Preparation method of continuous co-crystallized low-sodium salt

Abstract

The invention belongs to the technical field of inorganic salt industry, and particularly relates to a preparation method of continuous co-crystallized low-sodium salt, which comprises the following steps: solution preparation, evaporative crystallization, solid-liquid separation, drying and the like. According to the preparation method, co-crystallization and continuous production processes of sodium chloride and potassium chloride are realized by optimizing a production process, the obtained low-sodium salt is uniform in particle size distribution, the mixing uniformity, the content range and the product stability of the sodium chloride and the potassium chloride in the product are greatly improved, the process is simple, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic salt industry, and particularly relates to a method for preparing a continuous co-crystallized low-sodium salt. Background Art

[0002] With the improvement of people's living conditions and the emphasis on health concepts, low-sodium salt has gradually become popular. As the future development direction of condiments, it has broad development prospects and market development.

[0003] At present, the preparation methods of low sodium salt mainly include direct mixing method, seawater or brine evaporation method and salt soil plant leaching method. Among them, the direct mixing method is to mix the raw materials according to the formula ratio by mechanical mixing process, but this method has the problem that sodium chloride and potassium chloride cannot be mixed evenly, especially potassium chloride is unevenly distributed, and the content range is difficult to control, which reduces the taste of low sodium salt products; at the same time, food additives are added to low sodium salt products to mask bitterness or prevent caking, which does not meet the requirements of natural green products, and food additives are expensive, which will increase the manufacturing cost of low sodium salt.

[0004] Therefore, it is urgent to provide a preparation method that can make potassium chloride and sodium chloride evenly distributed and controllable in content. Summary of the invention

[0005] In view of the deficiencies in the prior art, the object of the present invention is to provide a method for preparing a continuously co-crystallized low-sodium salt. The preparation method realizes the co-crystallization of sodium chloride and potassium chloride by optimizing the production process and equipment. The obtained low-sodium salt not only has a uniform particle size distribution, but also greatly improves the mixing uniformity, content range and product stability of sodium chloride and potassium chloride in the product.

[0006] The object of the present invention is to provide a method for preparing a continuous co-crystallized low sodium salt, comprising the following steps: S1. The solid raw materials of sodium chloride and potassium chloride are transported to the salt distribution tank through a spiral feeding device, and the reverse osmosis water is pumped to the salt distribution tank, and the salt is fully dissolved and salted by mechanical stirring to obtain a saturated raw material liquid; S2. The saturated raw material liquid obtained in S1 is transported to a tubular heat exchanger, and after two stages of heat exchange, is transported to a tubular evaporator, and an MVR evaporation crystallization method is adopted. After evaporation and concentration under the joint promotion of a heat source and a negative pressure environment, the liquid is sent to a forced circulation crystallizer for crystallization, wherein the low-solid content material at the top of the crystallizer is withdrawn to the evaporator for circulation and concentration, and then returned to the crystallizer, and the material is discharged from the bottom to obtain a crystal slurry; S3. The slurry obtained in S2 is separated by a centrifuge to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are transported to a ZLG vibrating fluidized bed dryer for drying and screening to obtain low sodium salt.

[0007] After preliminary work, the inventor used the Oslo crystallizer as a crystallizer, which is characterized in that the upper clear liquid is circulated, and the bottom of the crystallizer is a sedimentation zone, and large particles slowly settle down. Although a certain co-crystallization effect of potassium chloride and sodium chloride can be achieved through condition control, due to the limitation of the solid content of the crystallizer, after sampling and analysis at different positions, it was found that there was a more significant particle size and content stratification phenomenon in the crystallizer. The bottom discharge of the crystallizer is mainly large sodium chloride particles with less potassium chloride content; the middle discharge is particles of potassium chloride and sodium chloride grown together, with large particles and small particles, and a certain distribution of particle sizes; and the upper discharge is mainly small potassium chloride particles with less sodium chloride content. The product of each part of the discharge is unstable, and the discharge needs to be timely after evaporation for a period of time, and continuous production cannot be carried out.

