A device for re-salting brine after nitrate production

Abstract

This invention discloses a device for re-extracting salt from brine after nitrate production, comprising a heat exchanger with a steam inlet pipe on the heat exchanger and a brine inlet pipe at the bottom of the heat exchanger. A separator is connected to the side wall of the heat exchanger via a connecting pipe for conveying heated brine to the separator. A discharge pipe is located at the top of the separator, and an integrated washing salt leg is located at the bottom of the separator. The integrated washing salt leg is divided into a crystallization transition zone, a primary washing zone, a secondary fine washing zone, and a salt slurry collection zone from top to bottom. This invention abandons the traditional segmented process, directly integrating the washing function into the integrated washing salt leg of the separator. It eliminates the need for additional external washing equipment and salt slurry transfer links, achieving integrated operation of in-situ crystallization of salt crystals, simultaneous in-situ washing, and direct discharge of high-purity salt slurry. This avoids agglomeration, wear, and secondary pollution during salt slurry transfer, while also eliminating the problem of mother liquor clumping on the salt crystal surface caused by transport delays, thus improving the thoroughness of salt crystal washing.

Description

Technical Field

[0001] This invention belongs to the technical field of salt chemical equipment, specifically, it relates to a device for re-extracting salt from brine after nitrate production. Background Technology

[0002] In the salt chemical production process, the brine after nitrate production still contains a large amount of sodium chloride (NaCl), which has high recovery value. Reprocessing it for salt extraction can improve salt resource utilization and reduce wastewater discharge, aligning with the industry's trend towards energy conservation and environmental protection. Currently, the conventional process for reprocessing brine after nitrate production mostly adopts a segmented operation mode of "evaporation and crystallization → external delivery of salt slurry → external washing machine." While this mode can achieve salt crystal recovery, it suffers from many common problems that are difficult to solve in practice, severely restricting salt extraction efficiency, salt quality, and production economics.

[0003] The core defects of the existing segmented salt extraction process and supporting equipment are as follows: Firstly, the process is disconnected. Crystallization and washing are separated into two independent units. The salt slurry (containing a large amount of high-nitrate mother liquor) discharged from the salt leg of the separator needs to be transferred to an external washing machine through a transfer pump and pipeline. During the transfer process, the salt crystals are prone to agglomeration and wear, and will carry air and impurities, resulting in secondary contamination of the salt crystals and affecting the purity of the salt. Secondly, energy consumption and water waste are prominent. The transfer of salt slurry requires additional pumping energy, and the external washing device needs to provide fresh washing water separately. At the same time, the overflow liquid after washing needs to be treated separately. The overall energy consumption and water consumption of the system are relatively high. Third, the equipment occupies a large area. The external washing device (vertical / horizontal) requires a separate site, and there are many supporting pipes and valves, making the equipment layout complex. For small and medium-sized salt extraction devices, the site constraints are very obvious. Fourth, insufficient washing of salt crystals and a lag in the transport of salt slurry from the crystallizer to the washing machine cause the high-nitrate mother liquor on the surface of the salt crystals to dry and clump, making it difficult to remove completely during subsequent washing. This limits the improvement of salt purity and makes it difficult to meet the production requirements of high-purity salt products. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a device for re-extracting salt from brine after nitrate production.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: a brine re-salt extraction device after nitrate production, comprising a heat exchanger, a steam inlet pipe for introducing heating steam into the heat exchanger; a brine inlet pipe at the bottom of the heat exchanger for introducing brine to be treated into the heat exchanger; a separator connected to the side wall of the heat exchanger via a connecting pipe for conveying the heated brine to the separator, which performs gas-liquid separation on the brine; a discharge pipe at the top of the separator for discharging the separated gas; an integrated washing salt leg at the bottom of the separator, the integrated washing salt leg having no internal partitions and being divided from top to bottom into a crystallization transition zone, a primary washing zone, a secondary refining zone, and a salt slurry collection zone, each zone being used for graded washing of the salt slurry; and a salt slurry outlet pipe at the bottom of the salt slurry collection zone for discharging the washed salt slurry.

