Method and system for preparing molten salt grade sodium nitrate
Through multiple evaporation and crystallization processes, combined with strict temperature and pressure control, the problems of low purity of sodium nitrate and poor storage stability were solved, and molten salt-grade sodium nitrate particles were prepared.
Patent Information
- Application Number
- CN202411893543.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-20
- Publication Date
- 2025-03-07
AI Technical Summary
The sodium nitrate produced by the existing production process has low purity and poor long-term storage stability, which cannot meet the molten salt-grade product standards.
High-purity molten salt-grade sodium nitrate granules are prepared through primary and secondary concentration, crystallization, centrifugal separation, drying and granulation steps, using multiple evaporation and crystallization, combined with strict temperature and pressure control.
The preparation of high-purity sodium nitrate is achieved, complies with the quality standards of molten salt grades, and improves the long-term storage stability and compressive strength of the product.
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Figure CN119569085A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of sodium nitrate preparation technology, and in particular to a method and system for preparing molten salt-grade sodium nitrate. Background Art
[0002] Molten salt-grade sodium nitrate is currently one of the main raw materials for molten salt energy storage, and is mainly used in fields such as solar thermal power generation and thermal power plant transformation. In solar thermal power generation, molten salt is used as a heat transfer and storage medium to improve the utilization rate of solar energy, reduce power fluctuations, and promote stable output of the power grid. In the transformation of thermal power plants, molten salt heat storage equipment can transform them into energy storage peak-shaving power stations, flexibly output electricity, and improve economic benefits. In addition, molten salt energy storage can also be used for clean heating. By recovering waste heat and waste heat, it can provide industrial parks with stable and continuous high-quality heat sources such as steam and hot air. It has the advantages of strong peak-shaving capability, suitability for large-scale applications, long service life, excellent economic benefits, safety and environmental protection.
[0003] At present, the main production methods of sodium nitrate include nitric acid tail gas absorption method, neutralization method, double decomposition method, ion exchange method and sodium nitre purification method. Different from general industrial grade sodium nitrate, molten salt grade sodium nitrate is subject to the characteristics of high temperature use over 550℃, and has higher requirements for the content of chloride ions, magnesium ions and nitrite ions and other impurities that affect the corrosion of core products.
[0004] At present, most of the processes for producing sodium nitrate are industrial-grade products, which cannot meet the standards of molten salt-grade products. Therefore, developing a preparation method and system for molten salt-grade sodium nitrate is an industrial problem that urgently needs to be solved. Summary of the invention
[0005] In view of the technical problems existing in the background technology, the present invention provides a method and system for preparing molten salt grade sodium nitrate, aiming to solve the technical problems that the sodium nitrate produced by the existing production process has low purity and does not meet the molten salt grade product standard and has poor long-term storage stability.
[0006] In a first aspect, the present invention provides a method for preparing molten salt grade sodium nitrate, comprising the following steps: The sodium nitrate mother liquor is concentrated and crystallized once, and then centrifuged to obtain an industrial-grade sodium nitrate product; Dissolving an industrial-grade sodium nitrate product to obtain an industrial-grade sodium nitrate solution; The industrial-grade sodium nitrate solution is subjected to secondary concentration and secondary crystallization, followed by centrifugal separation and primary drying; The material after primary drying is granulated, secondary dried and sieved in sequence to obtain molten salt grade sodium nitrate particles; A concentration includes several evaporation processes, and the temperature and pressure of the evaporation processes decrease in sequence along the material transport direction; The secondary concentration includes several evaporation processes, and the temperature and pressure of the several evaporation processes decrease successively along the material transport direction.
[0007] In a second aspect, the present invention provides a system for preparing molten salt-grade sodium nitrate, comprising a primary concentration unit, a first crystallizer, a first centrifuge, a dissolver, a secondary concentration unit, a second crystallizer, a second centrifuge, a primary dryer, a granulator, a secondary dryer and a sieving machine connected in sequence; The primary concentration unit includes a plurality of evaporators, and the temperature and pressure of the plurality of evaporators decrease in sequence along the material transport direction; The secondary concentration unit includes a plurality of evaporators, and the temperature and pressure of the plurality of evaporators decrease in sequence along the material transport direction; The system for preparing molten salt-grade sodium nitrate is used to execute the method for preparing molten salt-grade sodium nitrate provided in the first aspect of the present invention.