[0008] Therefore, the inventor optimizes the specific processing technology and equipment, directly adds solid as raw material into the salt preparation tank in a quantitative manner, and the operation method uses water that has been subjected to reverse osmosis to dissolve the salt, and no additional impurities are introduced; the heat transfer and evaporation efficiency of the evaporator can be improved by two-stage preheating, thereby reducing costs; by controlling conditions such as evaporation temperature and pressure, concentration without crystallization is achieved, thereby improving the concentration efficiency; and then by using a forced circulation crystallizer and controlling its vacuum degree and circulation rate, the purpose of continuous production is achieved, wherein when entering the lower part of the crystallizer, due to the influence of temperature, gravity, etc., sodium chloride is used as a seed during crystallization, and then sodium chloride and potassium chloride are epitaxially grown on its surface at the same time, thereby achieving the purpose of co-crystallization, and by controlling the bottom discharge speed, not only can continuity be achieved, but the obtained low-sodium salt product has a uniform particle size distribution, which can meet the international requirements for low-sodium salt, and at the same time, due to the co-crystallization growth of sodium chloride and potassium chloride, potassium chloride is evenly distributed and has a stable content range. Specifically, the raw materials for preparing low-sodium salt are food grade, among which the main chemical composition of food-grade sodium chloride is 98-99.8% NaCl, 0.1-0.5% Na2SO4, and 0.1-1.5% other impurities; the main chemical composition of food-grade potassium chloride is 97-99% KCl, 0.5-1.0% NaCl, and 0.5-2.0% other impurities.

[0009] Preferably, in the above technical solution S1, the saturated raw material liquid comprises, by mass percentage, 15.58±0.5% sodium chloride, 8.14±0.2% potassium chloride, and 76.28±0.5% water.

[0010] Preferably, in the above technical solution S1, the reverse osmosis water is purified by using an RO membrane, the inlet pressure is 1.0 MPa, and the RO water production flow rate is 1-1.2 m 3 / h, concentrated water flow rate is 0.9-1.0m 3 / h. In this technical solution, RO membrane is used to purify water, which can effectively prevent the introduction of impurities. At the same time, by controlling the pressure and flow, the penetration effect is good.

[0011] Preferably, in the above technical solution S2, the two-stage heat exchange method is: the saturated raw material liquid is firstly heat exchanged with the system evaporation condensed water in the first stage, and then heat exchanged with the secondary non-condensable gas in the tube evaporator condensed water gas-liquid separation tank in the second stage; the MVR evaporation crystallization process conditions are: continuous feeding, the feeding rate is controlled to be 0.2-0.3m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 85-90%, the current at 55-60A, and the evaporation rate at 0.3-0.35m 3 / h, the evaporation temperature is controlled at 80-85℃.

[0012] Preferably, in the above technical solution S2, the forced circulation crystallizer is of FC type, the vacuum degree of the crystallizer is 0.07-0.08MPa, and the circulation volume of the crystal slurry corresponding to the circulation pump is 85-90m 3 / h.

[0013] In this technical solution, an FC type forced circulation crystallizer is adopted. The crystallization chamber has a conical bottom. After the slurry is discharged from the conical bottom, it is pumped through the heat exchanger by an axial flow circulation pump through the circulation pipe, and re-enters the crystallization chamber after being heated or cooled. By controlling the vacuum degree and circulation volume of the crystallizer, sodium chloride is first crystallized, and then sodium chloride and potassium chloride continue to grow epitaxially on the surface during the sinking process to form eutectic particles of sodium chloride and potassium chloride.

[0014] Preferably, in the above technical solution S2, the bottom continuous discharge rate is 0.1-0.2m 3 / h. In this technical solution, by controlling the discharge speed and the solid content in the crystallizer, the particle size and particle size distribution of the low sodium salt can be effectively controlled, and continuous production can be achieved.

[0015] Preferably, in the above technical solution S3, the centrifuge is a horizontal centrifuge, the centrifugation frequency is 30 Hz, and the centrifugation time is 3-4 min.

[0016] Preferably, in the above technical solution S4, the inlet air temperature of the fluidized bed dryer is controlled to be 120±2°C, the bed temperature is 100±2°C, the blower frequency is 50Hz, the induced draft fan frequency is 40Hz, the vibration motor frequency is 30Hz, and the conveyor frequency is 35Hz.

[0017] Preferably, in the above technical solution S4, the low sodium salt is cubic eutectic particles, sodium chloride is used as a seed crystal, and sodium chloride and potassium chloride are epitaxially eutectic grown.

