A method for producing industrial salt based on multi-stage purification of high-nitrate brine

Abstract

The present application belongs to the technical field of comprehensive production of industrial salt and nitrate, and particularly relates to a method for producing industrial salt based on multi-stage purification of high-nitrate type brine. In the prior art, there is a problem that high-nitrate liquid is produced after the production of industrial salt using high-nitrate type raw brine as raw material, and the high-nitrate liquid is directly treated as waste liquid, resulting in serious resource waste and energy loss. In view of the above problem, the present application provides a method for producing industrial salt based on multi-stage purification of high-nitrate type brine, which reuses the high-nitrate liquid produced by the industrial salt production system to the industrial salt production system after treatment by a bromine removal system, greatly improving the resource utilization rate and economic benefit. In the process of operation, the heat of boiler steam is used to supply heat to the industrial salt production system, the bromine removal system and the nitrate production system, a multi-level and closed-loop heat energy cascade utilization system is constructed, and deep energy saving is achieved.

Description

Technical Field

[0001] This invention belongs to the field of integrated industrial salt production and nitrate production technology, specifically relating to a method for producing industrial salt based on multi-stage purification of high-nitrate brine. Background Technology

[0002] In the field of salt-nitrate separation production, conventional salt-nitrate separation evaporation systems are the core component of nitrate production. However, after completing the production of industrial salt, this system generates high-nitrate liquid, which contains high concentrations of sodium chloride and sodium sulfate, as well as a high content of impurities. Currently, the industry generally collects this high-nitrate liquid as waste and returns it to salt wells or treats it directly. This simple and extensive treatment method presents serious problems in terms of resource and energy utilization.

[0003] From a resource utilization perspective, both sodium chloride and sodium sulfate in high-nitrate liquor are important chemical raw materials. Sodium chloride is an indispensable raw material for producing basic chemical products such as chlorine and sodium hydroxide, while sodium sulfate has wide applications in industries such as glass, papermaking, and printing and dyeing. Directly discarding high-nitrate liquor is undoubtedly a huge waste of these valuable resources. In the current context of increasingly scarce resources and rising prices, this waste runs counter to the concept of sustainable development and significantly increases the production costs of enterprises.

[0004] From an energy utilization perspective, high-nitrate liquor, as a byproduct, still contains a certain amount of energy. Directly treating high-nitrate liquor cannot recover and utilize this energy, resulting in a huge energy loss. This not only increases the energy consumption costs of enterprises but also fails to meet the social development requirements of energy conservation and emission reduction.

[0005] Current technologies lack effective comprehensive utilization methods for high-nitrate solutions, failing to fully tap their potential value. The inadequate separation and recovery of sodium chloride and sodium sulfate in these solutions results in low resource utilization throughout the salt-nitrate separation process, hindering economic efficiency. Furthermore, the lack of integrated treatment technologies hinders the transformation of the salt-nitrate separation industry towards high efficiency, green practices, and sustainable development.

[0006] Furthermore, the handling of bromine is a challenging issue in the treatment of high-nitrate solutions and related production processes. The brine used in salt and nitrate production often contains bromide ions, which may be converted into elemental bromine during subsequent processing. However, residual trace amounts of free bromine in the liquid are volatile and corrosive. Without effective treatment, the liquid recycling process not only corrodes production equipment, shortens its lifespan, and increases maintenance and replacement costs, but also volatilizes into the air during production, polluting the environment and harming human health. Current technologies for bromine treatment are often inadequate, lacking efficient and environmentally friendly methods.

[0007] With increasingly stringent environmental protection requirements and intensifying resource constraints, the salt-nitrate separation industry faces enormous challenges. How to improve brine utilization, reduce brine discharge, and comprehensively utilize high-nitrate solutions while ensuring product quality and production efficiency, thereby maximizing resource utilization and achieving energy conservation and emission reduction in the production process, while effectively treating bromine and minimizing its harm to equipment and the environment, has become a pressing problem for the salt-nitrate separation industry.