[0006] Preferably, the crystallization transition zone has a gradually tapered frustum structure that is wider at the top and narrower at the bottom, with a cone angle of 30°-45°; the inner wall of the crystallization transition zone is provided with annular guide plates at equal intervals, which are used to guide the salt crystals; the annular guide plates are provided with through holes at equal intervals, which are used for the flow of salt crystals and brine.

[0007] Preferably, the annular guide plate is horizontally arranged on the inner wall of the crystallization transition zone, and the end of the annular guide plate is inclined downward toward the center of the integrated washing salt leg to guide the salt crystals to flow downward.

[0008] Preferably, the primary washing zone is a cylindrical cavity, and an annular pipe is provided on the inner wall of the primary washing zone; washing water spray nozzles are provided at equal intervals below the annular pipe, and the washing water spray nozzles are used to spray washing water, with the spray angle of the washing water spray nozzles being 45° downward; a spray pipe is provided at one end of the annular pipe, and the spray pipe is used to transport washing water to the annular pipe.

[0009] Preferably, the secondary fine washing zone has a reverse truncated cone structure that is narrow at the bottom and wide at the top, with a cone angle of 25°-35°; a water distributor is provided at the bottom of the secondary fine washing zone to evenly distribute the washing water; a washing water inlet pipe is provided at one end of the water distributor to deliver washing water to the water distributor.

[0010] Preferably, a condensate outlet pipe is provided on one side of the heat exchanger, which is used to discharge the condensate in the heat exchanger; the condensate outlet pipe is connected to the spray pipe and the rinsing water inlet pipe respectively through a variable frequency pump, which is used to transport the condensate to the spray pipe and the rinsing water inlet pipe respectively.

[0011] Preferably, the integrated washing salt leg is equipped with an overflow pipe on the side wall below the primary washing zone and above the secondary fine washing zone. The overflow pipe is used to discharge the brine after washing. A filter screen is installed inside the overflow pipe to filter salt crystals in the brine. The overflow pipe is connected to the brine inlet pipe through a circulation pump, which is used to transport the overflowed brine back to the brine inlet pipe.

[0012] Preferably, a purge pipe is inclinedly installed at one end of the overflow pipe near the integrated washing salt leg. The purge pipe is used to purge gas into the overflow pipe. A one-way valve is installed on the purge pipe to prevent brine backflow.

[0013] Compared with the prior art, the advantages of the present invention include: (1) Abandoning the traditional segmented process, the washing function is directly integrated into the integrated washing salt leg of the separator, eliminating the need for additional external washing equipment and salt slurry transfer links, realizing the integrated operation of "salt crystal in-situ crystallization → synchronous in-situ washing → direct discharge of high-purity salt slurry", avoiding agglomeration, wear and secondary pollution during the salt slurry transfer process, while eliminating the problem of mother liquor clumping on the salt crystal surface caused by the lag in transportation, and improving the fullness of salt crystal washing; (2) The condensate generated by the heat exchanger is used as the washing water. There is no need to connect fresh water from outside. The water is accurately delivered to the spray pipe and the washing water inlet pipe through the frequency conversion pump, so as to realize the recycling of the washing water. At the same time, the pumping energy consumption of salt slurry transfer is eliminated, the operating energy consumption of external washing equipment is reduced, and the overall energy consumption and water consumption of the system are greatly reduced, which meets the requirements of energy conservation and environmental protection. (3) The integrated washing salt leg integrates the functions of crystallization transition, graded washing and salt slurry collection into one unit. There is no need to set up a separate external washing device, which reduces the space occupied by the equipment, simplifies the equipment layout, and is especially suitable for small and medium-sized salt production lines with limited space, thus reducing equipment investment costs. (4) The integrated washing salt leg is set up with a crystallization transition zone, a primary washing zone and a secondary fine washing zone from top to bottom to achieve graded washing of salt crystals. The primary washing washes away most of the high-nitrate mother liquor and impurities on the surface, and the secondary fine washing thoroughly removes the salt crystal gaps and residual nitrate ions and impurities on the surface. Combined with the filtering effect of the filter screen, the purity of the salt is improved and the quality of the salt is ensured to be stable. (5) The annular guide plate in the crystallization transition zone can slow down the salt crystal settling speed, avoid salt crystal breakage and agglomeration, and lay the foundation for subsequent washing; the overflow pipe is equipped with a purge pipe and a one-way valve, which can effectively prevent overflow pipe blockage and prevent brine backflow; the integrated washing salt leg has no internal partitions, which reduces salt crystal adhesion and scaling, and ensures long-term stable operation of the device. (6) After rinsing, the overflow brine is filtered through a filter screen and then pumped back to the brine inlet pipe by a circulation pump. It then re-enters the heat exchanger for heating, thus realizing the recycling of brine and reducing resource waste. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of a brine salt extraction device after nitrate production according to the present invention; Figure 2 This is a schematic diagram of the structure of the heat exchanger in a brine re-salt extraction device after nitrate production according to the present invention; Figure 3 This is a schematic diagram of the integrated washing salt leg in a brine re-salt extraction device after nitrate production according to the present invention; Figure 4 This is a schematic diagram of the internal structure of the integrated washing salt leg in a brine re-salting device after nitrate production according to the present invention. Figure 5 This is a schematic diagram of the overflow pipe in a brine re-salt extraction device after nitrate production according to the present invention.

