Efficient cooling process based on potassium nitrate production

Abstract

The application discloses a kind of high-efficiency cooling process based on potassium nitrate production in chemical process technical field, including dissolving dispersion, circulating cooling, seed-induced crystallization and vacuum-assisted cooling step.Potassium nitrate crude product is dissolved in deionized water and heated stirring, shear dispersion is added to barium calcium zirconate titanate and lithium silicate composite nano cooling accelerator, and dispersion solution is obtained;Dispersed solution is pumped into heat exchanger and cooled, and then returned to crystallization kettle;When the temperature drops to the appropriate range, potassium nitrate seed is added to induce crystallization;Start vacuum cooling system to assist cooling to room temperature, centrifugal separation after crystallization aging, solid is washed with ice water and dried to obtain product.Composite nano cooling accelerator is prepared by solvothermal method to prepare barium calcium zirconate titanate nano core, modified by anhydrous silane coupling agent grafting, then coated with lithium silicate mesoporous shell, and finally modified with surface hydrophilicity.The application improves the crystallization efficiency and product particle size uniformity, and the mother liquor can be recycled, to reduce energy consumption and production cost.

Description

Technical Field

[0001] This invention relates to the field of chemical process technology, specifically to a high-efficiency cooling process for potassium nitrate production. Background Technology

[0002] Potassium nitrate, as an important inorganic chemical raw material, is widely used in agricultural fertilizers, food additives, pharmaceutical manufacturing, and pyrotechnic products. With the continuous expansion of industrial production scale and increasingly stringent product quality requirements, optimizing the potassium nitrate production process has become a key focus of the industry. Traditional potassium nitrate production processes mainly employ metathesis or ion exchange methods, with cooling crystallization being a crucial step determining product purity, crystal morphology, and particle size. In existing industrial production, potassium nitrate solutions are typically cooled and crystallized through natural cooling or mechanical refrigeration. This process suffers from low cooling efficiency, high energy consumption, and uneven crystal particle size distribution. Especially in large-scale continuous production, uneven temperature distribution within the crystallization vessel can easily lead to excessively high local supersaturation, triggering the formation of numerous fine crystals and affecting the product's filtration performance and drying efficiency. Furthermore, crystal adhesion and scaling on heat exchanger surfaces are also common, not only reducing heat transfer efficiency but also increasing the frequency and cost of equipment cleaning and maintenance, thus hindering further improvements in production efficiency and economic benefits.

[0003] To improve the heat transfer efficiency and crystal quality of potassium nitrate during cooling crystallization, various enhancement measures have been attempted in existing technologies, including optimizing heat exchanger structure, improving stirring methods, and adding seed crystals to induce crystallization. However, these methods mostly focus on equipment-level improvements or process parameter adjustments, paying insufficient attention to the microscopic heat transfer mechanism and crystal growth kinetics control during crystallization. Some studies have attempted to add inorganic salts or organic polymer additives to the crystallization system to change the physical properties of the solution, but these additives often suffer from poor dispersion stability, easy introduction of impurity ions, and difficulty in separating them from the product, affecting the final purity and application performance of potassium nitrate. In recent years, nanomaterials have shown promising applications in the field of heat transfer enhancement. Nanofluids can effectively improve the thermal conductivity and convective heat transfer coefficient of solutions, but their application in potassium nitrate crystallization processes is relatively limited. Existing nano-additives are mostly single-component metal oxides or carbon-based materials with relatively limited functions, making it difficult to simultaneously meet the multiple requirements of dispersion stability, heat transfer promotion, and crystal morphology control. Furthermore, there is a lack of dedicated nano-promoter design and preparation technologies for potassium nitrate crystallization systems.

[0004] Furthermore, the application of nanoparticles in crystallization systems faces challenges related to surface modification and compatibility. Unmodified nanoparticles are prone to agglomeration and sedimentation in solution, failing to fully utilize their heat transfer enhancement effect and potentially becoming heterogeneous nucleation centers, leading to increased crystal defects. Although existing studies have used silane coupling agents to modify the surface of nanoparticles to improve their dispersibility in organic or inorganic systems, the surface functionalization design of nano-accelerators for potassium nitrate aqueous solution crystallization systems is still imperfect, especially with few reports on composite nanostructures possessing both hydrophilicity and crystallization induction functions. Simultaneously, the complexity and cost of nano-accelerator preparation processes are also significant factors restricting their industrial application. Existing nanomaterial synthesis methods often require high-temperature, high-pressure conditions or expensive raw materials, making it difficult to meet the economic requirements of large-scale potassium nitrate production. Therefore, developing a highly efficient composite nano-cooling accelerator specifically designed for potassium nitrate cooling crystallization processes, and establishing corresponding preparation methods and application processes, has significant theoretical and practical value for improving potassium nitrate production efficiency, reducing energy consumption, and improving product quality. This is the core technical problem that this invention aims to solve. Summary of the Invention

[0005] The purpose of this invention is to provide a high-efficiency cooling process for potassium nitrate production, which solves the technical problems of low cooling crystallization efficiency, high energy consumption, uneven crystal particle size distribution, and easy scaling of heat exchangers in existing potassium nitrate cooling processes.

[0006] The present invention achieves the above objectives through the following technical solutions: A high-efficiency cooling process for potassium nitrate production includes the following steps: S1, by weight, add 90-110 parts of crude potassium nitrate to 110-130 parts of deionized water, heat to 75-85℃, stir, add 0.05-0.15 parts of barium calcium zirconate titanate-lithium silicate composite nano cooling promoter, shear and disperse to obtain a dispersed solution. S2, the dispersed solution is pumped into a heat exchanger for cooling, and then returned to the crystallization vessel; S3, when the temperature of the dispersed solution in the crystallization vessel drops to 45-50℃, add 0.5-1.0 parts of potassium nitrate seed crystals to the crystallization vessel and cool; S4. Start the vacuum cooling system to assist in cooling down until the temperature drops to 20-25℃, crystallization and aging occur. After crystallization is complete, discharge the crystal slurry, centrifuge to separate it, and obtain the solid. Wash the solid with ice water at 4-6℃ and dry it in a fluidized bed dryer at 80-90℃.

[0007] In this invention, the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter functions through multiple mechanisms in the potassium nitrate cooling crystallization process. The barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter forms a stable dispersion system in the solution, increasing the effective thermal conductivity of the solution and enhancing convective heat transfer between the heat exchanger and the solution. The perovskite core in the core-shell structure has a high phonon mean free path, enabling rapid heat transfer, while the mesoporous lithium silicate shell provides a large specific surface area, enhancing the heat exchange efficiency between the particles and the solution. The surface functional groups have a certain compatibility with potassium nitrate crystals, preventing the nanoparticles from becoming heterogeneous nucleation centers, and simultaneously regulating the diffusion rate of solute molecules during crystal growth, promoting uniform crystal growth. The segmented cooling process and the nano-promoter work synergistically, ensuring sufficient dispersion of nanoparticles during the high-temperature dissolution stage, precise control of supersaturation during the medium-temperature seed crystal addition stage, and further enhancing the heat transfer process through vacuum-assisted cooling during the low-temperature crystallization stage, ultimately yielding a potassium nitrate crystal product with uniform particle size and high purity.

[0008] According to a preferred embodiment of the present invention, in step S1, the shearing and dispersion time is 10-20 min.

[0009] According to a preferred embodiment of the present invention, in step S2, the temperature is cooled to 45-55°C.

[0010] According to a preferred embodiment of the present invention, in step S3, the temperature is cooled to 32-38°C.