[0008] Existing salt-nitrate separation processes and technologies cannot meet the needs of industry development, necessitating the development of a multi-stage purification and industrial salt production method based on high-nitrate brine. This process should effectively separate and recover sodium chloride and sodium sulfate from the high-nitrate solution, improving resource utilization. Simultaneously, it should fully utilize waste heat from the production process to reduce energy consumption and achieve energy conservation and emission reduction goals. Furthermore, it should ensure product quality and production efficiency, enhancing the company's economic benefits and market competitiveness. Summary of the Invention

[0009] The existing technology has the problem that the production of industrial salt using high-nitrate brine as raw material generates high-nitrate liquid, which is directly collected as waste and returned to the salt well or directly treated, resulting in serious resource waste and energy loss. To address the above problems, this invention provides a method for producing industrial salt based on multi-stage purification of high-nitrate brine, comprising the following steps: (1) The high-nitrate raw brine is successively processed through a primary reaction, carbonization reaction, plate membrane filtration, and preheating in a preheater before entering the salt production system to obtain refined salt, refined industrial salt and high-nitrate clear liquid; the primary reaction removes calcium ions, magnesium ions and iron ions from the high-nitrate raw brine; (2) The high-nitrate clear liquid is divided into three streams. The first stream, together with the high-nitrate original brine, enters the bromine removal system to remove Br2 and then enters the salt production system. The second stream enters the nitrification system to produce anhydrous sodium sulfate. The third stream enters the primary reaction tank to participate in the primary reaction.

[0010] Preferably, the heat of the salt tank in the salt production system is provided by boiler compressed steam (the boiler steam is processed by a steam turbine and a steam compressor in sequence to obtain boiler compressed steam).

[0011] Preferably, the heat of the nitrate-producing tank in the nitrate-producing system is provided by boiler back-pressure steam (boiler steam is processed by a steam turbine to generate back-pressure steam).

[0012] Preferably, the heat of the preheater 2 before nitrate precipitation in the nitrate production system is provided by boiler back pressure steam.

[0013] Preferably, the salt production system includes salt production tank 1, salt production tank 2, flash evaporation tank 1, salt production tank 3, flash evaporation tank 2, and salt production tank 4 connected in sequence. The salt production tanks of the salt production system obtain refined industrial salt of different grades through gradient cooling.

[0014] Preferably, the salt-making system includes four salt-making tanks connected in sequence: Salt-making Tank 1, Salt-making Tank 2, Flash Vaporization Tank 1, Salt-making Tank 3, Flash Vaporization Tank 2, and Salt-making Tank 4. The salt-making tanks of the system produce refined industrial salt of different grades through gradient cooling. The temperature ranges of Salt-making Tank 1, Salt-making Tank 2, Flash Vaporization Tank 1, Salt-making Tank 3, Flash Vaporization Tank 2, and Salt-making Tank 4 are 120±5℃, 120±5℃, 95±5℃, 88±5℃, 68±5℃, and 50±5℃, respectively.

[0015] Preferably, the bromine removal system removes Br2 by oxidative hot blowing. Bromine ions in the solution are oxidized to generate Br2. The blowing air for oxidative hot blowing is compressed air, and the heat in the oxidative hot blowing tank is provided by secondary steam generated in the flash tank II of the salt production system.

[0016] Preferably, compressed air in the bromine removal system is introduced into the bottom of the liquid in the oxidizing hot blowing tank, blowing the Br2 vapor and water vapor generated in the oxidizing hot blowing tank into the condensing device for condensation to form condensate. The liquid surface in the oxidizing hot blowing tank is connected to the condenser through a pipe. The condensate enters the separation device for static stratification (lower layer liquid bromine, upper layer water). The liquid bromine is pumped from the bottom of the separation device into the storage device. The liquid surface in the condensing device is connected to the tail gas treatment absorption device through a pipe. The gas above the liquid surface in the condensing device enters the chemical absorption liquid in the tail gas treatment absorption device through a pipe for chemical absorption, converting Br2 into bromine compounds.

[0017] Preferably, the bromine removal system is composed of a reaction tank, a clear liquid tank, an acid adjustment tank, an oxidizing hot blowing tank, and a regulating-reduction reaction tank connected in sequence; High-nitrate raw brine is pumped directly from the reaction tank into the debromination system; The regulating-reduction reaction vessel is connected to and communicates with the flash evaporation vessel 2 in the salt production system. The high-nitrate clear liquid enters the reaction vessel 1 in the bromine removal system from the salt production vessel 4 in the salt production system.

[0018] Preferably, the second high-nitrate clear liquid enters the nitrate-forming tank after being preheated by the second preheater. Nitrate is precipitated in the nitrate-forming tank. The nitrate slurry in the nitrate-forming tank is discharged from the salt leg into the nitrate thickener, centrifuge, and dried to obtain anhydrous sodium sulfate. The solution in the upper part of the nitrate-forming tank enters the second flash evaporation tank through the overflow port set at the upper part of the nitrate-forming tank.