[0016] Figure label: 11. Heat exchanger; 12. Separator; 13. Brine inlet pipe; 14. Steam inlet pipe; 15. Condensate outlet pipe; 16. Connecting pipe; 17. Discharge pipe; 18. Integrated washing salt leg; 19. Salt slurry outlet pipe; 21. Circulating pump; 22. Overflow pipe; 23. Filter screen; 24. Purge pipe; 25. One-way valve; 31. Crystallization transition zone; 32. Annular guide plate; 33. Through hole; 41. Primary washing zone; 42. Spray pipe; 43. Annular pipe; 44. Washing water spray nozzle; 51. Secondary fine washing zone; 52. Washing water inlet pipe; 53. Water distributor. Detailed Implementation

[0017] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The technical solution, its implementation process, and principles will be further explained below with reference to the accompanying drawings and specific implementation examples in the embodiments of this application.

[0018] It should be noted that the embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, the present invention covers any substitutions, modifications, equivalent methods and solutions made on the spirit, principles and scope of the present invention as defined by the claims. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In the description of this application, the terms "first," "second," "third," and similar words do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "a" or "one," and similar words, do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including," and similar words, mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including," and their equivalents, but do not exclude other elements or objects. The terms "connected" or "linked," and similar words, are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0020] In the description of this application, the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing this application and for simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, when using positional terms such as "both sides," "outer side," and "upper and lower," it should be understood that they are used only for ease of understanding and description, taking into account that the structure may be oriented to other positions.

[0021] In the description of this application, unless otherwise expressly specified and limited, the technical or scientific terms used shall have the ordinary meaning understood by a person with ordinary skills in the art to which this application pertains. Terms such as “installation,” “connection,” and “joining” shall be interpreted broadly, for example, as fixed connection, detachable connection, mating connection, or integral connection. For a person skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0022] The present invention aims to introduce and explain the structural composition of a brine re-salt extraction device after nitrate production and the coordination relationship between the various components. Unless otherwise specified, the dimensions, materials, and manufacturing processes of the various components in the brine re-salt extraction device after nitrate production in the present invention embodiments can be selected according to specific circumstances, and no special limitations or explanations are made here.