[0008] Preferably, the primary concentration unit comprises a first evaporator and a second evaporator; the first evaporator is controlled at a temperature of 90-95°C and a pressure of 95-98KPa; the second evaporator is controlled at a temperature of 70-75°C and a pressure of 80-85KPa.
[0009] Preferably, the first crystallizer is controlled at a temperature of 50-55°C and a pressure of 75-80KPa; the second crystallizer is controlled at a temperature of 50-55°C and a pressure of 75-80KPa.
[0010] Preferably, the temperature of the industrial-grade sodium nitrate solution in the dissolver is 70-76° C., and the concentration of the industrial-grade sodium nitrate solution in the dissolver is 60-68 g / L.
[0011] Preferably, the secondary concentration unit comprises a first-effect evaporator, a second-effect evaporator, a third-effect evaporator and a fourth-effect evaporator; the first-effect evaporator is controlled at a temperature of 90-95°C and a pressure of 95-98KPa; the second-effect evaporator is controlled at a temperature of 80-85°C and a pressure of 90-95KPa; the third-effect evaporator is controlled at a temperature of 70-75°C and a pressure of 85-90KPa; the fourth-effect evaporator is controlled at a temperature of 60-65°C and a pressure of 80-85KPa.
[0012] In some embodiments of the present invention, the centrifuge is a two-stage pusher centrifuge for centrifugal separation, the rotation speed is 200-1100 r / min, and water can be sprayed in the centrifuge drum to wash the product again.
[0013] Preferably, the temperature of the primary dryer is 80-90°C.
[0014] Preferably, the feeding speed of the granulator is 0.5-3 m³ / h, and the feeding humidity of the granulator is 0.6%-1%.
[0015] In some embodiments of the present invention, the granulator is a double-roll granulator.
[0016] Preferably, the temperature of the secondary dryer is 80-90°C.
[0017] Preferably, the particle size of the molten salt-grade sodium nitrate particles obtained after screening by the screening machine is 5 to 10 mm.
[0018] The principle of the technical solution of the present invention is: the produced industrial-grade sodium nitrate is dissolved in desalted water, and then subjected to multi-effect evaporation, crystallization and separation to reduce the chloride content in the product to the requirement of the molten salt product.
[0019] In multiple-effect evaporation, the temperature and pressure of each effect decrease in sequence. This design helps to reduce the temperature gradient during the evaporation process. A smaller temperature gradient can reduce thermal shock and reduce the stress of crystals caused by rapid temperature changes, thereby reducing crystal breakage, maintaining the integrity of the crystals, and gradually increasing the particle size of the product during crystallization (if the temperature gradient is too large, crystals will suddenly form, and the resulting crystals will have a smaller particle size, and the centrifuge cannot separate them if the particle size is too small), which is beneficial to centrifuge separation and saves steam consumption. Granulate the molten salt-grade sodium nitrate crystals separated by centrifugation, and obtain molten salt-grade sodium nitrate particles of the target particle size by controlling the feed rate and feed humidity, which improves the strength of the sodium nitrate and is beneficial to subsequent long-term storage, transportation and use.
[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The method for preparing molten salt grade sodium nitrate provided by the present invention can produce high-purity sodium nitrate that meets the molten salt grade quality standard through multiple evaporation and crystallization, as well as strict temperature and pressure control; the sodium nitrate that meets the molten salt grade quality standard obtained through multiple evaporation and crystallization has improved strength after granulation, and can be stored for a long time to maintain stable quality.
[0021] (2) The preparation system provided by the present invention can simultaneously produce industrial-grade sodium nitrate products and molten salt-grade sodium nitrate products, and has low investment cost. There is no need to build a new set of equipment. The entire process can achieve continuous production, thereby improving production efficiency and output. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 The present invention is a schematic flow diagram of a method for preparing molten salt-grade sodium nitrate; Figure 2 The present invention is a schematic diagram of the system structure of the method for preparing the above-mentioned molten salt grade sodium nitrate; Explanation of the reference numerals: 1-primary concentration unit; 1a-first evaporator; 1b-second evaporator; 2-first crystallizer; 3-first centrifuge, 4-dissolver; 5-secondary concentration unit; 51-first effect evaporator; 52-second effect evaporator; 53-third effect evaporator; 54-fourth effect evaporator; 6-second crystallizer; 7-second centrifuge; 8-primary dryer; 9-granulator; 10-secondary dryer; 11-screening machine. DETAILED DESCRIPTION
[0023] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the protection scope of the present invention.