[0019] Preferably, the boiler gas generated by the boiler undergoes denitrification (using a denitrification device), desulfurization and dust removal (using a desulfurization and dust removal device), and compression and condensation (compression-condensation device) before participating in the carbonization reaction.

[0020] The principle of a first-order reaction is as follows: CaO + H₂O → Ca(OH)₂; Ca(OH)2+Na2SO4→CaSO4↓+2NaOH; Mg2+ +2OH - →Mg(OH)2↓; Fe 3+ +3OH - →Fe(OH)3↓.

[0021] The principle of carbonization reaction is as follows: CO2↑ + 2NaOH → 2Na2CO3; Ca 2+ +CO3 2- →CaCO3↓.

[0022] The chemical reactions involved in the bromine removal system are as follows: (1) The reaction that occurs inside the reaction vessel: Mg 2+ +2OH - →Mg(OH)2↓; Fe 3+ +3OH - →Fe(OH)3↓; Ca 2+ +CO3 2- →CaCO3↓; (2) Reactions occurring inside the oxidizing hot blowing tank: ClO - +2Br - +2H + →Cl - +Br2+H2O; (3) Adjustment of the reaction occurring in the reduction reactor (to remove residual Br2 and NaClO): Sodium hydroxide and reducing agent Na2SO3 are added simultaneously to the adjustment-reduction reaction vessel to adjust the pH of the solution to 8.8-9.5.

[0023] The reactions occurring in the regulating-reduction reactor are as follows: Br2+Na2SO3+2NaOH→Na2SO4+2NaBr+2H2O; NaClO + Na₂SO₃ → Na₂SO₄ + NaCl.

[0024] Beneficial effects: (1) Traditional processes treat the high-nitrate liquid produced after industrial salt production as waste, resulting in a serious waste of valuable resources such as sodium chloride and sodium sulfate. This invention precisely diverts the high-nitrate clear liquid: one part is returned to the primary reaction for recycling, another part enters the nitrate production system to produce anhydrous sodium sulfate, and the remaining part is mixed with the high-nitrate raw brine and returned to the salt production system for further salt extraction. This design completely changes the fate of the high-nitrate liquid as waste, achieves efficient separation and recovery of sodium chloride and sodium sulfate, maximizes the utilization of valuable components in the brine, significantly reduces raw material consumption and production costs, and improves the overall economic benefits of the process. (2) This invention innovatively designs an energy circulation network based on boiler steam. The steam generated by the boiler first drives the turbine to do work, and the back pressure steam generated is used to heat the nitrate tanks; the steam from the turbine is then pressurized and heated by the compressor to form high-grade compressed steam, which in turn heats the first and second high-temperature salt tanks, and its condensation heat continues to heat the third and fourth salt tanks with lower temperatures. The waste steam after heating is finally used to provide a low-grade heat source for the oxidizing heat blowing tanks, tail gas absorption devices, etc. This heat is used multiple times according to the temperature gradient from high to low, forming an efficient and closed-loop thermal energy cascade utilization chain, which maximizes the recovery and utilization of system waste heat, significantly reduces the comprehensive energy consumption of industrial salt production, nitrate production and bromine removal, and meets the requirements of green development for energy conservation and emission reduction; (3) The bromine removal system specially designed in this invention involves several steps, including impurity removal, acid conditioning and oxidation hot blowing, blowing Br2 vapor and water vapor generated by the oxidation hot blowing tank into a condenser for condensation, and allowing the condensate to settle and separate in a separation device. Liquid bromine is then pumped from the bottom of the separation device into a storage device. The system also includes tail gas absorption and conversion, and finally, liquid re-conditioning and reduction reaction. These steps effectively convert bromine in the brine, existing in ionic form, into elemental bromine for recovery, solving the industry problem of residual free bromine corroding equipment and polluting the environment during the recycling process. Crucially, in the initial stage of the bromine removal system, the first high-nitrate clear liquid and the high-nitrate raw brine are mixed in a specific ratio in reaction tank one. This design produces multiple synergistic effects, as follows: a. Component optimization and reaction promotion: The introduction of high-nitrate raw brine effectively regulates the ionic composition and concentration of the mixed brine, creating a more favorable chemical environment for subsequent oxidation reactions. This promotes the more efficient and stable conversion of bromide ions into elemental bromine, thereby increasing the bromine blowing rate and recovery rate.