[0023] Furthermore, to provide the public with a better understanding of the present invention, certain specific details are described in detail in the following description of the invention. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0024] Please see Figures 1-5A device for re-extracting salt from nitrate-producing brine includes a heat exchanger 11 and supporting pipelines. The heat exchanger 11 can be a shell-and-tube heat exchanger made of 316L stainless steel, which has good corrosion resistance and heat exchange efficiency, and is suitable for the corrosive conditions of the nitrate-producing brine. A steam inlet pipe 14 is provided at the top of the heat exchanger 11. The steam inlet pipe 14 is made of seamless steel pipe and is used to introduce saturated heating steam (temperature 100-120℃) into the heat exchanger 11 to provide heat for heating the brine. A brine inlet pipe 13 is provided at the bottom of the heat exchanger 11. The brine inlet pipe 13 is used to introduce pretreated nitrate-producing brine into the heat exchanger 11 (pretreatment removes suspended impurities to avoid clogging of pipelines and equipment). The brine exchanges heat with the heating steam in the heat exchanger 11, and the temperature rises to 50-55℃ (matching the sodium chloride crystallization temperature to avoid sodium sulfate crystallization). A condensate outlet pipe 15 is provided on one side of the heat exchanger 11. The condensate outlet pipe 15 is used to discharge the condensate after the heating steam in the heat exchanger 11 is condensed. The condensate temperature is maintained at 80-90℃ and can be recycled as washing water to realize the recovery of water resources and waste heat. In order to ensure that the washing water temperature matches the internal temperature (50-55℃) of the integrated washing salt leg 18 and avoid the salt crystals from dissolving or the stability of the mother liquor caused by high temperature washing water, a small cooling device (such as a coil cooling) can be added between the condensate outlet pipe 15 and the spray pipe 42 and the washing water inlet pipe 52. The device lowers the temperature of the condensate to 50-55℃ before it is delivered. The condensate outlet pipe 15 is connected to the spray pipe 42 and the washing water inlet pipe 52 via a variable frequency pump. The variable frequency pump is a corrosion-resistant centrifugal pump, and the flow rate can be automatically adjusted according to the amount of salt crystal sedimentation (this can be achieved by setting a salt crystal sedimentation sensor in the crystallization transition zone 31 to detect the salt crystal sedimentation speed in real time, and feeding the signal to the variable frequency pump controller to dynamically adjust the flow rate). This is a relatively mature technology, which will not be elaborated here. This ensures that the amount of washing water supplied matches the amount of salt crystals, avoiding waste of washing water or insufficient washing.

[0025] Please see Figures 1-5 The separator 12 and the discharge pipe 17 are connected. The separator 12 is a vertical cylindrical structure made of 316L stainless steel and is used for gas-liquid separation of heated brine. The side wall of the heat exchanger 11 is connected to the middle of the separator 12 through the connecting pipe 16. The connecting pipe 16 is inclined (30°) to facilitate the smooth flow of heated brine (containing a small amount of water vapor) into the separator 12. The separator 12 is equipped with baffles (not shown in the figure) to slow down the brine flow rate and fully separate the water vapor from the brine. The separated water vapor (containing a small amount of light impurities) is discharged from the discharge pipe 17 at the top of the separator 12. The discharge pipe 17 can be connected to a tail gas treatment device (not shown in the figure) to prevent the direct emission of waste gas and environmental pollution. The bottom end of the separator 12 is fixedly connected to the integrated washing salt leg 18. It is an integrated design, or it can be connected by a flange seal to ensure that there is no leakage at the connection. The separated brine (containing supersaturated sodium chloride) flows into the integrated washing salt leg 18 under the action of gravity for in-situ crystallization and graded washing, so as to achieve the separation and purification of salt crystals and mother liquor.

