A droplet polarization atomization low-temperature spray drying system and method based on coulomb field effect

Abstract

The application belongs to the technical field of spray drying, and discloses a liquid drop polarization atomization low-temperature spray drying system and method based on a coulomb field effect. The system comprises a feed liquid supply unit, an atomization nozzle, a high-voltage polarization electrode unit, a high-voltage power supply, a drying tower and a low-temperature nitrogen circulation drying unit. The high-voltage polarization electrode unit comprises at least one electrode ring or a conical ring electrode arranged coaxially below the nozzle outlet and kept at a non-contact gap with the nozzle outlet. After the feed liquid is preliminarily atomized by the nozzle, the liquid drops pass through the coulomb field area generated by the electrode ring under the action of gravity, are further split and dispersed into a polarized drop group with smaller particle size and more uniform distribution through the dielectric polarization effect, and the spontaneous formation of the microcapsule shell-core structure is promoted. The liquid drops are electrically neutral or close to electrically neutral, thereby avoiding electrostatic adsorption and wall sticking. The application is particularly suitable for the low-temperature spray drying preparation of heat-sensitive materials and microcapsule products.

Description

Technical Field

[0001] This invention belongs to the field of spray drying technology, specifically relating to a droplet polarization atomization low-temperature spray drying system and method based on the Coulomb field effect, which is particularly suitable for low-temperature drying of heat-sensitive materials and preparation of microcapsule-encapsulated products. Background Technology

[0002] Spray drying technology is a widely used method for preparing powder materials in the food, pharmaceutical, chemical, and ceramics industries. Its basic principle is to disperse liquid materials into tiny droplets through an atomizer, causing the solvent to evaporate rapidly in a hot drying medium, thereby obtaining a powdered or granular product. Traditional spray drying technology typically uses high-temperature hot air as the drying medium, with inlet temperatures generally ranging from 150℃ to 350℃ and outlet temperatures typically from 60℃ to 120℃. While these high-temperature operating conditions are feasible for materials with good thermal stability, they can cause severe loss of activity and quality degradation for heat-sensitive materials with biological activity.

[0003] With the rapid development of fields such as biomedicine, functional foods, and fine chemicals, a large number of heat-sensitive materials require spray drying and microencapsulation. For example, probiotic live bacteria preparations have extremely low survival rates at high temperatures; enzyme preparations rapidly inactivate at temperatures exceeding 60°C; vaccines and bioactive proteins have intricate three-dimensional structures, and high temperatures can cause protein denaturation and aggregation; oils rich in unsaturated fatty acids are prone to oxidative rancidity at high temperatures; and volatile flavorings and fragrances lose their characteristic aroma components at high temperatures. The drying problem of these heat-sensitive materials has become a key technological bottleneck restricting the development of related industries.

[0004] To overcome the shortcomings of high-temperature drying, those skilled in the art have developed low-temperature spray drying and freeze-spray drying technologies. The core idea is to use a low-temperature drying medium (such as chilled nitrogen or low-temperature dehumidified air) to replace high-temperature hot air, reducing the temperature of the drying medium to room temperature or even sub-zero temperatures. However, the core challenge of low-temperature drying lies in the significant reduction in the drying driving force (temperature difference), leading to a substantial decrease in the solvent evaporation rate and a prolonged drying time. To address this issue, it is necessary to maximize the specific surface area of ​​the droplets during the atomization process, i.e., to generate smaller and more numerous droplets at the same volumetric flow rate, in order to compensate for the insufficient mass and heat transfer efficiency under low-temperature conditions.