[0025] b. System material and heat balance: The influx of high-nitrate raw brine increases the total amount of material and heat capacity entering the salt production system, which helps stabilize the operating parameters (such as liquid level, concentration, and temperature) of the subsequent industrial salt evaporation system, reduces the system impact caused by fluctuations in the flow rate or composition of a single high-nitrate clear liquid, and enhances the robustness and continuous stable operation capability of the entire co-production process.

[0026] c. Resource integration and utilization: This hybrid approach essentially combines the pretreatment of high-nitrate raw brine with the debromination process, simplifying the process and realizing the synergistic treatment and resource integration of brine from different sources.

[0027] (4) This invention organically integrates multiple processes such as industrial salt production, nitrate production, bromine removal, primary reaction, and carbonization, forming a closely linked comprehensive production system. It not only achieves the co-production of main products (refined salt, refined industrial salt, and anhydrous sodium sulfate) and by-products (liquid bromine), but also reuses boiler flue gas for carbonization after denitrification, desulfurization, dust removal, compression, and condensation, realizing the recycling of carbon elements. The entire process has virtually no waste liquid discharge, minimizing environmental pollution. Simultaneously, product diversification enhances the ability to withstand market risks and improves overall profitability, achieving a harmonious balance between environmental protection and economic benefits. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the energy-saving and efficient integrated industrial salt production process for nitrate production according to Embodiment 1 of the present invention. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0030] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0031] It should be noted that, unless otherwise specified, the embodiments and features and technical solutions in the present invention can be combined with each other.

[0032] Example 1 As per the instruction manual Figure 1 The diagram shows a method for producing industrial salt based on multi-stage purification of high-nitrate brine provided by this invention. The process steps are as follows: (1) The high-nitrate raw brine is successively subjected to a first-stage reaction (the amount of quicklime added is 0.9-1.3 g / L), a carbonization reaction (the amount of CO2 aeration is increased, and the carbonization reaction ends when the CO2 aeration reaches the solution pH=9.8-10.3 and the aeration is stopped), filtration (plate membrane, pore size is 100-200 nm), and (preheater one) preheated to a temperature range of 120±5℃ before entering the salt making system to obtain refined industrial salt and high-nitrate clear liquid; after plate membrane filtration, refined brine is obtained; The principle of a first-order reaction is as follows: CaO + H₂O → Ca(OH)₂; Ca(OH)2+Na2SO4→CaSO4↓+2NaOH; Mg 2+ +2OH - →Mg(OH)2↓; Fe 3+ +3OH - →Fe(OH)3↓.

[0033] The principle of carbonization reaction is as follows: CO2↑ + 2NaOH → 2Na2CO3; Ca 2+ +CO3 2- →CaCO3↓.

[0034] The composition of high-nitrate raw brine is shown in Table 1: Table 1

[0035] The composition of the refined brine is shown in Table 2: Table 2

[0036] The composition of high-nitrate clear liquid is shown in Table 3: Table 3

[0037] The solution obtained from the adjustment-reduction tank has the following main components, as shown in Table 4: Table 4

[0038] The salt-making system consists of four salt-making tanks connected in sequence: Salt-making Tank 1, Salt-making Tank 2, Flash Vaporization Tank 1, Salt-making Tank 3, Flash Vaporization Tank 2, and Salt-making Tank 4. The salt-making tanks of the system produce salt of different grades through gradient cooling. The temperatures of Salt-making Tank 1, Salt-making Tank 2, Flash Vaporization Tank 1, Salt-making Tank 3, Flash Vaporization Tank 2, and Salt-making Tank 4 are 120±5℃, 120±5℃, 95±5℃, 88±5℃, 68±5℃, and 50±5℃, respectively. Salt-making Tank 1, Salt-making Tank 2, Flash Vaporization Tank 1, Salt-making Tank 3, Flash Vaporization Tank 2, and Salt-making Tank 4 are interconnected via overflow. The liquid level in the salt-making tanks and flash evaporation tanks is controlled to not exceed the liquid level line corresponding to 85% of the tank volume and not fall below the liquid level line corresponding to 50% of the tank volume.