[0026] Please see Figures 1-5 The integrated salt washing leg 18 is made of 316L stainless steel and is integrally molded. There are no partitions or splices inside, which avoids leakage and salt crystal accumulation and blockage. From top to bottom, it is divided into a crystallization transition zone 31, a primary washing zone 41, a secondary fine washing zone 51 and a salt slurry collection zone. Each zone works together to achieve in-situ crystallization, graded washing and collection of salt crystals, without the need for external washing equipment. Crystallization transition zone 31: Located on the upper part of the integrated washing salt leg 18 and connected to the bottom of the separator 12, it has a gradually tapered truncated cone structure that is wider at the top and narrower at the bottom, with a cone angle between 30° and 45°. This structure can slow down the settling speed of salt crystals and prevent them from breaking due to rapid impact with the bottom. The inner wall of the crystallization transition zone 31 is provided with 3-4 ring-shaped guide plates 32 at equal intervals, with a spacing between 15-20cm. The ring-shaped guide plates 32 are horizontally arranged on the inner wall of the crystallization transition zone 31, and the end of the ring-shaped guide plates 32 facing the center of the integrated washing salt leg 18 is inclined downward (inclination angle 10°) to guide the salt crystals to flow smoothly downward and to make the salt crystals evenly distributed, preparing for subsequent washing. The ring-shaped guide plates 32 are provided with through holes 33 with a diameter between 5-8mm at equal intervals. The through holes 33 are used for the flow of salt crystals and brine, allowing a small amount of mother liquor to pass through, reducing the entrainment of salt crystals and mother liquor, and improving the washing effect of subsequent washing.

[0027] Primary washing zone 41: Located below the crystallization transition zone 31, it is a cylindrical cavity and serves as the core washing section for preliminary washing of the settled salt crystals. An annular pipe 43 is fixedly installed on the inner wall of the primary washing zone 41. The annular pipe 43 is made of stainless steel. 6-8 washing water spray nozzles 44 (circularly distributed) are equidistantly arranged below the annular pipe 43. The spray angle of the washing water spray nozzles 44 is 45° downwards, and the spray velocity is adjustable (0.8-1.2m / s) to ensure that the washing water evenly covers the entire cavity and does not wash away qualified large salt crystals (only rinsing the surface mother liquor and small impurities). A spray pipe 42 is installed at one end of the annular pipe 43. The spray pipe 42 is connected to a variable frequency pump on the condensate outlet pipe 15 to deliver condensate (washing water) to the annular pipe 43, realizing the recycling of the washing water.

[0028] Secondary fine washing zone 51: Located below the primary washing zone 41, it has a reverse truncated cone structure that is narrow at the bottom and wide at the top, with a cone angle between 25° and 35°. This reverse truncated cone structure can slow down the rising speed of the washing water, prolong the contact time between salt crystals and washing water (contact time ≥30s), and improve the deep washing effect. At the same time, it can make salt crystals settle more easily into the salt slurry collection area under the action of gravity, avoiding loss with the overflow liquid. The bottom of the secondary fine washing zone 51 is equipped with an annular water distributor 53. The water distributor 53 adopts a microporous water distribution structure with a water distribution uniformity of ≥95%, which is finer than the washing water spray nozzle 44. It can make the washing water sprayed evenly upward, forming a countercurrent fine washing effect (salt crystals sink downward and washing water flows upward). One end of the water distributor 53 is equipped with a washing water inlet pipe 52, which is connected to the variable frequency pump on the condensate outlet pipe 15 to deliver condensate (washing water) to the water distributor 53.

[0029] Salt slurry collection area: Located at the bottom of the integrated washing salt leg 18, it has a straight cylindrical structure and is used to collect high-purity salt crystals after two-stage washing to form salt slurry (salt crystals + a small amount of clean mother liquor). The bottom of the salt slurry collection area is equipped with a salt slurry outlet pipe 19, which can be directly connected to the centrifuge feed pipe to send the washed salt slurry directly into the centrifuge for dehydration and drying to obtain finished salt. There is no need for intermediate transfer links, thus avoiding secondary contamination of salt crystals.