[0024] In the description of the embodiments of the present invention, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.
[0025] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.
[0026] See also Figure 1 In order to solve the technical problems that the sodium nitrate obtained by the existing production process has low purity and cannot meet the molten salt grade product standard and has poor long-term storage stability, the present invention provides a method for preparing molten salt grade sodium nitrate, comprising the following steps: S1. Concentrating and crystallizing the sodium nitrate mother liquor once, and obtaining an industrial-grade sodium nitrate product after centrifugal separation; the primary concentration includes several evaporation processes, and the temperature and pressure of the several evaporation processes decrease successively along the material transportation direction; S2, dissolving the industrial-grade sodium nitrate product to obtain an industrial-grade sodium nitrate solution; S3, secondary concentration and secondary crystallization of the industrial-grade sodium nitrate solution, followed by centrifugal separation and primary drying in sequence; the secondary concentration includes several evaporation processes, and the temperature and pressure of the several evaporation processes decrease in sequence along the material transport direction; S4. The material after primary drying is granulated, secondary dried and sieved in sequence to obtain molten salt grade sodium nitrate particles.
[0027] See also Figure 2 The present invention provides a system for preparing molten salt grade sodium nitrate, comprising a primary concentration unit 1, a first crystallizer 2, a first centrifuge 3, a dissolver 4, a secondary concentration unit 5, a second crystallizer 6, a second centrifuge 7, a primary dryer 8, a granulator 9, a secondary dryer 10 and a sieving machine 11 connected in sequence, Figure 2 The system structure diagram shown in the figure details the working process of the molten salt grade sodium nitrate preparation system: The sodium nitrate mother liquor is transported to a primary concentration unit 1 for primary concentration. The primary concentration unit 1 includes a first evaporator 1a and a second evaporator 1b. The second evaporator 1b is connected to the first evaporator 1a and is used to remove part of the water in the sodium nitrate mother liquor and increase the concentration of sodium nitrate in the sodium nitrate mother liquor. The concentrated sodium nitrate mother liquor is transported to a first crystallizer 2 for crystallization. When the concentration of the sodium nitrate mother liquor reaches a saturated state after concentration, sodium nitrate will precipitate from the solution in the form of crystals. The material after the primary crystallization is transported to a first centrifuge 3 for centrifugal separation to obtain an industrial-grade sodium nitrate product. The industrial-grade sodium nitrate product is transported to a dissolver 4 for dissolution with water to form an industrial-grade sodium nitrate solution, in preparation for the next step of secondary concentration and secondary crystallization. The industrial-grade sodium nitrate solution is transported to a secondary concentration unit 5. The secondary concentration unit 5 includes a first-effect evaporator 51, a second-effect evaporator 52, and a third-effect evaporator 53 connected in sequence. The evaporator 53 and the four-effect evaporator 54 are used to reduce the temperature gradient during the evaporation and crystallization process, gradually remove part of the water in the industrial-grade sodium nitrate solution, and increase the concentration of sodium nitrate in the industrial-grade sodium nitrate solution; the material after the secondary concentration is transported to the second crystallizer 6 for crystallization to precipitate sodium nitrate crystals; the material after the secondary crystallization is transported to the second centrifuge 7 for centrifugal separation, wherein the filtrate is transported to the first evaporator 1a to cycle the above working process, and the solid is transported to the primary dryer 8 for drying and removing moisture; the material after the primary drying is transported to the granulator 9 for granulation, which is used to increase the compressive strength of the sodium nitrate crystals for subsequent storage and use; after granulation, the material is transported to the secondary dryer 10 for secondary drying to ensure that the water is fully removed; the material after the secondary drying is transported to the screening machine 11 for screening, and particles of different sizes are separated to obtain molten salt-grade sodium nitrate particles of target specifications.