[0018] Preferably, in the above technical solution S4, the KCl content in the low sodium salt is 25-35%; the particle size distribution range is: the proportion of solid particles larger than 0.9 mm is ≥47%, and the proportion of solid particles larger than 0.55 mm is ≥83%.

[0019] Advantages compared to the prior art: 1. The present invention uses solid as raw material and directly adds it to the salt preparation tank in a quantitative manner. The operation method uses water that has been subjected to reverse osmosis to dissolve the salt, and no additional impurities are introduced. The heat transfer and evaporation efficiency of the evaporator can be improved by two-stage preheating, thereby reducing costs. By controlling conditions such as evaporation temperature and pressure, concentration without crystallization is achieved, thereby improving the concentration efficiency. Then, a forced circulation crystallizer is used and its vacuum degree and circulation rate are controlled to achieve the purpose of continuous production. Since the lower part of the crystallizer is affected by temperature, gravity, etc., sodium chloride is used as a seed during crystallization, and then sodium chloride and potassium chloride are simultaneously epitaxially grown on its surface, thereby achieving the purpose of co-crystallization and improving the stability of the product.

[0020] 2. The present invention realizes the co-crystallization of sodium chloride and potassium chloride by optimizing the production process and the discharging method. The obtained low sodium salt not only has a uniform particle size distribution, but also greatly improves the mixing uniformity of sodium chloride and potassium chloride in the product. It can be seen from the surface morphology of the product and the corresponding energy spectrum analysis diagram that most of the sodium elements are relatively evenly distributed on the surface of large particles, and a small part of the potassium elements are scattered on the surface of large particles, indicating that the large particles are mainly composed of sodium chloride and potassium chloride is co-embedded in an epitaxial growth manner. Sodium chloride and potassium chloride grow on the same large particle in a eutectic manner to form a eutectic, rather than simple particle agglomeration of sodium chloride and potassium chloride, so that the product is more stable.

[0021] 3. The present invention controls the concentration of the stock solution and the processing technology, so that the potassium chloride content in the obtained low sodium salt is stabilized between 25-35%, and the particle size distribution is uniform, which can meet the international requirements for low sodium salt. At the same time, the processing technology is simplified, continuous production can be achieved, the cost is low, and the market prospect is considerable. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 200 μm SEM-EDS of the low sodium salt product of Example 1 of the present invention (wherein a is a SEM image of the low sodium salt, b is the Na element distribution, c is the K element distribution, d is the Cl element distribution, and e is the overall distribution of Na, K, and Cl); Figure 2 200 μm SEM-EDS of the low sodium salt product of Example 1 of the present invention (wherein a is a SEM image of the low sodium salt, b is the Na element distribution, c is the K element distribution, d is the Cl element distribution, and e is the overall distribution of Na, K, and Cl); Figure 3 This is a 200 μm scanning electron microscope-energy spectrum diagram of the low sodium salt product of Example 1 of the present invention (wherein, a is a scanning electron microscope diagram of the low sodium salt, b is the Na element distribution, c is the K element distribution, d is the Cl element distribution, and e is the overall distribution of Na, K, and Cl). DETAILED DESCRIPTION

[0022] The above-mentioned technical features of the present invention and the technical features specifically described below (such as implementation cases) can be combined with each other to form new or preferred technical solutions, but the present invention is not limited to these embodiments, and these embodiments do not limit the present invention in any way.

[0023] The experimental methods in the following examples are conventional methods unless otherwise specified. The preparations involved in the following examples are common commercial products unless otherwise specified and can be purchased from the market.