[0030] Please see Figures 1-5 The overflow circulation component and purging device, the integrated washing salt leg 18, is located on the side wall below the primary washing zone 41 and above the secondary fine washing zone 51, with an overflow pipe 22. The overflow pipe 22 is used to discharge the nitrate overflow liquid after washing (washing water + high-nitrate mother liquor flushed down + fine impurities). The overflow pipe 22 is equipped with a filter screen 23, which is made of stainless steel, to filter salt crystals in the brine, prevent salt crystals from being lost with the overflow liquid, and improve the salt recovery rate. The overflow pipe 22 is connected to the brine inlet pipe 13 through the circulation pump 21. The circulation pump 21 is a corrosion-resistant centrifugal pump, which is used to transport the filtered overflow brine back to the brine inlet pipe 13 and re-enter the heat exchanger 11 for heating treatment, realizing a closed-loop circulation of brine and washing water, and improving resource utilization. An overflow pipe 22 is inclined at one end near the integrated washing salt leg 18 and a purge pipe 24 is provided. The purge pipe 24 is inclined at an angle of 45° and is used to purge compressed air (pressure 0.3-0.5MPa) into the overflow pipe 22 to prevent the overflow pipe 22 from being blocked by salt crystals. A one-way valve 25 is provided on the purge pipe 24. The one-way valve 25 is made of corrosion-resistant material and is used to prevent the brine in the overflow pipe 22 from flowing back into the purge pipe 24 to ensure the normal operation of the purging device.