[0028] The components of sodium nitrate mother liquor in the following examples of the present invention are shown in Table 1: Table 1
[0029] 1. Preparation method Example 1 A method for preparing molten salt grade sodium nitrate comprises the following steps: S1, the sodium nitrate mother liquor is concentrated and crystallized once, the sodium nitrate mother liquor is first transported to the first evaporator, the temperature of the first evaporator is controlled at 95°C and the pressure is 95KPa; then it is transported to the second evaporator, the temperature of the second evaporation is controlled at 75°C and the pressure is 85KPa; then it is transported to the first crystallizer, the temperature is controlled at 55°C and the pressure is 80KPa; the crystallized material is transported to a two-stage pusher centrifuge for centrifugal separation at a speed of 800r / min, and water is sprayed in the centrifuge drum during centrifugation to wash the product again; industrial grade sodium nitrate product is obtained; S2. The industrial-grade sodium nitrate product is transported to a dissolution tank and dissolved in desalted water. The temperature of the industrial-grade sodium nitrate solution is controlled to be 75°C and the concentration of the industrial-grade sodium nitrate is 65g / L. S3, the industrial-grade sodium nitrate solution is subjected to secondary concentration and crystallization, the industrial-grade sodium nitrate solution is first transported to the first-effect evaporator, the temperature is controlled at 95°C and the pressure is 98KPa; then it is transported to the second-effect evaporator, the temperature is controlled at 85°C and the pressure is 95KPa; then it is transported to the third-effect evaporator, the temperature is controlled at 75°C and the pressure is 90KPa; then it is transported to the fourth-effect evaporator, the temperature is controlled at 65°C and the pressure is 85KPa; then it is transported to the second crystallizer, the temperature is controlled at 55°C and the pressure is 80KPa; the crystallized material is transported to a two-stage pusher centrifuge for centrifugal separation at a speed of 800r / min, and water can be sprayed in the centrifuge drum to wash the product again; the filtrate after centrifugation is pumped to the first evaporator in S1 to repeat the above steps; the solid after centrifugation is transported to a drying furnace for primary drying at a drying temperature of 90°C; S4. The solid after primary drying is transported to a double-roll granulator, the feeding speed is controlled to be 1.5m³ / h, the feed humidity is 0.8%, and secondary drying is performed after granulation at a drying temperature of 90°C. After screening, molten salt-grade sodium nitrate particles with a particle size of 5-10mm are obtained.
[0030] Example 2 A method for preparing molten salt grade sodium nitrate comprises the following steps: S1, the sodium nitrate mother liquor is concentrated and crystallized once, the sodium nitrate mother liquor is first transported to the first evaporator, the first evaporator is controlled at a temperature of 95°C and a pressure of 98KPa; then it is transported to the second evaporator, the second evaporation is controlled at a temperature of 70°C and a pressure of 82KPa; then it is transported to the first crystallizer, the temperature is controlled at 50°C and the pressure is 75KPa; the crystallized material is transported to a two-stage pusher centrifuge for centrifugal separation at a speed of 1000r / min, and water is sprayed in the centrifuge drum during centrifugation to wash the product again; industrial grade sodium nitrate product is obtained; S2. Transport the industrial-grade sodium nitrate product to a dissolution tank, use desalted water for dissolution, control the temperature of the industrial-grade sodium nitrate solution to 70°C, and the concentration of the industrial-grade sodium nitrate to 60g / L; S3, the industrial-grade sodium nitrate solution is subjected to secondary concentration and crystallization, first the industrial-grade sodium nitrate solution is transported to the first-effect evaporator, the temperature is controlled at 90°C and the pressure is 95KPa; then it is transported to the second-effect evaporator, the temperature is controlled at 80°C and the pressure is 90KPa; then it is transported to the third-effect evaporator, the temperature is controlled at 70°C and the pressure is 85KPa; then it is transported to the fourth-effect evaporator, the temperature is controlled at 60°C and the pressure is 80KPa; then it is transported to the second crystallizer, the temperature is controlled at 50°C and the pressure is 75KPa; the crystallized material is transported to a two-stage pusher centrifuge for centrifugal separation at a speed of 1000r / min, and water can be sprayed in the centrifuge drum to wash the product again; the filtrate after centrifugation is pumped to the first evaporator in S1 to repeat the above steps; the solid after centrifugation is transported to a drying furnace for primary drying at a drying temperature of 80°C; S4. The solid after primary drying is transported to a double-roll granulator, the feeding speed is controlled to be 1.5m³ / h, the feed humidity is 0.8%, and secondary drying is performed after granulation at a drying temperature of 90°C. After screening, molten salt-grade sodium nitrate particles with a particle size of 5-10mm are obtained.