[0011] According to a preferred embodiment of the present invention, in step S4, the crystallization aging time is 1.0-2.0 h.

[0012] According to a preferred embodiment of the present invention, the preparation steps of the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator include: A1, by weight, 5.8-6.2 parts of zirconium tetrachloride and 8.2-8.6 parts of tetrabutyl titanate are mixed. First, 8.0-8.5 parts of barium nitrate and 3.0-3.5 parts of calcium nitrate are dissolved in a mixed solvent of 75-85 parts of anhydrous ethanol and 18-22 parts of ethylene glycol methyl ether to obtain solution A. Zirconium tetrachloride and tetrabutyl titanate are added to solution A and stirred at room temperature to obtain a precursor solution. The precursor solution is transferred to a reaction vessel, sealed, and placed in a constant temperature drying oven. The temperature is raised to 195-205℃ for a solvothermal reaction. After the reaction is completed, it is naturally cooled to room temperature to obtain a precipitate. The precipitate is washed with anhydrous ethanol and deionized water and vacuum dried to obtain a dried solid. The dried solid is transferred to a muffle furnace and calcined at 495-505℃, then calcined at 845-855℃, and cooled to room temperature with the furnace to obtain barium calcium zirconate titanate nanocore particles. A2. Barium calcium zirconate titanate nanoparticles were ultrasonically dispersed in 145-155 parts of anhydrous toluene to obtain a suspension. Then, 4.3-4.7 parts of 3-aminopropyltriethoxysilane were added to the suspension sequentially. Under nitrogen protection, the reaction was carried out at 78-82℃. After cooling, 3.0-3.4 parts of γ-glycidoxypropyltrimethoxysilane were added, and the temperature was further increased to 108-112℃ for reflux reaction. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed with toluene, anhydrous ethanol, and deionized water to obtain the washed solid. The washed solid was dried in a vacuum drying oven at 58-62℃ to obtain modified nanoparticles with amino and epoxy bifunctional groups grafted on the surface. A3, at room temperature, ultrasonically disperse 2.8-3.2 parts of modified nanoparticles with amino and epoxy bifunctional groups grafted onto their surface in a mixed solvent of 95-105 parts anhydrous ethanol and 50-55 parts deionized water. After ultrasonic treatment, add 1.6-2.0 parts of hexadecyltrimethylammonium bromide, continue stirring, and dropwise add 6.0-7.0 parts of tetraethyl orthosilicate. Simultaneously, dropwise add 2.6-3.0 parts of lithium metasilicate tetrahydrate dissolved in 15-25 parts of deionized water. After the addition is complete... Afterwards, the pH was adjusted to 9.5-10.0, and the reaction was continued to be stirred in a water bath at 38-42℃ to obtain a reaction mixture. The reaction mixture was transferred to a reaction vessel and subjected to hydrothermal treatment at 98-102℃. After cooling, the mixture was centrifuged to collect the solid product. The solid product was washed with anhydrous ethanol and deionized water to obtain the washed solid product. The washed solid product was placed in a muffle furnace and calcined at 520-540℃ to obtain composite nanoparticles coated with lithium silicate shell. A4. The composite nanoparticles coated with lithium silicate shells are immersed in a solution of 0.4-0.6 parts γ-aminopropyltriethoxysilane, 0.2-0.4 parts glacial acetic acid, and 18-22 parts anhydrous ethanol. The mixture is stirred and reacted at 48-52℃, centrifuged, and the solid product is collected. The solid product is washed with anhydrous ethanol to obtain the washed solid. The washed solid is dried in a vacuum drying oven at 48-52℃ and then heat-treated in a vacuum drying oven at 78-82℃.

[0013] In this invention, the preparation of the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter is based on a multi-step chemical reaction and structural assembly process. Its core formation mechanism involves the synergistic effect of metal alkoxide hydrolysis and condensation followed by solvothermal crystallization. In the core particle synthesis stage, zirconium tetrachloride and tetrabutyl titanate serve as zirconium and titanium sources, respectively, undergoing hydrolysis in a mixed alcohol solvent system to generate corresponding metal hydroxide intermediates. Barium nitrate and calcium nitrate, after dissolution, provide barium and calcium ions, which co-precipitate with the zirconium titanate hydroxide under solvothermal conditions. As the reaction temperature increases, the metal ions in the precursor solution gradually align, forming crystal nuclei with a perovskite-type crystal structure. In a constant-temperature, closed environment, the high temperature and high pressure conditions of the solvent promote crystal growth and increase crystallinity, gradually transforming the amorphous precipitate into barium calcium zirconate titanate nanoparticles with a regular crystal structure. The subsequent staged calcination process is crucial. The low-temperature calcination stage primarily removes organic residues and water of crystallization, allowing for the initial formation of the particle framework. The high-temperature calcination stage further refines the crystal structure, controls grain size, and eliminates lattice defects, resulting in nanocores with high thermal conductivity and chemical stability. This perovskite-structured metal oxide possesses excellent heat transfer capabilities, effectively enhancing heat transfer processes in solution. In the core particle surface modification stage, a two-step silane coupling agent grafting reaction is employed to introduce bifunctional groups. In the first step, an amino-containing silane coupling agent undergoes a condensation reaction with hydroxyl groups on the nanoparticle surface in anhydrous toluene solvent. After hydrolysis, the siloxane groups form stable siloxane bonds with the particle surface, while the amino groups face outwards. In the second step, an epoxy-containing silane coupling agent continues to react with the remaining surface hydroxyl groups, forming a bifunctionalized surface with coexisting amino and epoxy groups. This bifunctional group design provides active sites for subsequent shell growth. The amino groups are nucleophilic, and the epoxy groups are reactive; their synergistic effect enhances the adsorption and reaction of the shell precursor on the core surface. The formation of the lithium silicate shell is based on the principles of sol-gel chemistry. Tetraethyl orthosilicate and lithium metasilicate serve as silicon and lithium sources, respectively, undergoing a hydrolysis-condensation reaction under alkaline conditions. Tetraethyl orthosilicate hydrolyzes to generate silanol groups, which condense to form a silicon-oxygen-silicon network structure. Simultaneously, lithium ions from lithium metasilicate embed into this network, forming a mesoporous lithium silicate shell. Hydrothermal treatment promotes the densification and crystallization of the shell, resulting in a strong chemical bond between the shell and the core. The final surface hydrophilic modification is achieved through the reaction of aminopropylsilane with the remaining hydroxyl groups on the shell surface. The introduced amino groups enhance the dispersion stability of the nanoparticles in aqueous solution, enabling them to remain suspended in potassium nitrate mother liquor for extended periods without agglomeration or sedimentation.

[0014] According to a preferred embodiment of the present invention, in step A1, the calcination time at 845-855°C is 6-8 hours.

[0015] According to a preferred embodiment of the present invention, in step A2, the reflux reaction time at 108-112°C is 6-8 hours.

[0016] According to a preferred embodiment of the present invention, in step A3, the hydrothermal treatment at 98-102°C is carried out for 24-30 hours.

[0017] According to a preferred embodiment of the present invention, in step A4, the stirring reaction time at 48-52°C is 6-8 hours.