[0005] Currently, there are three main atomization methods used in industry: pressure atomization, centrifugal atomization, and two-fluid airflow atomization. Pressure atomization uses a high-pressure pump to pressurize the liquid and eject it from a nozzle orifice, converting pressure energy into kinetic energy to achieve atomization. Its disadvantages include a wide droplet size distribution and poor atomization effect for high-viscosity liquids. Centrifugal atomization uses a high-speed rotating atomizing disc to throw the liquid out, overcoming surface tension through centrifugal force to achieve atomization. Its advantages include high throughput, but the equipment structure is complex, energy consumption is high, and droplet size adjustment is not flexible enough. Two-fluid airflow atomization uses a high-speed airflow to mix with the liquid inside the nozzle or at the outlet, tearing the liquid into fine droplets through airflow shear force. Its atomization effect is greatly affected by the gas-liquid ratio, and energy consumption is relatively high. All three of these traditional atomization methods struggle to simultaneously achieve fine droplet size (usually less than 30 μm) and low energy consumption under low-temperature conditions, failing to fully compensate for the insufficient mass and heat transfer efficiency during low-temperature drying.

[0006] To overcome the aforementioned technical limitations, electrostatic spraying technology offers a new solution for low-temperature spray drying. Its basic principle is to apply a high-voltage electrostatic field to the atomization zone, causing the droplets to carry a charge. The Coulomb repulsion force between these charges overcomes the surface tension of the liquid, achieving further breakup and dispersion of the droplets. Existing electrostatic spraying technologies are mainly divided into the following two categories:

[0007] The first type is contact-charged electrostatic spraying. As disclosed in US Patent 10286411, a high-voltage electrode is placed directly inside the nozzle in contact with the liquid, and the liquid becomes charged through contact conduction. When the liquid flows inside the nozzle, it comes into direct contact with the high-voltage electrode, acquires a net charge, and is then sprayed out of the nozzle. Because the droplets carry the same charge, they are further dispersed under the action of Coulomb repulsion. While this approach can achieve droplet charging and secondary dispersion, it suffers from the following serious drawbacks: First, the high-voltage electrode is in direct contact with the feed solution, making the electrode surface susceptible to contamination and corrosion from solids, salts, and organic matter in the solution. This affects electrode lifespan and spray stability. Furthermore, for continuous industrial production, the electrode requires frequent cleaning and maintenance, increasing downtime and production costs. Second, for microcapsule encapsulation solutions containing sensitive core materials (such as probiotics, enzymes, vaccines, and active proteins), contact-type high-voltage charging can generate a strong local electric field and potential electrochemical reactions within the liquid. The resulting heat and free radicals can damage the shell-core structure of the microcapsules, leading to core material leakage, decreased encapsulation efficiency, and loss of activity. Third, the direct application of high voltage to the feed solution may trigger electrochemical reactions, altering the pH, ionic strength, and component structure of the solution, resulting in irreversible changes in material properties.

[0008] The second type is electrostatic spraying using inductive charging or corona discharge. For example, the dual electrostatic spraying device disclosed in Chinese patent CN205628359U employs a three-channel coaxial structure, with the outermost layer being an electrode sleeve. The droplets are charged through corona discharge or induction. However, this approach has the following drawbacks: the electrode sleeve is still located in the annular channel inside the nozzle, separated from the liquid only by an insulating medium. Essentially, it remains a quasi-contact charging mode, and the high electric field strength may still penetrate the insulating layer and affect the liquid. The arrangement of the electrode sleeve limits the flexibility of the nozzle structure, making it difficult to adapt to the electrode parameter adjustment requirements of different material properties and process conditions. Furthermore, this approach is mainly aimed at small-scale synthesis devices for metal-organic framework (MOF) materials and does not involve the overall design of industrial-grade low-temperature spray drying systems, nor the integration of low-temperature nitrogen circulation drying units and solvent recovery systems.

[0009] Furthermore, in the aforementioned existing electrostatic spraying technology, the droplets acquire a net charge through contact conduction or induction, meaning each droplet carries a certain amount of excess positive or negative charge. When these charged droplets move within the drying tower, due to the repulsive force between like charges, they tend to drift and deposit on the tower wall, leading to severe product adhesion problems. This not only reduces product yield but also increases the difficulty and frequency of equipment cleaning. Simultaneously, droplets carrying a net charge may experience corona discharge or breakdown discharge within the drying tower, posing safety hazards.