[0031] Work process Preliminary preparation and equipment commissioning: First, check the installation of each component to ensure that the connections of heat exchanger 11, separator 12, and integrated washing salt leg 18 are reliable and leak-free; check the operating status of variable frequency pump and circulating pump 21 to ensure smooth operation; check the cleanliness of filter screen 23 and fine screen to avoid clogging; adjust the flow parameters of variable frequency pump to ensure that the washing water supply matches the subsequent salt crystal sedimentation; adjust the internal temperature of heat exchanger 11, separator 12, and integrated washing salt leg 18 to 50-55℃, which is the optimal crystallization temperature for sodium chloride and can also inhibit the crystallization of sodium sulfate (the crystallization temperature of sodium sulfate is usually below 30℃, and it can remain dissolved in the mother liquor at 50-55℃), ensuring washing effect and salt crystal quality; adjust the purging pressure of purge pipe 24 to ensure it reaches 0.3-0.5MPa, and check the sealing of one-way valve 25 to prevent brine backflow; Preliminary preparation and equipment commissioning: First, check the installation of each component to ensure that the connections of heat exchanger 11, separator 12, and integrated washing salt leg 18 are reliable and that there are no leaks in the pipelines; check the operating status of the variable frequency pump and circulating pump 21 to ensure smooth operation; check the cleanliness of the filter screen 23 and fine screen to avoid clogging; adjust the flow parameters of the variable frequency pump to ensure that the washing water supply matches the subsequent salt crystal settling amount; adjust the internal temperature of heat exchanger 11, separator 12, and integrated washing salt leg 18 to 50-55℃ to match the sodium chloride crystallization temperature, avoid sodium sulfate crystallization, and ensure washing effect and salt crystal quality; Brine heating and gas-liquid separation: The pretreated brine after nitrate production (with suspended impurities removed) is introduced into the heat exchanger 11 through the brine inlet pipe 13. At the same time, saturated heating steam is introduced into the heat exchanger 11 through the steam inlet pipe 14. The brine and the heating steam exchange heat in the heat exchanger 11, and the temperature rises to 50-55℃. At this time, the sodium chloride in the brine reaches a supersaturated state, which prepares for subsequent crystallization. The heated brine (containing a small amount of water vapor) flows into the separator 12 through the connecting pipe 16. Under the action of the baffle plate, the water vapor and the brine are fully separated. The separated water vapor is discharged through the discharge pipe 17 at the top of the separator 12 and enters the tail gas treatment device. The separated supersaturated brine (containing unprecipitated sodium chloride) flows into the integrated washing salt leg 18 at the bottom of the separator 12 under the action of gravity, and the in-situ crystallization and washing operation begins. In-situ crystallization and graded washing: Supersaturated brine enters the crystallization transition zone 31 of the integrated washing salt leg 18. Sodium chloride in the brine gradually precipitates into fine salt crystals, which sink downwards under the action of gravity. The annular guide plate 32 of the crystallization transition zone 31 slows down the settling speed of the salt crystals, preventing them from breaking and agglomerating. At the same time, it guides the salt crystals to be evenly distributed. A small amount of mother liquor flows downwards through the through holes 33 on the annular guide plate 32, reducing the entrainment of salt crystals with mother liquor and laying the foundation for subsequent washing, thus realizing in-situ crystallization of salt crystals. The salt crystals continue to settle downwards and enter the primary washing zone 41. At this time, the variable frequency pump delivers the condensate (washing water) generated by the heat exchanger 11 to the spray pipe 42. The spray pipe 42 guides the washing water into the annular pipe 43, and sprays it evenly downwards at a 45° angle through the washing water spray nozzle 44 below the annular pipe 43. The washing water washes the surface of the salt crystals at a flow rate of 0.8-1.2 m / s, washing away most of the high-nitrate mother liquor and fine impurities attached to the surface of the salt crystals, thus achieving the initial washing of the salt crystals. The nitrate mother liquor and fine impurities after washing flow downwards with the washing water and enter the secondary fine washing zone 51. After primary washing, the salt crystals continue to settle into the secondary fine washing zone 51. At the same time, the variable frequency pump delivers condensate (cooled to 50-55℃) to the washing water inlet pipe 52. The washing water inlet pipe 52 guides the washing water into the water distributor 53. The water distributor 53 sprays the washing water upward evenly in a micro-porous water distribution manner, forming a counter-current fine washing effect (salt crystals settle downward and washing water flows upward), prolonging the contact time between the salt crystals and the washing water (≥30s), thoroughly removing residual nitrate ions and impurities from the gaps between the salt crystals and on the surface. Meanwhile, the fine mesh screen in the secondary fine washing zone 51 traps large qualified salt crystals, while small impurities and excess washing water pass through the screen holes and merge with the nitrate-containing mother liquor flowing down after primary washing to form an overflow liquid, achieving deep fine washing and grading of the salt crystals. Salt slurry collection and discharge: After two-stage in-situ washing, the high-purity salt crystals continue to settle down into the salt slurry collection area, where they aggregate to form salt slurry (salt crystals + a small amount of clean mother liquor). The salt slurry is then sent directly to a centrifuge for dehydration and drying through the salt slurry outlet pipe 19 at the bottom of the salt slurry collection area to obtain finished salt. No intermediate transfer links are required, which avoids salt crystal agglomeration, wear and secondary pollution, and improves salt quality and production efficiency. Overflow circulation and anti-clogging maintenance: The overflow liquid (containing nitrate mother liquor, fine impurities, and excess washing water) generated in the secondary fine washing zone 51 is discharged through the overflow pipe 22 on the side wall of the integrated washing salt leg 18. The filter screen 23 in the overflow pipe 22 filters out the salt crystals in the overflow liquid to prevent salt crystal loss. The filtered overflow liquid is sent back to the brine inlet pipe 13 by the circulation pump 21 and re-enters the heat exchanger 11 for heating treatment, realizing a closed-loop circulation of brine and washing water, improving resource utilization, and reducing waste of water and salt resources. During operation, compressed air is periodically blown into the overflow pipe 22 through the purge pipe 24 to remove salt crystals adhering to the inner wall of the overflow pipe 22 using air pressure, preventing the overflow pipe 22 from becoming blocked; the one-way valve 25 effectively prevents brine from flowing back into the purge pipe 24, ensuring the normal operation of the purge device; all the condensate produced by the heat exchanger 11 is recycled as washing water, eliminating the need for external fresh water and significantly reducing water consumption and operating costs.