[0018] The beneficial effects of this invention are as follows: This invention provides a highly efficient cooling process for potassium nitrate production. By introducing a composite nano-cooling accelerator of barium calcium zirconate titanate and lithium silicate, it significantly improves the heat transfer efficiency and crystal quality during the crystallization process. The composite nano-accelerator forms a stable nanofluid system in the potassium nitrate aqueous solution, effectively improving the thermal conductivity and convective heat transfer coefficient of the solution, making heat transfer more uniform and rapid during the cooling process. Compared with traditional cooling processes, this invention can shorten the cooling time, reduce refrigeration energy consumption, and reduce crystal adhesion and scaling on the heat exchanger surface, extending the equipment cleaning cycle and reducing maintenance costs. By combining segmented temperature-controlled cooling with seed-induced crystallization, the supersaturation during the crystallization process is effectively controlled, avoiding the formation of a large number of fine crystals, resulting in a more uniform crystal particle size distribution in the product. Filtration performance and drying efficiency are significantly improved, and the purity and appearance quality of the final product meet or exceed industry standards.

[0019] The composite nano-cooling accelerator used in this invention features a unique core-shell structure. The barium calcium zirconate titanate nanocore, acting as a heat transfer enhancement component, possesses excellent thermal properties and chemical stability, maintaining a dispersed state within the crystallization temperature range without agglomeration or sedimentation. The lithium silicate mesoporous shell not only provides excellent hydrophilicity, enabling long-term stable dispersion of nanoparticles in aqueous solution, but also enhances the compatibility between the nanoparticles and the potassium nitrate crystal surface through modification with amino and epoxy bifunctional groups, preventing nanoparticles from becoming heterogeneous nucleation centers and thus increasing crystal defects. After surface hydrophilic modification, the composite nano-accelerator exhibits excellent dispersion stability in potassium nitrate mother liquor, allowing for recycling with the mother liquor without additional separation. This reduces production costs and avoids the impact of nanomaterial residues on product purity, achieving efficient utilization of nano-additives and green production.

[0020] From an industrial application perspective, the cooling process of this invention has advantages such as simple operation, strong adaptability, and significant economic benefits. The entire process does not require large-scale modifications to existing production equipment; technological upgrades can be achieved simply by adding a nano-accelerator and optimizing cooling parameters during the dissolution process. The preparation process of the composite nano-accelerator is mature and controllable, with widely available raw materials and reasonable production costs, making it suitable for large-scale industrial production. Through the synergistic effect of vacuum cooling and mechanical refrigeration, energy consumption is further reduced, cooling efficiency is improved, and the overall energy consumption per unit product is significantly reduced. Furthermore, the potassium nitrate product produced by this invention has regular crystal morphology, uniform particle size, and good flowability, facilitating subsequent packaging, storage, and transportation. It exhibits superior performance in applications such as agricultural fertilizers, food processing, and pharmaceutical manufacturing, with broad market prospects and significant promotional application value and economic and social benefits. Detailed Implementation

[0021] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content. Example 1

[0022] This embodiment provides a high-efficiency cooling process for potassium nitrate production, including the following steps: S1. 100g of industrial-grade crude potassium nitrate (92.5% potassium nitrate content) is added to 120g of deionized water and heated to 80℃ in a dissolving tank. The mixture is stirred at 250rpm for 30min to form a saturated potassium nitrate solution. Then, based on the mass of the industrial-grade crude potassium nitrate, 0.10g of barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is added. The mixture is dispersed in a high-shear emulsifier at 6000rpm for 10min to ensure that the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is uniformly dispersed in the potassium nitrate solution, forming a stable solid-liquid suspension system. The dispersed solution is filtered through a 100-mesh sieve to remove undissolved particles and then transferred to the pre-cooling crystallization system storage tank for later use. S2, the potassium nitrate solution containing barium calcium zirconate titanate-lithium silicate composite nano cooling promoter obtained in step S1 is pumped into the external circulation cooling loop at a flow rate of 90 m³ / h. The core equipment of this cooling loop is a detachable spiral plate heat exchanger with a heat exchange area of ​​50 m². The cooling medium of the heat exchanger is chilled water with a circulation rate of 10°C. The potassium nitrate solution passes through the spiral plate heat exchanger at a flow rate of 1.5 m / s. Under the action of the barium calcium zirconate titanate-lithium silicate composite nano cooling promoter, the solution forms micro-scale turbulent disturbances near the heat exchange surface, which enhances heat transfer while preventing the nucleation and adhesion of crystals on the heat exchange plate surface. After being cooled by the heat exchanger, the solution temperature drops to 50°C and is then returned to the crystallization vessel. This circulation process is carried out continuously, keeping the solution temperature in the crystallization vessel decreasing uniformly at a rate of 4°C / h. S3. When the solution temperature in the crystallization vessel drops to 48℃, the solution state is monitored in real time using an online turbidity meter and a supersaturation detector. When the supersaturation of the solution reaches 1.04, 0.8g of potassium nitrate seed crystals with an average particle size of 90 mesh are added to the crystallization vessel. At the same time as adding the seed crystals, the stirring speed of the crystallization vessel is adjusted to a low-speed stirring mode of 100rpm, and the flow rate of the chilled water in the cooling circulation loop is adjusted simultaneously to control the solution cooling rate at 2.5℃ / h, maintaining the supersaturation of the solution within the metastable range of 1.02. This cooling process lasts for 3.0h, and the solution temperature gradually drops to 35℃. During this process, the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter significantly inhibits the adhesion and growth of crystals on the heat exchanger surface through the synergistic effect of microscale turbulence disturbance generated by its core-shell structure and surface hydrophilicity, while promoting the uniformity of crystal particle size distribution. S4. After step S3 is completed, the vacuum cooling system is activated to assist in cooling, controlling the vacuum degree inside the crystallization vessel to 1.2 kPa, so that the solution is further flash-cooled under vacuum conditions. The cooling rate is controlled at 1.5℃ / h until the solution temperature drops to 22℃. This temperature is maintained for 1.0h of continued crystallization and aging to allow potassium nitrate crystals to grow fully. The total time for the entire cooling and crystallization process is 10h. After crystallization, the crystal slurry is discharged and solid-liquid separation is performed by a centrifuge at a speed of 1350 rpm for 15 min. The separated solid is washed twice with 250g of 5℃ ice water and then dried in a fluidized bed dryer at 85℃ until the moisture content is less than 0.2%, thus obtaining industrial-grade potassium nitrate product. Part of the separated mother liquor is recycled for the dissolution process in step one. The barium calcium zirconate titanate-lithium silicate composite nano cooling promoter remains in a stable dispersion state during the mother liquor circulation process and can be reused for 4 batches before appropriate replenishment.