[0024] The present invention is described in further detail below in conjunction with embodiments: Example 1 A method for preparing a continuous co-crystallized low sodium salt comprises the following specific steps: S1. Sodium chloride and potassium chloride solid raw materials are transported to the salt distribution tank through the spiral feeding equipment, and the reverse osmosis water is pumped to the salt distribution tank. After mechanical stirring, they are fully dissolved and salted to obtain saturated raw material liquid. The reverse osmosis water is purified by RO membrane, the inlet pressure is 1.0MPa, and the RO water flow rate is 1.2m 3 / h, concentrated water flow rate is 1.0m 3 / h, the saturated raw liquid contains 15.58% sodium chloride, 8.14% potassium chloride and 76.28% water; S2. The saturated raw material liquid obtained in S1 is transported to the tubular heat exchanger. The saturated raw material liquid first exchanges heat with the system evaporation condensed water in the first stage, and then exchanges heat with the secondary non-condensable gas in the condensed water gas-liquid separation tank of the tubular evaporator in the second stage. After two stages of heat exchange, it is transported to the tubular evaporator. The MVR evaporation crystallization process is adopted, and the continuous feeding and feeding rate are controlled to 0.2m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 90%, the current at 55A, and the evaporation rate at 0.3m 3 / h, the evaporation temperature is 80℃, after evaporation and concentration, it is sent to the forced circulation crystallizer for crystallization, the vacuum degree is 0.07MPa, and the circulation volume of the circulation pump is 85m 3 / h, the bottom continuous discharge rate is 0.1m 3 / h, to obtain slurry; S3. The slurry obtained in S2 is separated by a centrifuge at a centrifugal frequency of 30 Hz for 4 min to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are conveyed to a ZLG vibrating fluidized bed dryer. The air inlet temperature of the fluidized bed dryer is 120°C, the bed temperature is 100°C, the blower frequency is 50Hz, the induced draft fan frequency is 40Hz, the vibration motor frequency is 30Hz, and the conveyor frequency is 35Hz. After drying, the particles are sieved to obtain low sodium salt.

[0025] Example 2 A method for preparing a continuous co-crystallized low sodium salt comprises the following specific steps: S1. Sodium chloride and potassium chloride solid raw materials are transported to the salt distribution tank through the spiral feeding equipment, and the reverse osmosis water is pumped to the salt distribution tank. After mechanical stirring, they are fully dissolved and salted to obtain saturated raw material liquid. The reverse osmosis water is purified by RO membrane, the inlet pressure is 1.0MPa, and the RO water flow rate is 1m 3 / h, concentrated water flow rate is 0.9m 3 / h, the saturated raw liquid contains 15.08% sodium chloride, 8.34% potassium chloride and 76.58% water; S2. The saturated raw material liquid obtained in S1 is transported to the tubular heat exchanger. The saturated raw material liquid first exchanges heat with the system evaporation condensed water in the first stage, and then exchanges heat with the secondary non-condensable gas in the condensed water gas-liquid separation tank of the tubular evaporator in the second stage. After two stages of heat exchange, it is transported to the tubular evaporator. The MVR evaporation crystallization process is adopted, and the continuous feeding and feeding rate are controlled at 0.3m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 85%, current at 55A, evaporation rate at 0.35m 3 / h, the evaporation temperature is 85℃, after evaporation and concentration, it is sent to the forced circulation crystallizer for crystallization, the vacuum degree is 0.08MPa, and the circulation volume of the circulation pump is 90m 3 / h, the bottom continuous discharge rate is 0.2m 3 / h, to obtain slurry; S3. The slurry obtained in S2 is separated by a centrifuge at a centrifugal frequency of 30 Hz for 3 min to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are conveyed to a ZLG vibrating fluidized bed dryer. The air inlet temperature of the fluidized bed dryer is 120°C, the bed temperature is 100°C, the blower frequency is 50Hz, the induced draft fan frequency is 40Hz, the vibration motor frequency is 30Hz, and the conveyor frequency is 35Hz. After drying, the particles are sieved to obtain low sodium salt.