[0031] Example 3 This embodiment provides a method for preparing molten salt-grade sodium nitrate, which is different from Example 1 in that: in step S4, the feeding rate is controlled to be 0.5 m³ / h; and the remaining steps are the same as in Example 1.
[0032] Example 4 This embodiment provides a method for preparing molten salt-grade sodium nitrate, which is different from Example 1 in that: in step S4, the feeding rate is controlled to be 3m³ / h; and the remaining steps are the same as in Example 1.
[0033] Example 5 This embodiment provides a method for preparing molten salt-grade sodium nitrate, which is different from Embodiment 1 in that: in step S4, the feed humidity is controlled to be 0.6%; and the remaining steps are the same as in Embodiment 1.
[0034] Example 6 This embodiment provides a method for preparing molten salt-grade sodium nitrate, which is different from Embodiment 1 in that: in step S4, the feed humidity is controlled to be 1%; and the remaining steps are the same as those in Embodiment 1.
[0035] Comparative Example 1 The present comparative example provides a method for preparing molten salt-grade sodium nitrate, which is different from Example 1 in that: Step S3 specifically comprises: conducting secondary concentration and crystallization of the industrial-grade sodium nitrate solution, firstly conveying the industrial-grade sodium nitrate solution to a first-effect evaporator, controlling the temperature to 95°C and the pressure to 98KPa; then conveying the industrial-grade sodium nitrate solution to a second-effect evaporator, controlling the temperature to 75°C and the pressure to 90KPa; then conveying the industrial-grade sodium nitrate solution to a second-effect evaporator, controlling the temperature to 75°C and the pressure to 90KPa; then conveying the industrial-grade sodium nitrate solution to a second crystallizer, controlling the temperature to 55°C and the pressure to 80KPa; conveying the crystallized material to a two-stage pusher centrifuge for centrifugal separation at a speed of 800r / min, and spraying water in the centrifuge drum to wash the product again; the filtrate after centrifugation is pumped to the first evaporator in S1 to repeat the above steps; the solid after centrifugation is conveyed to a drying furnace for primary drying at a drying temperature of 90°C; and the remaining steps are the same as in Example 1.
[0036] Comparative Example 2 This comparative example provides a production process of molten salt grade sodium nitrate, which is different from Example 1 in that step S4 is omitted and the molten salt grade sodium nitrate is not granulated.
[0037] 2. Test Method 1. Molten salt grade sodium nitrate quality inspection The molten salt grade sodium nitrate prepared in Examples 1 to 6 and Comparative Examples 1 to 2 was tested for performance according to industrial sodium nitrate GB / T4553-2016, and the results are shown in Table 2.
[0038] 2. Molten salt grade sodium nitrate strength performance test The molten salt grade sodium nitrate prepared in Examples 1 to 6 and Comparative Examples 1 to 2 was tested for performance according to GB / T4553-2016 standard, and the results are shown in Table 3.
[0039] 3. Long-term stability test of molten salt grade sodium nitrate The molten salt grade sodium nitrate prepared in Examples 1-6 and Comparative Examples 1-2 was stored for 6 months at a temperature of 10-30° C. and a humidity of 20%-40%. The quality test was performed on the sodium nitrate. The results are shown in Table 4.
[0040] III. Analysis of test results of various embodiments and comparative examples 1. Analysis of quality test results of molten salt grade sodium nitrate The quality test results of the molten salt grade sodium nitrate prepared in Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 2.
[0041] Table 2
[0042] After testing, the molten salt grade sodium nitrate prepared in Examples 1 to 6 of the present invention all meet the standards of molten salt grade. In Comparative Example 1, only two-effect evaporation was performed during the secondary concentration and crystallization, and the residual chloride was still relatively large and was not fully removed.
[0043] 2. Test results of strength performance of molten salt grade sodium nitrate The strength performance test results of the molten salt grade sodium nitrate prepared in Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 3.