[0023] The preparation steps of the barium titanate-calcium silicate composite nano-cooling accelerator include: A1. Mix 6.0g zirconium tetrachloride, 8.4g tetrabutyl titanate, 8.2g barium nitrate, and 3.2g calcium nitrate. Dissolve the above raw materials in a mixed solvent of 80g anhydrous ethanol and 20g ethylene glycol methyl ether. The operation is carried out in a closed fume hood, with operators wearing gas masks and protective gloves. Stir at 300rpm for 30min at room temperature to form a homogeneous precursor solution. Then, transfer the precursor solution to a 200mL stainless steel autoclave lined with polytetrafluoroethylene, seal it, and place it in a constant temperature drying oven. Heat to 200℃ at a heating rate of 5℃ / min and maintain the temperature for 24 hours. h was subjected to solvothermal treatment, and after the reaction was completed, it was naturally cooled to room temperature. The precipitate was washed three times by alternating centrifugation with anhydrous ethanol and deionized water. Each centrifugation speed was 8000 rpm and the time was 15 min. The washed precipitate was collected and placed in a vacuum drying oven and dried at 80℃ for 12 h. The dried solid powder was transferred to a programmable muffle furnace and heated from room temperature to 500℃ at a heating rate of 2℃ / min and held at that temperature for 3 h. Then, the temperature was further increased to 850℃ at a heating rate of 2℃ / min and calcined for 6 h. Finally, it was naturally cooled to room temperature with the furnace to obtain barium calcium zirconate titanate nanocore particles with perovskite structure. In step A2, 5.0 g of barium calcium zirconate titanate nanoparticles prepared in step A1 were ultrasonically dispersed in 150 g of anhydrous toluene at a power of 200 W for 30 min to form a uniform suspension. Then, 4.5 g of 3-aminopropyltriethoxysilane was added to the suspension to initiate the first stage of the reaction. The reaction was carried out at 80 °C for 6 h under nitrogen protection. After cooling, 3.2 g of γ-glycidyl etheroxypropyltrimethoxysilane was added, and the reaction was continued at 110 °C under reflux for 6 h. During the reaction, the magnetic stirring speed was maintained at 400 rpm. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was collected by centrifugation at 10000 rpm for 20 min. The solid product was washed three times each with toluene, anhydrous ethanol, and deionized water to remove unreacted silane coupling agent. The washed solid was dried in a vacuum drying oven at 60 °C for 24 h to obtain modified nanoparticles with amino and epoxy bifunctional groups grafted on the surface. A3, at room temperature, 3.0 g of the surface-functionalized modified nanoparticles prepared in step A2 were ultrasonically dispersed in a mixed solvent of 100 g anhydrous ethanol and 52 g deionized water. After ultrasonic treatment for 20 min, 1.8 g of cetyltrimethylammonium bromide (CTAB) with a purity of 99.0% was added as a template agent, and stirring was continued for 30 min until completely dissolved. Subsequently, 6.5 g of tetraethyl orthosilicate was slowly added dropwise as the main silicon source under vigorous stirring, while 2.8 g of lithium metasilicate tetrahydrate dissolved in 20 g of deionized water was added dropwise as a lithium source solution, with the dropping rate controlled at 0.5 mL / m. After the addition of ammonia, the pH of the system was adjusted to 9.8. The reaction was continued for 6 hours in a 40°C water bath to carry out the sol-gel reaction. After the reaction was completed, the reaction system was transferred to a polytetrafluoroethylene-lined reactor and subjected to hydrothermal treatment at 100°C for 24 hours to promote the condensation and densification of the lithium silicate network. After cooling, the solid product was collected by centrifugation and washed three times each with anhydrous ethanol and deionized water. Then, the solid product was placed in a muffle furnace and calcined at 530°C for 5 hours to remove the CTAB template agent, thus obtaining composite nanoparticles with a mesoporous lithium silicate shell coating. A4. The composite nanoparticles with mesoporous lithium silicate shells prepared in step A3 were immersed in a surface hydrophilic modification solution prepared by 0.5 g γ-aminopropyltriethoxysilane, 0.3 g glacial acetic acid as a hydrolysis catalyst, and 20 g anhydrous ethanol. The solution was stirred at 50 °C for 6 h to carry out a sol-gel reaction. After centrifugation, the solid was washed three times with anhydrous ethanol. The washed solid was dried in a vacuum drying oven at 50 °C for 12 h, and then heat-treated in a vacuum drying oven at 80 °C for 4 h to finally obtain a core-shell-dendritic structure barium titanate-lithium silicate composite nano-cooling promoter. Example 2

[0024] This embodiment provides a high-efficiency cooling process for potassium nitrate production, including the following steps: S1. Add 95g of industrial-grade crude potassium nitrate (93.0% potassium nitrate content) to 115g of deionized water. Heat the solution to 78°C in a dissolving tank and maintain the stirring speed at 220rpm for 30min to form a saturated potassium nitrate solution. Then, add 0.12g of barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator based on the mass of the industrial-grade crude potassium nitrate. Disperse the solution using a high-shear emulsifier at 6000rpm for 12min to ensure that the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is uniformly dispersed in the potassium nitrate solution, forming a stable solid-liquid suspension system. After dispersing, filter the solution through a 100-mesh sieve to remove undissolved particles and transfer it to the pre-cooling crystallization system storage tank for later use. S2, the potassium nitrate solution containing barium calcium zirconate titanate-lithium silicate composite nano cooling promoter obtained in step S1 is pumped into the external circulation cooling loop at a flow rate of 80 m³ / h. The core equipment of this cooling loop is a detachable spiral plate heat exchanger with a heat exchange area of ​​45 m². The cooling medium of the heat exchanger is chilled water with a circulation rate of 8°C. The potassium nitrate solution passes through the spiral plate heat exchanger at a flow rate of 1.3 m / s. Under the action of the barium calcium zirconate titanate-lithium silicate composite nano cooling promoter, the solution forms micro-scale turbulent disturbances near the heat exchange surface, which enhances heat transfer while preventing the nucleation and adhesion of crystals on the heat exchange plate surface. After being cooled by the heat exchanger, the solution temperature drops to 48°C and is then returned to the crystallization vessel. This circulation process is carried out continuously, keeping the solution temperature in the crystallization vessel decreasing uniformly at a rate of 3.5°C / h. S3. When the solution temperature in the crystallization vessel drops to 46℃, the solution state is monitored in real time using an online turbidity meter and a supersaturation detector. When the supersaturation of the solution reaches 1.03, 0.6g of potassium nitrate seed crystals with an average particle size of 85 mesh are added to the crystallization vessel. At the same time as adding the seed crystals, the stirring speed of the crystallization vessel is adjusted to a low-speed stirring mode of 90rpm, and the flow rate of the chilled water in the cooling circulation loop is adjusted simultaneously to control the solution cooling rate at 2.2℃ / h, maintaining the supersaturation of the solution within the metastable range of 1.01. This cooling process lasts for 2.8h, and the solution temperature gradually drops to 33℃. During this process, the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter significantly inhibits the adhesion and growth of crystals on the heat exchanger surface through the synergistic effect of microscale turbulence disturbance generated by its core-shell structure and surface hydrophilicity, while promoting the uniformity of crystal particle size distribution. S4. After step three is completed, the vacuum cooling system is activated to assist in cooling, controlling the vacuum degree inside the crystallization vessel to 1.1 kPa, so that the solution is further flash-cooled under vacuum conditions. The cooling rate is controlled at 1.2℃ / h until the solution temperature drops to 21℃. This temperature is maintained for continued crystallization and aging for 1.2h to allow potassium nitrate crystals to grow fully. The total time for the entire cooling and crystallization process is 9.5h. After crystallization, the crystal slurry is discharged and solid-liquid separation is performed by a centrifuge at a speed of 1300 rpm for 15 min. The separated solid is washed twice with 220g of ice water at 4℃ and then dried in a fluidized bed dryer at 82℃ until the moisture content is less than 0.2%, thus obtaining industrial-grade potassium nitrate product. Part of the separated mother liquor is recycled for the dissolution process in step one. The barium calcium zirconate titanate-lithium silicate composite nano cooling promoter remains stably dispersed during the mother liquor circulation process and can be reused for 3 batches before appropriate replenishment.