[0026] Example 3 A method for preparing a continuous co-crystallized low sodium salt comprises the following specific steps: S1. Sodium chloride and potassium chloride solid raw materials are transported to the salt distribution tank through the spiral feeding equipment, and the reverse osmosis water is pumped to the salt distribution tank. After mechanical stirring, they are fully dissolved and salted to obtain saturated raw material liquid. The reverse osmosis water is purified by RO membrane, the inlet pressure is 1.0MPa, and the RO water flow rate is 1.1m 3 / h, concentrated water flow rate is 0.9m 3 / h, the saturated raw liquid contains 15.38% sodium chloride, 8.24% potassium chloride and 76.38% water; S2. The saturated raw material liquid obtained in S1 is transported to the tubular heat exchanger. The saturated raw material liquid first exchanges heat with the system evaporation condensed water in the first stage, and then exchanges heat with the secondary non-condensable gas in the condensed water gas-liquid separation tank of the tubular evaporator in the second stage. After two stages of heat exchange, it is transported to the tubular evaporator. The MVR evaporation crystallization process is adopted, and the continuous feeding and feeding rate are controlled to 0.25m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 88%, current at 58A, evaporation rate at 0.3m 3 / h, the evaporation temperature is 85℃, after evaporation and concentration, it is sent to the forced circulation crystallizer for crystallization, the vacuum degree is 0.07MPa, and the circulation volume of the circulation pump is 88m 3 / h, the bottom continuous discharge rate is 0.15m 3 / h, to obtain slurry; S3. The slurry obtained in S2 is separated by a centrifuge at a centrifugal frequency of 30 Hz for 4 min to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are conveyed to a ZLG vibrating fluidized bed dryer. The air inlet temperature of the fluidized bed dryer is 120°C, the bed temperature is 100°C, the blower frequency is 50Hz, the induced draft fan frequency is 40Hz, the vibration motor frequency is 30Hz, and the conveyor frequency is 35Hz. After drying, the particles are sieved to obtain low sodium salt.

[0027] Comparative Example 1 A method for producing low-sodium salt comprises the following steps: S1. Sodium chloride and potassium chloride solid raw materials are transported to the salt distribution tank through the spiral feeding equipment, and the reverse osmosis water is pumped to the salt distribution tank. After mechanical stirring, they are fully dissolved and salted to obtain saturated raw material liquid. The reverse osmosis water is purified by RO membrane, the inlet pressure is 1.0MPa, and the RO water flow rate is 1.2m 3 / h, concentrated water flow rate is 1.0m 3 / h, the saturated raw liquid contains 15.58% sodium chloride, 8.14% potassium chloride and 76.28% water; S2. The saturated raw material liquid obtained in S1 is transported to the tubular heat exchanger. The saturated raw material liquid first exchanges heat with the system evaporation condensed water in the first stage, and then exchanges heat with the secondary non-condensable gas in the condensed water gas-liquid separation tank of the tubular evaporator in the second stage. After two stages of heat exchange, it is transported to the tubular evaporator. The MVR evaporation crystallization process is adopted, and the continuous feeding and feeding rate are controlled to 0.2m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 90%, the current at 55A, and the evaporation rate at 0.3m 3 / h, the evaporation temperature is 80℃, after evaporation and concentration, it is sent to the Oslo crystallizer for crystallization, the vacuum degree is 0.07MPa, and the circulation volume of the circulation pump is 85m 3 / h, with materials discharged from the top, middle and bottom respectively, and the discharge rate is 0.1m 3 / h, to obtain slurry; S3. The slurry obtained in S2 is separated by a centrifuge at a centrifugal frequency of 30 Hz for 4 min to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are conveyed to a ZLG vibrating fluidized bed dryer. The air inlet temperature of the fluidized bed dryer is 120°C, the bed temperature is 100°C, the blower frequency is 50Hz, the induced draft fan frequency is 40Hz, the vibration motor frequency is 30Hz, and the conveyor frequency is 35Hz. After drying, the particles are sieved to obtain low sodium salt.

[0028] According to the detection method of QB / T 2019-2020 low sodium salt standard, the component content of the low sodium salt obtained in Examples 1-3 and Comparative Example 1 was detected by a multi-point sampling method, and the results are shown in Table 1; the morphology and corresponding energy spectrum of the low sodium salt obtained in Examples 1-3 of the present invention were analyzed by scanning electron microscopy and energy dispersive spectrometer, and the results are shown in Table 1. Figure 1-3 shown.

[0029] Table 1 Ingredients and contents of low sodium salt

[0030] From the results in Table 1, it can be seen that the potassium chloride content of the low sodium salt prepared by the method of the present invention is between 25% and 35%, and the particle size distribution is uniform, which can meet the standard of QB / T 2019-2020 low sodium salt. In Comparative Example 1, due to the crystallizer, the upper, middle and bottom discharge products are not the same, wherein the upper part is mainly potassium chloride, and is mainly small particles, and although the middle part is relatively close to low sodium salt, the particle size is relatively uneven, and the bottom is mainly sodium chloride, and is mainly large particles, indicating that the product prepared by the preparation method of Comparative Example 1 is not stable, and it is difficult to meet the low sodium salt standard.