[0044] Table 3
[0045] The results in Table 3 show that the molten salt-grade sodium nitrate particles prepared in Examples 1 to 6 of the present invention have excellent compressive properties, which can reach 200N; Comparative Example 2 was not granulated, and the compressive properties were significantly lower than those in Example 1. Comparison of the results of Examples 3 to 6 with those of Example 1 shows that during the granulation process, the feed humidity and feed speed have a significant impact on the formation and quality of the particles. If the humidity is too high, the internal structure of the particles will become loose, and such a structure will be more easily broken when subjected to external force, so the compressive strength of the particles will be reduced; if the feed speed is too fast, the particles may not have enough time to be fully compacted and solidified during the molding process, thereby affecting the density and structural integrity of the particles and reducing their compressive strength.
[0046] 3. Long-term stability test results of molten salt grade sodium nitrate The results of quality testing of the molten salt-grade sodium nitrate prepared in Examples 1 to 6 and Comparative Examples 1 to 2 after being stored for 6 months in an environment of temperature 10 to 30° C. and humidity 20% to 40% are shown in Table 4.
[0047] Table 4
[0048] After testing, the molten salt grade sodium nitrate prepared in Examples 1 to 6 of the present invention still meets the molten salt grade standard in quality inspection after being stored in an environment of temperature 10 to 30° C. and humidity 20% to 40% for 6 months, and has good long-term stability.
[0049] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the main purpose of the present invention, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present invention.
Claims
1. A method for preparing molten salt grade sodium nitrate, characterized in that: The following steps are involved: The sodium nitrate mother liquor is concentrated and crystallized once, and then centrifuged to obtain an industrial-grade sodium nitrate product; Dissolving an industrial-grade sodium nitrate product to obtain an industrial-grade sodium nitrate solution; The industrial-grade sodium nitrate solution is subjected to secondary concentration and secondary crystallization, followed by centrifugal separation and primary drying; The material after primary drying is granulated, secondary dried and sieved in sequence to obtain molten salt grade sodium nitrate particles; The primary concentration includes several evaporation processes, and the temperature and pressure of the several evaporation processes decrease in sequence along the material transport direction; The secondary concentration includes several evaporation processes, and the temperature and pressure of the several evaporation processes decrease in sequence along the material transport direction.
2. A system for preparing molten salt grade sodium nitrate, characterized in that: It comprises a primary concentration unit, a first crystallizer, a first centrifuge, a dissolver, a secondary concentration unit, a second crystallizer, a second centrifuge, a primary dryer, a granulator, a secondary dryer and a sieving machine which are connected in sequence; The primary concentration unit comprises a plurality of evaporators, and the temperature and pressure of the plurality of evaporators decrease in sequence along the material transport direction; The secondary concentration unit comprises a plurality of evaporators, and the temperature and pressure of the plurality of evaporators decrease in sequence along the material transport direction; The system for preparing molten salt-grade sodium nitrate is used to execute the method for preparing molten salt-grade sodium nitrate according to claim 1.
3. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The primary concentration unit includes a first evaporator and a second evaporator; the first evaporator is controlled at a temperature of 90-95°C and a pressure of 95-98KPa; the second evaporator is controlled at a temperature of 70-75°C and a pressure of 80-85KPa.
4. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The first crystallizer is controlled at a temperature of 50-55°C and a pressure of 75-80KPa; the second crystallizer is controlled at a temperature of 50-55°C and a pressure of 75-80KPa.
5. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The temperature of the industrial-grade sodium nitrate solution in the dissolver is 70-76° C., and the concentration of the industrial-grade sodium nitrate solution in the dissolver is 60-68 g / L.
6. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The secondary concentration unit includes a first-effect evaporator, a second-effect evaporator, a third-effect evaporator and a fourth-effect evaporator; the first-effect evaporator is controlled at a temperature of 90-95°C and a pressure of 95-98KPa; the second-effect evaporator is controlled at a temperature of 80-85°C and a pressure of 90-95KPa; the third-effect evaporator is controlled at a temperature of 70-75°C and a pressure of 85-90KPa; the fourth-effect evaporator is controlled at a temperature of 60-65°C and a pressure of 80-85KPa.
7. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The temperature of the primary dryer is 80-90°C.
8. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The feeding speed of the granulator is 0.5-3 m³ / h, and the feeding humidity of the granulator is 0.6%-1%.
9. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The temperature of the secondary dryer is 80-90°C.
10. A system for preparing molten salt-grade sodium nitrate according to claim 2, characterized in that: The particle size of the molten salt-grade sodium nitrate particles obtained after screening by the screening machine is 5-10 mm.