[0025] The preparation steps of the barium titanate-calcium silicate composite nano-cooling accelerator include: A1. Mix 5.8g zirconium tetrachloride, 8.6g tetrabutyl titanate, 8.3g barium nitrate, and 3.3g calcium nitrate. Dissolve the above raw materials in a mixed solvent of 82g anhydrous ethanol and 19g ethylene glycol methyl ether. The operation is carried out in a closed fume hood, with operators wearing gas masks and protective gloves. Stir at 300 rpm for 30 min at room temperature to form a homogeneous precursor solution. Then, transfer the precursor solution to a 200mL stainless steel autoclave lined with polytetrafluoroethylene, seal it, and place it in a constant temperature drying oven. Heat to 200℃ at a heating rate of 5℃ / min and maintain the temperature for 24 hours. h was subjected to solvothermal treatment, and after the reaction was completed, it was naturally cooled to room temperature. The precipitate was washed three times by alternating centrifugation with anhydrous ethanol and deionized water. Each centrifugation speed was 8000 rpm and the time was 15 min. The washed precipitate was collected and placed in a vacuum drying oven and dried at 80℃ for 12 h. The dried solid powder was transferred to a programmable muffle furnace and heated from room temperature to 500℃ at a heating rate of 2℃ / min and held at that temperature for 3 h. Then, the temperature was further increased to 850℃ at a heating rate of 2℃ / min and calcined for 6 h. Finally, it was naturally cooled to room temperature with the furnace to obtain barium calcium zirconate titanate nanocore particles with perovskite structure. In step A2, 5.1 g of the barium calcium zirconate titanate nanoparticles prepared in step A1 were ultrasonically dispersed in 152 g of anhydrous toluene at a power of 200 W for 30 min to form a uniform suspension. Then, 4.6 g of 3-aminopropyltriethoxysilane was added to the suspension to initiate the first stage of the reaction. The reaction was carried out at 80 °C for 6 h under nitrogen protection. After cooling, 3.3 g of γ-glycidyl etheroxypropyltrimethoxysilane was added, and the reaction was continued at 110 °C under reflux for 6 h. During the reaction, magnetic resonance was maintained. The stirring speed was 400 rpm. After the reaction was completed, the mixture was cooled to room temperature. The solid product was collected by centrifugation at 10,000 rpm for 20 min. The solid product was washed three times each with toluene, anhydrous ethanol and deionized water to remove unreacted silane coupling agent. The washed solid was placed in a vacuum drying oven at 60 °C and dried for 24 h to obtain modified nanoparticles with amino and epoxy bifunctional groups grafted on the surface. The silane coupling agent grafting density on the surface of the modified nanoparticles reached 2.1 mmol / g. A3. At room temperature, 3.1 g of the surface-functionalized modified nanoparticles prepared in step A2 were ultrasonically dispersed in a mixed solvent of 102 g anhydrous ethanol and 53 g deionized water. After ultrasonic treatment for 20 min, 1.9 g of cetyltrimethylammonium bromide (CTAB) with a purity of 99.0% was added as a template agent, and stirring was continued for 30 min until completely dissolved. Subsequently, 6.6 g of tetraethyl orthosilicate was slowly added dropwise as the main silicon source under vigorous stirring, while 2.9 g of lithium metasilicate tetrahydrate dissolved in 22 g of deionized water was added dropwise at a rate controlled at 0.5 mL / min. After the addition was completed, the pH of the system was adjusted with ammonia. To 9.8, the reaction was continued for 6 hours in a 40℃ water bath to carry out the sol-gel reaction. After the reaction was completed, the reaction system was transferred to a polytetrafluoroethylene-lined reactor and hydrothermally treated at 100℃ for 24 hours to promote the condensation and densification of the lithium silicate network. After cooling, the solid product was collected by centrifugation and washed three times each with anhydrous ethanol and deionized water. Then, the solid product was placed in a muffle furnace and calcined at 530℃ for 5 hours to remove the CTAB template agent, obtaining composite nanoparticles with a mesoporous lithium silicate shell coating. The shell thickness was 22nm, the pore diameter was 4.5nm, and the specific surface area reached 140m² / g. A4. The composite nanoparticles with mesoporous lithium silicate shells prepared in step A3 were immersed in a surface-hydrophilic modification solution prepared by 0.55g of γ-aminopropyltriethoxysilane, 0.35g of glacial acetic acid as a hydrolysis catalyst, and 21g of anhydrous ethanol. The solution was stirred at 50°C for 6h to carry out a sol-gel reaction. After centrifugation, the solids were washed three times with anhydrous ethanol. The washed solids were dried in a vacuum drying oven at 50°C for 12h and then heat-treated in a vacuum drying oven at 80°C for 4h to finally obtain a core-shell-dendritic structure barium titanate-lithium silicate composite nano-cooling promoter. Example 3

[0026] This embodiment provides a high-efficiency cooling process for potassium nitrate production, including the following steps: S1. 105g of industrial-grade crude potassium nitrate (92.8% potassium nitrate content) is added to 125g of deionized water and heated to 82℃ in a dissolving tank. The mixture is stirred at 280rpm for 30min to form a saturated potassium nitrate solution. Then, based on the mass of the industrial-grade crude potassium nitrate, 0.08g of barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is added. The mixture is dispersed in a high-shear emulsifier at 6000rpm for 15min to ensure that the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is uniformly dispersed in the potassium nitrate solution, forming a stable solid-liquid suspension system. The dispersed solution is filtered through a 100-mesh sieve to remove undissolved particles and then transferred to the pre-cooling crystallization system storage tank for later use. S2, the potassium nitrate solution containing barium calcium zirconate titanate-lithium silicate composite nano cooling promoter obtained in step S1 is pumped into the external circulation cooling loop at a flow rate of 100 m³ / h. The core equipment of this cooling loop is a detachable spiral plate heat exchanger with a heat exchange area of ​​55 m². The cooling medium of the heat exchanger is chilled water with a circulation rate of 12°C. The potassium nitrate solution passes through the spiral plate heat exchanger at a flow rate of 1.7 m / s. Under the action of the barium calcium zirconate titanate-lithium silicate composite nano cooling promoter, the solution forms micro-scale turbulent disturbances near the heat exchange surface, which enhances heat transfer while preventing the nucleation and adhesion of crystals on the heat exchange plate surface. After being cooled by the heat exchanger, the solution temperature drops to 52°C and is then returned to the crystallization vessel. This circulation process is carried out continuously, keeping the solution temperature in the crystallization vessel decreasing uniformly at a rate of 4.5°C / h. S3. When the solution temperature in the crystallization vessel drops to 49℃, the solution state is monitored in real time using an online turbidity meter and a supersaturation detector. When the supersaturation of the solution reaches 1.05, 0.9g of potassium nitrate seed crystals with an average particle size of 95 mesh are added to the crystallization vessel. At the same time as adding the seed crystals, the stirring speed of the crystallization vessel is adjusted to a low-speed stirring mode of 110rpm, and the flow rate of the chilled water in the cooling circulation loop is adjusted simultaneously to control the solution cooling rate at 2.8℃ / h, maintaining the supersaturation of the solution within the metastable range of 1.03. This cooling process lasts for 3.2h, and the solution temperature gradually drops to 37℃. During this process, the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter significantly inhibits the adhesion and growth of crystals on the heat exchanger surface through the synergistic effect of microscale turbulence disturbance generated by its core-shell structure and surface hydrophilicity, while promoting the uniformity of crystal particle size distribution. S4. After step S3 is completed, the vacuum cooling system is activated to assist in cooling, controlling the vacuum degree inside the crystallization vessel to 1.4 kPa, so that the solution is further flash-cooled under vacuum conditions. The cooling rate is controlled at 1.8℃ / h until the solution temperature drops to 24℃. This temperature is maintained for continued crystallization and aging for 1.5h to allow potassium nitrate crystals to grow fully. The total time for the entire cooling and crystallization process is 11h. After crystallization, the crystal slurry is discharged and solid-liquid separation is performed by a centrifuge at a speed of 1400 rpm for 15 min. The separated solid is washed twice with 280g of ice water at 6℃ and then dried in a fluidized bed dryer at 88℃ until the moisture content is less than 0.2%, thus obtaining industrial-grade potassium nitrate product. Part of the separated mother liquor is recycled for the dissolution process in step one. The barium calcium zirconate titanate-lithium silicate composite nano cooling promoter remains in a stable dispersion state during the mother liquor circulation process and can be reused for 5 batches before appropriate replenishment.