[0039] In the salt-making system, the heat for the salt-making tanks is provided by compressed steam from the boiler (the boiler steam is processed sequentially by a steam turbine and a steam compressor to obtain compressed steam). The compressed steam heats the brine in the heating chamber of the salt-making tank. Simultaneously, the compressed steam enters the heating chambers of salt-making tank one, salt-making tank two, and salt-making tank three to directly heat the salt-making tanks. Meanwhile, the secondary steam generated in the heating chambers of salt-making tanks one and two flows back to the steam compressor from the top of the salt-making tanks. The secondary steam from flash evaporation tank one enters the heating chamber of salt-making tank three from the top of flash evaporation tank one. The secondary steam generated in the heating chamber of salt-making tank three enters the heating chamber of flash evaporation tank two from the top of flash evaporation tank two. The secondary steam generated in the heating chamber of flash evaporation tank two enters the heating chamber of salt-making tank four from the top of flash evaporation tank two.

[0040] The high-nitrate clear liquid produced in step (1) is divided into three streams. The first stream (accounting for 15-20% of the high-nitrate clear liquid) along with the high-nitrate raw brine after filtration (plate membrane, pore size is 100-200nm) enters the bromine removal system to remove Br2 and then enters the salt production system. The second stream (accounting for 65-75% of the total volume of the high-nitrate clear liquid) enters the nitrification system to produce anhydrous sodium sulfate. The third stream (the remaining high-nitrate clear liquid) enters the primary reaction tank to participate in the primary reaction.

[0041] The first stream of high-nitrate clarified solution enters reaction tank one, while the high-nitrate raw brine is also pumped into reaction tank one. They mix within reaction tank one of the bromine removal systems (which removes calcium, magnesium, and iron ions from the high-nitrate raw brine and reduces the carbonate and hydroxide content in the high-nitrate clarified solution). The solution in reaction tank one then... 2+ ≤10.0mg / L, Mg 2+ Once the concentration reaches ≤5.0 mg / L, stop pumping high-nitrate raw brine into reaction tank one. Then, pump the solution from reaction tank one into a clear liquid tank (the clear liquid tank is a storage tank for storing clear liquid). Next, pump it into an acid-adjusting tank to adjust the pH to 3-5. After that, pump it into an oxidizing hot blowing tank. The solution in the oxidizing hot blowing tank flows out from the bottom and enters the adjustment-reduction reaction tank to undergo a reduction reaction (the alkali adjustment tank adjusts the pH to 8.8-9.5, the alkali is caustic soda, and the reducing agent is sodium sulfite, which reduces residual elemental bromine and sodium hypochlorite to bromide ions and chloride ions, respectively). Elemental bromine is reduced to bromide ions. Then, pump the liquid in the adjustment-reduction tank into flash tank two of the industrial salt production system.

[0042] (2) The bromine removal system consists of a reaction tank, a clear liquid tank, an acid adjustment tank, an oxidative hot blowing tank, and a regulating-reduction reaction tank connected in sequence. The bromine removal system also includes a condensation device, a separation device, and a storage device connected in sequence to the oxidative hot blowing tank. Bromine ions in the solution of the oxidative hot blowing tank are oxidized by compressed air to generate Br2, and the Br2 vapor generated above the liquid surface of the oxidative hot blowing tank is blown into the condensation device (temperature 0-5℃) by compressed air hot blowing (Br2 vapor is blown in from the bottom of the absorption device). The liquid bromine is obtained by the liquid bromine and water separation device and enters the liquid bromine storage device.

[0043] The heat inside the oxidizing hot blowing tank (65-75℃) is provided by the secondary steam from the flash evaporation tank 2. The heating method of the secondary steam from the flash evaporation tank 2 to the oxidizing hot blowing tank is the same as the heating method of the boiler compressed steam to the salt production tank. Both are preheated through the heating chamber, but no heat is recovered.

[0044] The second high-nitrate clear liquid enters the nitrate production system. After being preheated to 110±5℃ by (preheater two), it enters the nitrate production tank (temperature is 110±5℃). Nitrate is precipitated in the nitrate production tank. The solid crystals precipitated in the nitrate production tank are collected and dried to obtain anhydrous sodium sulfate.

[0045] In the nitrate production system, the heat for the nitrate-producing tank is provided by boiler back-pressure steam (boiler steam is processed by a steam turbine to generate back-pressure steam). The method of heating the nitrate-producing tank with boiler back-pressure steam is the same as the method of heating the salt-producing tank with boiler compressed steam, both of which are heated through an insulated jacket, but without heat recovery.

[0046] In the nitrate production system, the heat of the preheater (preheater 2) before nitrate precipitation is provided by an electric heating jacket or back pressure steam.

[0047] The boiler steam generated by the boiler passes through denitrification (using a denitrification device), desulfurization and dust removal (using a desulfurization and dust removal device), and compression and condensation (compression-condensation device) in sequence before participating in the first-stage reaction. The boiler gas composition after desulfurization and dust removal is: N2, O2, CO2, moisture, trace SO2, and the temperature is 35~50℃.