[0031] from Figure 1-3 It can be seen that the low sodium salt product prepared by the present invention has no agglomeration phenomenon, the product is smooth cubic particles, the surface is dense, potassium and sodium elements are evenly distributed, potassium is mainly distributed on the surface of the mother crystal, and at the same time is mutually interlocked with sodium, indicating that the low sodium salt prepared by the present invention uses the sodium chloride crystals formed at the beginning as seeds, then enters the sodium chloride and potassium chloride eutectic region, and mutually epitaxially grows to form eutectic particles.

[0032] In summary, the present invention optimizes the preparation process equipment and conditions to obtain low sodium salt sodium chloride and potassium chloride that are uniformly and stably mixed, wherein the potassium chloride content is stable between 25-35%, and the particle size distribution is uniform, which can meet the international requirements for low sodium salt.

[0033] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a continuous co-crystallized low sodium salt, characterized in that: The following steps are involved: S1. The solid raw materials of sodium chloride and potassium chloride are transported to the salt distribution tank through a spiral feeding device, and the reverse osmosis water is pumped to the salt distribution tank, and the salt is fully dissolved and salted by mechanical stirring to obtain a saturated raw material liquid; S2. The saturated raw material liquid obtained in S1 is transported to a tubular heat exchanger, and after two stages of heat exchange, is transported to a tubular evaporator, and an MVR evaporation crystallization method is adopted. After evaporation and concentration under the joint promotion of a heat source and a negative pressure environment, the liquid is sent to a forced circulation crystallizer for crystallization, wherein the low-solid content material at the top of the crystallizer is withdrawn to the evaporator for circulation and concentration, and then returned to the crystallizer, and the material is discharged from the bottom to obtain a crystal slurry; S3. The slurry obtained in S2 is separated by a centrifuge to obtain solid crystal particles and liquid, and the liquid is returned to the evaporation step; S4. The solid crystal particles obtained in S3 are transported to a ZLG vibrating fluidized bed dryer for drying and screening to obtain low sodium salt.

2. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S1, the saturated raw material solution includes, by mass percentage, 15.58±0.5% sodium chloride, 8.14±0.2% potassium chloride, and 76.28±0.5% water.

3. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S1, the reverse osmosis water is purified using an RO membrane, the inlet pressure is 1.0 MPa, and the RO water flow rate is 1-1.2 m 3 / h, concentrated water flow rate is 0.9-1.0m 3 / h.

4. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S2, the two-stage heat exchange method is: the saturated raw liquid first exchanges heat with the system evaporation condensate in the first stage, and then exchanges heat with the secondary non-condensable gas in the tube evaporator condensate gas-liquid separation tank in the second stage; the MVR evaporation crystallization process conditions are: continuous feeding, feeding rate controlled at 0.2-0.3m 3 / h, 24h continuous evaporation per day, maintain the MVR compressor frequency at 85-90%, the current at 55-60A, and the evaporation rate at 0.3-0.35m 3 / h, the evaporation temperature is controlled at 80-85℃.

5. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S2, the forced circulation crystallizer is of FC type, the vacuum degree of the crystallizer is 0.07-0.08MPa, and the circulation volume of the crystal slurry corresponding to the circulation pump is 85-90m 3 / h.

6. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S2, the continuous discharge rate at the bottom is 0.1-0.2m 3 / h.

7. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S3, the centrifuge is a horizontal centrifuge, the centrifugal frequency is 30 Hz, and the centrifugal time is 3-4 min.

8. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S4, the inlet air temperature of the fluidized bed dryer is controlled to be 120±2°C, the bed temperature is controlled to be 100±2°C, the blower frequency is controlled to be 50Hz, the induced draft fan frequency is controlled to be 40Hz, the vibration motor frequency is controlled to be 30Hz, and the conveyor frequency is controlled to be 35Hz.

9. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S4, the low sodium salt is a cubic eutectic particle, sodium chloride is used as a seed crystal, and sodium chloride and potassium chloride are epitaxially eutectic grown.

10. The method for preparing a continuous co-crystallized low sodium salt according to claim 1, characterized in that: In S4, the KCl content in the low sodium salt is 25-35%; the particle size distribution range is: the proportion of solid particles larger than 0.9 mm is ≥47%, and the proportion of solid particles larger than 0.55 mm is ≥83%.

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