[0027] The preparation steps of the aforementioned barium titanate-lithium silicate composite nano-cooling accelerator include: A1, mixing 6.2g zirconium tetrachloride, 8.2g tetrabutyl titanate, 8.1g barium nitrate, and 3.1g calcium nitrate; dissolving the above raw materials in a mixed solvent of 78g anhydrous ethanol and 21g ethylene glycol methyl ether; the operation is carried out in a closed fume hood, with operators wearing gas masks and protective gloves; stirring at 300rpm for 30min at room temperature to form a homogeneous precursor solution; then transferring the precursor solution to a 200mL polytetrafluoroethylene-lined stainless steel high-pressure reactor; sealing and placing it in a constant temperature drying oven; and heating at a rate of 5℃ / min. The mixture was heated to 200℃ and kept at that temperature for 24 hours for solvothermal treatment. After the reaction, it was naturally cooled to room temperature. The precipitate was washed three times by alternating centrifugation with anhydrous ethanol and deionized water. Each centrifugation was performed at 8000 rpm for 15 minutes. The washed precipitate was collected and placed in a vacuum drying oven and dried at 80℃ for 12 hours. The dried solid powder was transferred to a programmable muffle furnace and heated from room temperature to 500℃ at a heating rate of 2℃ / min and held for 3 hours. Then, the temperature was further increased to 850℃ at a heating rate of 2℃ / min and calcined for 6 hours. Finally, it was naturally cooled to room temperature with the furnace to obtain barium calcium zirconate titanate nanocore particles with a perovskite structure. A2, 4.9g of the barium calcium zirconate titanate nanoparticles prepared in step A1 were ultrasonically dispersed in 148g of anhydrous toluene at a power of 200W for 30min to form a uniform suspension. Then, 4.4g of 3-aminopropyltriethoxysilane (APTES, purity 98.0%) was added to the suspension to initiate the first stage of the reaction. The reaction was carried out at 80℃ for 6h under nitrogen protection. After cooling, 3.1g of γ-glycidyl etheroxypropyltrimethoxysilane (KH-560, purity 960) was added. 98.0%, and continue to reflux at 110℃ for 6h. During the reaction, the magnetic stirring speed is maintained at 400rpm. After the reaction, the mixture is cooled to room temperature, and the solid product is collected by centrifugation at 10000rpm for 20min. The solid product is washed three times each with toluene, anhydrous ethanol and deionized water to remove unreacted silane coupling agent. The washed solid is placed in a vacuum drying oven at 60℃ and dried for 24h to obtain modified nanoparticles with amino and epoxy bifunctional groups grafted on the surface. A3. At room temperature, 2.9 g of the surface-functionalized modified nanoparticles prepared in step A2 were ultrasonically dispersed in a mixed solvent of 98 g anhydrous ethanol and 51 g deionized water. After ultrasonic treatment for 20 min, 1.7 g of hexadecyltrimethylammonium bromide was added as a template agent, and stirring was continued for 30 min until completely dissolved. Subsequently, 6.2 g of tetraethyl orthosilicate was slowly added dropwise as the main silicon source under vigorous stirring, while 2.7 g of metasilicic acid tetrahydrate dissolved in 18 g of deionized water was added dropwise at a rate controlled at 0.5 mL / min. After the addition was complete... The pH of the system was then adjusted to 9.8 using ammonia. The reaction was continued for 6 hours in a 40°C water bath to carry out the sol-gel reaction. After the reaction was completed, the reaction system was transferred to a polytetrafluoroethylene-lined reactor and subjected to hydrothermal treatment at 100°C for 24 hours to promote the condensation and densification of the lithium silicate network. After cooling, the solid product was collected by centrifugation and washed three times each with anhydrous ethanol and deionized water. The solid product was then placed in a muffle furnace and calcined at 530°C for 5 hours to remove the CTAB template agent, thus obtaining composite nanoparticles with a mesoporous lithium silicate shell coating. A4. The composite nanoparticles with mesoporous lithium silicate shells prepared in step A3 were immersed in a surface-hydrophilic modification solution prepared by 0.45 g γ-aminopropyltriethoxysilane, 0.25 g glacial acetic acid as a hydrolysis catalyst, and 19 g anhydrous ethanol. The solution was stirred at 50 °C for 6 h to carry out a sol-gel reaction. After centrifugation, the solid was washed three times with anhydrous ethanol. The washed solid was dried in a vacuum drying oven at 50 °C for 12 h, and then heat-treated in a vacuum drying oven at 80 °C for 4 h to finally obtain a core-shell-dendritic structure barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter.

[0028] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator is not added in step S1. The remaining process parameters are the same as in Example 1.

[0029] Comparative Example 2 The specific implementation method is the same as in Example 1, except that potassium nitrate seed crystals are not added in step S3. The remaining process parameters are the same as in Example 1.

[0030] Comparative Example 3 The specific implementation method is the same as in Example 1, except that the barium calcium zirconate titanate-lithium silicate composite nano cooling promoter is replaced with barium calcium zirconate titanate nano core particles without lithium silicate shell, that is, it is used directly after only completing step A1.

[0031] Performance testing The high-efficiency cooling process for potassium nitrate production described in Examples 1-3 and Comparative Examples 1-3 was tested for performance according to the following method, which includes the following steps: Test method for heat transfer coefficient retention rate: During continuous operation in step S2, a platinum resistance temperature sensor with an accuracy of 0.1℃ and an electromagnetic flowmeter with an accuracy of 0.5% are installed at the inlet and outlet of the hot and cold fluids of the spiral plate heat exchanger, respectively. The data acquisition system records the temperature and flow rate values ​​every 30 seconds. The overall heat transfer coefficient K is calculated according to the formula K=Q / A×ΔTm, where Q is the heat transfer capacity in W, Q=cp×m×ΔT, cp is the specific heat capacity of potassium nitrate solution (taken as 3.2kJ / (kg·℃), m is the mass flow rate in kg / s, ΔT is the temperature difference between the inlet and outlet of potassium nitrate solution in ℃; A is the heat exchange area (taken as 50m²); ΔTm is the logarithmic mean temperature difference in ℃, ΔTm=(ΔT1-ΔT2) / ln(ΔT1 / ΔT2), where ΔT1 is the difference between the inlet temperature of the hot fluid and the outlet temperature of the cold fluid, and ΔT2 is the difference between the outlet temperature of the hot fluid and the inlet temperature of the cold fluid. The total heat transfer coefficients K0 and K24 were recorded at the initial time t=0h and after continuous operation for 24h, respectively. The heat transfer coefficient retention rate was calculated as K24 / K0×100%. Each example and comparative example was measured three times and the arithmetic mean was taken.