[0048] The present invention uses the above-described process to produce industrial salt and nitrates. The quality (composition) of the refined industrial salt separated from the four salt legs of the salt-making tank is shown in Table 5. Table 5

[0049] The quality (composition) of anhydrous sodium sulfate obtained after solid-liquid separation and drying of the solution in the nitrate preparation tank is shown in Table 6: Table 6

[0050] For those skilled in the art, the specific meanings of the above terms in this invention can be understood according to the specific circumstances. Obviously, the embodiments described above are merely some embodiments of this invention, not all embodiments. The accompanying drawings show preferred embodiments of the invention, but do not limit the patent scope of this invention. This invention can be implemented in many different forms; rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this invention. Although the invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this specification and drawings, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this invention.

Claims

1. A method for producing industrial salt based on multi-stage purification of high-nitrate brine, characterized in that, Includes the following steps: (1) The high-nitrate raw brine is successively processed through a primary reaction, carbonization reaction, plate membrane filtration, and preheating in a preheater before entering the salt production system to obtain refined salt, refined industrial salt and high-nitrate clear liquid; the primary reaction removes calcium ions, magnesium ions and iron ions from the high-nitrate raw brine; (2) The high-nitrate clear liquid is divided into three streams. The first stream, together with the high-nitrate original brine, enters the bromine removal system to remove Br2 and then enters the salt production system. The second stream enters the nitrification system to produce anhydrous sodium sulfate. The third stream enters the primary reaction tank to participate in the primary reaction.

2. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The heat for the salt-making tanks in the salt-making system is provided by compressed steam from the boiler.

3. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The heat of the nitrate-producing tank in the nitrate-producing system is provided by the back pressure steam of the boiler.

4. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 3, characterized in that, The heat of the preheater 2 before nitrate precipitation in the nitrate production system is provided by the boiler back pressure steam.

5. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The bromine removal system removes Br2 by oxidative hot blowing. Bromine ions in the solution in the oxidative hot blowing tank are oxidized by air to generate Br2. The oxidative hot blowing gas is compressed air, and the heat in the oxidative hot blowing tank is provided by the secondary steam generated in the flash tank 2 of the salt production system.

6. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 5, characterized in that, Compressed air in the bromine removal system is introduced into the bottom of the liquid in the oxidizing hot blowing tank, blowing the Br2 vapor and water vapor generated in the oxidizing hot blowing tank into the condensing device for condensation to form condensate. The liquid surface in the oxidizing hot blowing tank is connected to the condenser through a pipe. The condensate enters the separation device for static stratification. Liquid bromine is pumped from the bottom of the separation device into the storage device. The liquid surface in the condensing device is connected to the tail gas treatment absorption device through a pipe. The gas above the liquid surface in the condensing device enters the chemical absorption liquid in the tail gas treatment absorption device through a pipe for chemical absorption, converting Br2 into bromine compounds.

7. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The salt production system includes salt production tank 1, salt production tank 2, flash evaporation tank 1, salt production tank 3, flash evaporation tank 2, and salt production tank 4 connected in sequence. The salt production tanks of the salt production system obtain salt products of different grades through gradient cooling.

8. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The bromine removal system consists of a reaction tank, a clear liquid tank, an acid adjustment tank, an oxidizing hot blowing tank, and a regulating-reduction reaction tank connected in sequence. High-nitrate raw brine is pumped into the bromine removal system from the reaction tank. The regulating-reduction reaction tank is connected to the flash evaporation tank 2 in the salt production system. High-nitrate clear liquid enters the reaction tank 1 in the bromine removal system from the salt production tank 4 in the salt production system.

9. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The second high-nitrate clear liquid enters the nitrate-forming tank after being preheated by the second preheater. Nitrate is precipitated in the nitrate-forming tank. The nitrate slurry in the nitrate-forming tank is discharged from the salt leg into the nitrate thickener, centrifuge, and dried to obtain anhydrous sodium sulfate. The solution in the upper part of the nitrate-forming tank enters the second flash evaporation tank through the overflow port set at the top of the nitrate-forming tank.

10. The method for producing industrial salt based on multi-stage purification of high-nitrate brine according to claim 1, characterized in that, The boiler gas produced by the boiler undergoes denitrification, desulfurization and dust removal, compression and condensation before participating in the carbonization reaction.

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