[0032] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A device for re-extracting salt from brine after nitrate production, comprising a heat exchanger (11), wherein a steam inlet pipe (14) is provided on the heat exchanger (11) for introducing heating steam into the heat exchanger (11); a brine inlet pipe (13) is provided at the bottom end of the heat exchanger (11) for introducing brine to be treated into the heat exchanger (11); a separator (12) is provided on the side wall of the heat exchanger (11) through a connecting pipe (16), wherein the connecting pipe (16) is used to transport the heated brine to the separator (12), and the separator (12) is used to perform gas-liquid separation of the brine; a discharge pipe (17) is provided at the top end of the separator (12), wherein the discharge pipe (17) is used to discharge the separated gas; characterized in that: The separator (12) is provided with an integrated washing salt leg (18) at the bottom. The integrated washing salt leg (18) has no partitions inside and is divided into a crystallization transition zone (31), a primary washing zone (41), a secondary fine washing zone (51), and a salt slurry collection zone from top to bottom. Each zone is used to grade and wash the salt slurry. The salt slurry collection zone is provided with a salt slurry outlet pipe (19) at the bottom. The salt slurry outlet pipe (19) is used to discharge the washed salt slurry.

2. The brine extraction device after nitrate production according to claim 1, characterized in that: The crystallization transition zone (31) is a gradually tapered frustum structure that is wider at the top and narrower at the bottom, with a cone angle of 30°-45°. The inner wall of the crystallization transition zone (31) is provided with annular guide plates (32) at equal intervals, which are used to guide the flow of salt crystals. The annular guide plates (32) are provided with through holes (33) at equal intervals, which are used for the flow of salt crystals and brine.

3. The brine salt extraction device after nitrate production according to claim 2, characterized in that: The annular guide plate (32) is horizontally arranged on the inner wall of the crystallization transition zone (31). The annular guide plate (32) is inclined downward at one end toward the center of the integrated washing salt leg (18) to guide the salt crystals to flow downward.

4. A brine extraction device for nitrate production according to claim 3, characterized in that: The primary washing zone (41) is a cylindrical cavity, and an annular pipe (43) is provided on the inner wall of the primary washing zone (41); washing water spray nozzles (44) are provided at equal intervals below the annular pipe (43), and the washing water spray nozzles (44) are used to spray washing water, and the spray angle of the washing water spray nozzles (44) is 45° downward; a spray pipe (42) is provided at one end of the annular pipe (43), and the spray pipe (42) is used to transport washing water to the annular pipe (43).

5. A brine extraction device for nitrate production according to claim 4, characterized in that: The secondary fine washing zone (51) is a reverse truncated cone structure that is narrow at the bottom and wide at the top, with a cone angle of 25°-35°. A water distributor (53) is provided at the bottom of the secondary fine washing zone (51), which is used to evenly distribute the washing water. A washing water inlet pipe (52) is provided at one end of the water distributor (53), which is used to deliver washing water to the water distributor (53).

6. The brine re-salt extraction device after nitrate production according to claim 5, characterized in that: A condensate outlet pipe (15) is provided on one side of the heat exchanger (11). The condensate outlet pipe (15) is used to discharge the condensate in the heat exchanger (11). The condensate outlet pipe (15) is connected to the spray pipe (42) and the washing water inlet pipe (52) respectively through a variable frequency pump. The variable frequency pump is used to transport the condensate and deliver the condensate to the spray pipe (42) and the washing water inlet pipe (52) respectively.

7. A brine re-salt extraction device after nitrate production according to claim 1 or 6, characterized in that: The integrated washing salt leg (18) is provided with an overflow pipe (22) on the side wall below the primary washing area (41) and above the secondary fine washing area (51). The overflow pipe (22) is used to discharge the brine after washing. A filter screen (23) is provided inside the overflow pipe (22). The filter screen (23) is used to filter the salt crystals in the brine. The overflow pipe (22) is connected to the brine inlet pipe (13) through a circulation pump (21). The circulation pump (21) is used to transport the overflow brine back to the brine inlet pipe (13).

8. A brine extraction device for nitrate production according to claim 7, characterized in that: The overflow pipe (22) is inclined at one end near the integrated washing salt leg (18) and a purge pipe (24) is provided. The purge pipe (24) is used to purge gas into the overflow pipe (22). A one-way valve (25) is provided on the purge pipe (24) to prevent brine backflow.

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