[0032] Scale evaluation method: After continuous operation for 24 hours in step S2, the system is shut down, the detachable spiral plate heat exchanger is disassembled, and the heat exchange plates are removed. Using a coating thickness gauge with an accuracy of 0.01 mm, 20 measurement points are evenly selected on the surface of the heat exchange plates to measure the scale layer thickness, and the average thickness is calculated. Simultaneously, the scale layer coverage is observed using a digital microscope at 50x magnification, and the percentage of scale layer coverage area to the total area of ​​the heat exchange plates is calculated using image analysis software. A scale layer coverage area ≤ 5% and an average thickness ≤ 0.05 mm is evaluated as no obvious scale layer; a scale layer coverage area 5%-15% and an average thickness 0.05-0.15 mm is evaluated as a small amount of scale layer; and a scale layer coverage area > 15% or an average thickness > 0.15 mm is evaluated as an obvious scale layer.

[0033] Product crystal particle size distribution test method: Take 50g of potassium nitrate product dried in step S4 and determine its particle size distribution using a laser particle size analyzer. The test adopts a dry dispersion mode, with the dispersion pressure set to 0.3MPa, the injection speed set to 50%, the refractive index set to 1.53, the absorptivity set to 0.01, the measurement range set to 0.1μm to 1000μm, the background measurement time set to 10s, and the sample measurement time set to 10s. Each sample is measured three times consecutively, and the arithmetic mean is taken. Record the particle size values ​​D10, D50, and D90 corresponding to the cumulative volume fraction reaching 10%, 50%, and 90%, in μm. Calculate the particle size distribution width parameter according to the formula Span = (D90 - D10) / D50. The smaller the Span value, the more concentrated the particle size distribution.

[0034] Product purity test method: The potassium nitrate content is determined using the sodium tetraphenylborate gravimetric method. Weigh 5.000 g of the sample dried to constant weight, accurate to 0.001 g, place it in a 250 mL beaker, add 100 mL of deionized water, heat and stir until completely dissolved, and cool to room temperature. Add 10 mL of sodium tetraphenylborate solution, stir and let stand for 30 min to allow complete precipitation. Filter the precipitate using a pre-weighed G4 sintered sand crucible, wash the precipitate 5 times with 10 mL of deionized water each time, and place the crucible and precipitate in a 105℃ oven to dry to constant weight, weighing to 0.001 g. Calculate the potassium nitrate mass fraction using the following formula: KNO3 content % = m1 × 0.2822 / m × 100%, where m1 is the mass of the potassium tetraphenylborate precipitate in g, 0.2822 is the conversion factor from potassium tetraphenylborate to potassium nitrate, and m is the sample mass in g. Chloride content was determined by silver nitrate titration method, moisture content was determined by Karl Fischer coulometric method, and water-insoluble matter content was determined by gravimetric method. 50g of sample was weighed and dissolved in 200mL of deionized water, filtered through a pre-weighed G4 sintered sand crucible, dried at 105℃ to constant weight, and then weighed for calculation.

[0035] Method for testing the dispersion stability of barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerator: Take 0.100 g each of the barium calcium zirconate titanate-lithium silicate composite nano-cooling accelerators prepared in Examples 1-3 and Comparative Example 3, and place them in 100 mL volumetric flasks respectively. Add saturated potassium nitrate solution to make up to 100 mL. Disperse using ultrasound at 200 W power, 40 kHz frequency, and 10 min to obtain a suspension with a concentration of 1.0 g / L. Transfer the suspension to a 100 mL stoppered graduated cylinder and let it stand for 24 h at room temperature (25 °C). Take approximately 10 mL of the upper layer suspension after 24 h of standing and measure the Zeta potential value using a Zeta potential analyzer at 25 °C. Measure each sample three times and take the arithmetic mean. Simultaneously observe and record the volume of precipitate at the bottom of the graduated cylinder, and calculate the precipitate volume percentage = precipitate volume / 100 mL × 100%.

[0036] Supersaturation control accuracy test method: During the cooling and crystallization process in step S3, the supersaturation value of the solution was continuously monitored using an online supersaturation detector. The supersaturation detector adopted the conductivity method, and the supersaturation S=C / C was obtained by measuring the conductivity of the solution, where C is the real-time concentration of the solution and C is the saturation concentration at the same temperature. The data acquisition system recorded the supersaturation value at a sampling frequency of 1 time / min, and the entire cooling stage lasted for 3.0 hours, collecting a total of 180 data points. Using a set supersaturation of 1.02 as a benchmark, the absolute value of the deviation for each data point was calculated. The average deviation was calculated according to the formula Σ|Si-1.02| / 180, and the maximum deviation was calculated according to the formula max|Si-1.02|.

[0037] Product yield test method: Based on the mass of industrial-grade crude potassium nitrate added in step S1, calculate the percentage of the final product mass to the theoretical product mass. The theoretical product mass is calculated based on 100% conversion of KNO3 content in the crude potassium nitrate. Product yield % = Actual dried product mass / Mass of industrial-grade crude potassium nitrate × 100%. Each example and comparative example was measured three times, and the arithmetic mean was taken.

[0038] Test results:

[0039] As can be seen from Table 1, Examples 1-3 show significant advantages over Comparative Examples 1-3 in several key performance indicators, systematically solving the technical problems existing in the current potassium nitrate cooling crystallization process, such as easy scaling of heat exchangers, low cooling efficiency, high energy consumption, and uneven crystal particle size distribution.

[0040] Specifically, regarding the scale prevention and heat transfer efficiency of heat exchangers, Comparative Example 1, lacking the addition of barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter, had a heat transfer coefficient retention rate of only 81.6%. After 24 hours of operation, a significant scale layer appeared on the heat exchange surface, indicating that traditional processes suffer from severe scale buildup in the absence of effective scale prevention measures, leading to a significant decrease in heat transfer efficiency, which in turn results in increased cooling energy consumption and reduced production efficiency. In contrast, Comparative Example 3, although containing barium calcium zirconate titanate nano-core particles without a lithium silicate shell, saw its heat transfer coefficient retention rate increase to 92.0%, but a small amount of scale layer still appeared. This indicates that while single nano-core particles have a certain heat transfer enhancement effect, the lack of hydrophilicity and microscale turbulence disturbance enhancement provided by the lithium silicate shell makes it impossible to completely suppress the adhesion of crystals on the heat exchange surface.

[0041] In contrast, Examples 1-3, which used barium calcium zirconate titanate-lithium silicate composite nano-cooling promoters, achieved a heat transfer coefficient retention rate as high as 98.4-98.8%. After 24 hours of continuous operation, no obvious scale layer was observed on the heat exchange surface. This demonstrates that the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoters, through the synergistic effect of microscale turbulence disturbances generated by their unique core-shell structure and surface hydrophilicity, significantly inhibited the nucleation and adhesion of crystals on the heat exchanger surface, thereby solving the problem of cooling efficiency decay and increased energy consumption caused by easy scaling of heat exchangers.

[0042] Regarding the uniformity of crystal particle size distribution, Comparative Example 1 did not add the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter and exhibited significant scaling. Its product had a D50 of only 135 μm and a Span value as high as 1.81, with an extremely wide particle size distribution. Comparative Example 2, although it added the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter, did not add crystal seeds. The average deviation of supersaturation reached 0.042, and the maximum deviation reached 0.085, exceeding the metastable region and causing explosive nucleation. The product had a D50 of 142 μm but a Span value of 1.34, and the particle size distribution was also uneven. Moreover, the product yield was only 92.8%, the lowest among all comparative examples. Comparative Example 3 used particles without a lithium silicate shell, and the product had a D50 of 165 μm and a Span value of 0.73. The particle size distribution was still wider than that of the examples. In Examples 1-3, under strict control of supersaturation, the average deviation of supersaturation was only 0.008-0.010, and the maximum deviation did not exceed 0.022. The product D50 was stable between 172-185 μm, and the Span value was controlled within a narrow range of 0.60-0.64. This indicates that under the microscale turbulent disturbance of the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter, combined with precise timing of seed addition and supersaturation control, potassium nitrate crystals can grow uniformly along specific crystal planes to form a regular hexagonal prism morphology, effectively solving the problem of uneven crystal particle size distribution in traditional processes.

