outlet and the second outlet of the first-stage salt washing device are connected with the first inlet of the second-stage salt washing device and the first inlet of the mixed liquid barrel respectively, the third outlet of the first-stage salt washing device is connected with the second inlet of the mixed liquid barrel through the salt adding pipeline, and the third inlet of the mixed liquid barrel is connected with the outlet of the flash tank; the first inlet of the first-stage salt washing device is connected with the first outlet of the MVR evaporation system, and the second outlet of the MVR evaporation system is connected with the inlet of the flash tank; the inlet of the nitrate tank is connected with the outlet of the mixed liquid barrel, and the outlet of the nitrate tank is connected with the inlet of the MVR evaporation system; A flow meter and an electric regulating valve are arranged on the salt adding pipeline in sequence, and the flow meter and the electric regulating valve are electrically connected with a control system.

2. The MVR and salting-out system for nitrate analysis according to claim 1, wherein, The first inlet of the nitrate tank is connected with the outlet of the mixed liquid barrel through a first brine pipeline, the first brine pipeline is sequentially provided with a salt discharging pump and a preheater along the material flow direction, and the outlet of the nitrate tank is connected with the inlet of the MVR evaporation system through a sixth brine pipeline.

3. The MVR and salting-out system for nitrate separation according to claim 1, wherein, The MVR evaporation system comprises an evaporation tank and a salt leg washing pipe connected in sequence, the outlet of the nitrate tank is connected with the inlet of the evaporation tank, and the inlet of the first-stage salt washing device is connected with the outlet of the salt leg washing pipe through a first salt slurry pipeline. The inlet of the flash tank is connected with the outlet of the evaporation tank through a second brine pipeline, and the outlet of the flash tank is connected with the third inlet of the mixed liquid barrel through a third brine pipeline.

4. The MVR and salting-out system for nitrate analysis according to claim 3, wherein, The salt washing system further comprises a second-stage washing barrel and a third-stage washing barrel, the second-stage washing barrel is located between the first-stage salt washing device and the second-stage salt washing device, and the third-stage washing barrel is located between the third-stage salt washing device and the second-stage salt washing device; The first outlet of the third-stage washing barrel is connected with the first inlet of the second-stage salt washing device through a fourth brine pipeline, and the second outlet of the third-stage washing barrel is connected with the inlet of the salt leg washing pipe through a fifth brine pipeline.

5. The MVR and salting-out system for nitrate separation according to claim 3, wherein, High-temperature steam of the evaporation tank is washed through a gas washing tower, secondary steam after washing is heated and pressurized through a steam compressor, and then flows back to the evaporation tank through a heating chamber.

6. The MVR and salting-out system for nitrate analysis according to claim 5, wherein, Condensed water generated by the heating chamber and the gas washing tower flows into a condensed water barrel and then flows into a mine area injection well through the condensed water barrel.

7. The MVR and salting-out system of claim 1, wherein, A first cyclone is arranged at the first inlet of the first-stage salt washing device, and the outlet of the first cyclone is connected with the fourth inlet of the mixed liquid barrel; A second cyclone is arranged at the first inlet of the second-stage salt washing device, and the outlet of the second cyclone is connected with the second inlet of the first-stage salt washing device; A third cyclone is arranged at the inlet of the third-stage salt washing device, and the outlet of the third cyclone is connected with the second inlet of the second-stage salt washing device.

8. A method of MVR and salting-out nitrate separation, characterized in that, The MVR and salt analysis nitrate system of claim 1 comprises the following steps: The refined brine and salt slurry are subjected to three-stage countercurrent emulsification and floating washing in a salt washing system, the washed salt slurry is dewatered by a centrifuge and dried to become finished product salt, overflow liquid discharged from the three-stage salt washing device enters a mixed liquid barrel through the secondary salt washing device and the primary salt washing device in sequence, mother liquor of the evaporation tank is subjected to flash evaporation and cooling in a flash tank, the cooled mother liquor and overflow liquid of the primary salt washing device enter the mixed liquid barrel together, and are heated and warmed to a certain temperature by a salt discharge pump and a preheater to enter a nitration tank, at the same time, the bottom third outlet of the primary salt washing device synchronously adds salt in the mixed liquid barrel through a salt adding pipeline to make sodium chloride saturated, and sodium sulfate is crystallized and separated out.

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