[0043] Regarding product purity and yield, the purity of the products in Examples 1-3 all reached over 99.5%, significantly higher than that of Comparative Example 1 (99.2%), Comparative Example 2 (99.0%), and Comparative Example 3 (99.4%). The product yield also reached 95.8-96.5%, which was better than that of Comparative Example 1 (94.5%), Comparative Example 2 (92.8%), and Comparative Example 3 (95.2%). This is attributed to the stable dispersion of the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter during the mother liquor circulation process. Its absolute value of the Zeta potential reached 34-36mV, while that of Comparative Example 3 was only -18mV. This proves that the introduction of the lithium silicate shell significantly improved the dispersion stability of the nanoparticles in the potassium nitrate saturated solution, allowing it to be reused 3-5 times, further reducing the process cost.

[0044] In summary, Examples 1-3, through optimized design of the core-shell structure of the barium calcium zirconate titanate-lithium silicate composite nano-cooling promoter and precise control of cooling crystallization process parameters, comprehensively outperform the comparative examples in terms of heat exchanger anti-fouling performance, heat transfer efficiency, uniformity of crystal particle size distribution, product purity, and yield. They effectively solve the technical problems of low cooling crystallization efficiency, high energy consumption, uneven crystal particle size distribution, and easy fouling of heat exchangers in the prior art.

[0045] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-efficiency cooling process for potassium nitrate production, characterized in that, Includes the following steps: S1, by weight, add 90-110 parts of crude potassium nitrate to 110-130 parts of deionized water, heat to 75-85℃, stir, add 0.05-0.15 parts of barium calcium zirconate titanate-lithium silicate composite nano cooling promoter, shear and disperse to obtain a dispersed solution. S2, the dispersed solution is pumped into a heat exchanger for cooling, and then returned to the crystallization vessel; S3, when the temperature of the dispersed solution in the crystallization vessel drops to 45-50℃, add 0.5-1.0 parts of potassium nitrate seed crystals to the crystallization vessel and cool; S4. Start the vacuum cooling system to assist in cooling down until the temperature drops to 20-25℃, crystallization and aging occur. After crystallization is complete, discharge the crystal slurry, centrifuge to separate it, and obtain the solid. Wash the solid with ice water at 4-6℃ and dry it in a fluidized bed dryer at 80-90℃.

2. The high-efficiency cooling process for potassium nitrate production according to claim 1, characterized in that, In step S1, the shear dispersion time is 10-20 min.

3. The high-efficiency cooling process for potassium nitrate production according to claim 1, characterized in that, In step S2, the temperature is cooled to 45-55°C.

4. The high-efficiency cooling process for potassium nitrate production according to claim 1, characterized in that, In step S3, the temperature is cooled to 32-38°C.

5. The high-efficiency cooling process for potassium nitrate production according to claim 1, characterized in that, In step S4, the crystallization aging time is 1.0-2.0 h.

6. The high-efficiency cooling process for potassium nitrate production according to any one of claims 1-5, characterized in that, The preparation steps of the barium titanate-calcium silicate composite nano-cooling accelerator include: A1, by weight, 5.8-6.2 parts of zirconium tetrachloride and 8.2-8.6 parts of tetrabutyl titanate are mixed. First, 8.0-8.5 parts of barium nitrate and 3.0-3.5 parts of calcium nitrate are dissolved in a mixed solvent of 75-85 parts of anhydrous ethanol and 18-22 parts of ethylene glycol methyl ether to obtain solution A. Zirconium tetrachloride and tetrabutyl titanate are added to solution A and stirred at room temperature to obtain a precursor solution. The precursor solution is transferred to a reaction vessel, sealed, and placed in a constant temperature drying oven. The temperature is raised to 195-205℃ for a solvothermal reaction. After the reaction is completed, it is naturally cooled to room temperature to obtain a precipitate. The precipitate is washed with anhydrous ethanol and deionized water and vacuum dried to obtain a dried solid. The dried solid is transferred to a muffle furnace and calcined at 495-505℃, then calcined at 845-855℃, and cooled to room temperature with the furnace to obtain barium calcium zirconate titanate nanocore particles. A2. Barium calcium zirconate titanate nanoparticles were ultrasonically dispersed in 145-155 parts of anhydrous toluene to obtain a suspension. Then, 4.3-4.7 parts of 3-aminopropyltriethoxysilane were added to the suspension sequentially. Under nitrogen protection, the reaction was carried out at 78-82℃. After cooling, 3.0-3.4 parts of γ-glycidoxypropyltrimethoxysilane were added, and the temperature was further increased to 108-112℃ for reflux reaction. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed with toluene, anhydrous ethanol, and deionized water to obtain the washed solid. The washed solid was dried in a vacuum drying oven at 58-62℃ to obtain modified nanoparticles with amino and epoxy bifunctional groups grafted on the surface. A3, at room temperature, ultrasonically disperse 2.8-3.2 parts of modified nanoparticles with amino and epoxy bifunctional groups grafted onto their surface in a mixed solvent of 95-105 parts anhydrous ethanol and 50-55 parts deionized water. After ultrasonic treatment, add 1.6-2.0 parts of hexadecyltrimethylammonium bromide, continue stirring, and dropwise add 6.0-7.0 parts of tetraethyl orthosilicate. Simultaneously, dropwise add 2.6-3.0 parts of lithium metasilicate tetrahydrate dissolved in 15-25 parts of deionized water. After the addition is complete... Afterwards, the pH was adjusted to 9.5-10.0, and the reaction was continued to be stirred in a water bath at 38-42℃ to obtain a reaction mixture. The reaction mixture was transferred to a reaction vessel and subjected to hydrothermal treatment at 98-102℃. After cooling, the mixture was centrifuged to collect the solid product. The solid product was washed with anhydrous ethanol and deionized water to obtain the washed solid product. The washed solid product was placed in a muffle furnace and calcined at 520-540℃ to obtain composite nanoparticles coated with lithium silicate shell. A4. The composite nanoparticles coated with lithium silicate shells are immersed in a solution of 0.4-0.6 parts γ-aminopropyltriethoxysilane, 0.2-0.4 parts glacial acetic acid, and 18-22 parts anhydrous ethanol. The mixture is stirred and reacted at 48-52℃, centrifuged, and the solid product is collected. The solid product is washed with anhydrous ethanol to obtain the washed solid. The washed solid is dried in a vacuum drying oven at 48-52℃ and then heat-treated in a vacuum drying oven at 78-82℃.

7. The high-efficiency cooling process for potassium nitrate production according to claim 6, characterized in that, In step A1, the calcination time at 845-855℃ is 6-8 hours.

8. The high-efficiency cooling process for potassium nitrate production according to claim 6, characterized in that, In step A2, the reflux reaction time at 108-112℃ is 6-8 hours.

9. The high-efficiency cooling process for potassium nitrate production according to claim 6, characterized in that, In step A3, the hydrothermal treatment at 98-102℃ takes 24-30 hours.

10. The high-efficiency cooling process for potassium nitrate production according to claim 6, characterized in that, In step A4, the reaction is stirred at 48-52℃ for 6-8 hours.

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