[0010] In view of the multiple shortcomings of the existing technologies, especially the special requirements of microcapsule encapsulation and drying processes under low temperature conditions, there is an urgent need in the field for an electrostatic spray drying technology that can achieve efficient polarization dispersion of droplets under non-contact conditions, while maintaining the complete microcapsule shell-core structure, avoiding adhesion of charged droplets to the tower wall, and is compatible with low temperature nitrogen circulation drying systems. Summary of the Invention

[0011] The purpose of this invention is to overcome the above-mentioned shortcomings in the prior art and provide a droplet polarization atomization low-temperature spray drying system and method based on the Coulomb field effect, which can avoid direct contact between the electrode and the liquid, maintain the integrity of the liquid and the microcapsule structure therein, and achieve efficient drying under low-temperature conditions.

[0012] The core solution of this invention is to further split and disperse the droplets by coaxially arranging a high-voltage electrode ring or a conical ring electrode below the atomizing nozzle outlet and maintaining a non-contact gap with the nozzle outlet, and utilizing the dielectric polarization effect of the Coulomb electric field on the droplets. At the same time, the directional migration of polar molecules in the electric field promotes the spontaneous formation of the microcapsule shell-core structure.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] The first aspect of the present invention is to provide a droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect, comprising:

[0015] The liquid supply unit is used to deliver the liquid to be dried to the atomizing nozzle;

[0016] Atomizing nozzles, with their nozzle outlets facing downwards, are used to initially atomize the liquid material into initial droplets;

[0017] A high-voltage polarized electrode unit includes at least one electrode ring or conical ring electrode, which is coaxially arranged below the nozzle outlet of the atomizing nozzle and maintains a non-contact gap with the nozzle outlet, for generating a Coulomb electric field in the atomization region below the nozzle outlet.

[0018] A high-voltage power supply, electrically connected to the high-voltage polarized electrode unit, is used to apply high-voltage direct current to the electrode ring or conical ring electrode;

[0019] The drying tower, whose upper part is connected to the atomizing nozzle, is used to contain the atomized droplets after polarization treatment by the high-voltage polarized electrode unit and to contact the low-temperature drying medium to complete the drying.

[0020] A low-temperature nitrogen circulating drying unit is connected to the drying tower and is used to supply low-temperature drying nitrogen to the drying tower and recycle it.

[0021] Preferably, the high-voltage polarized electrode unit comprises a single electrode ring, wherein:

[0022] The inner diameter of the electrode ring is 2 to 10 times the outlet diameter of the atomizing nozzle;

[0023] The non-contact gap d between the electrode ring and the outlet of the atomizing nozzle is 5mm to 100mm, preferably 10mm to 50mm.

[0024] More preferably, the voltage applied by the high-voltage power supply to the electrode ring or the conical ring electrode is ±5kV to ±100kV, more preferably ±10kV to ±60kV, and even more preferably ±20kV to ±50kV.

[0025] More preferably, the high-voltage polarization electrode unit includes multiple electrode rings arranged at intervals along the vertical direction, forming a multi-ring stepped electrode group, wherein:

[0026] The spacing between adjacent electrode rings is 5mm to 80mm, and the diameter of each electrode ring increases or decreases from top to bottom.

[0027] More preferably, each electrode ring in the multi-ring stepped electrode group is powered by the same high-voltage power supply or by an independently regulated high-voltage power supply, wherein:

[0028] The voltage difference between adjacent electrode rings forms a gradient Coulomb field, causing the droplet to experience a gradually changing polarization electric field during its descent.

[0029] More preferably, the high-voltage polarization electrode unit includes one of the conical ring electrodes, wherein:

[0030] The inner diameter of the conical ring electrode gradually increases or decreases from top to bottom, and its cone angle α is 5°~60°, preferably 10°~45°. The axial height of the conical ring electrode is 20mm~150mm.

[0031] More preferably, the electrode ring or the conical ring electrode is made of a conductive metal material, wherein the conductive metal material is selected from stainless steel, titanium alloy, or brass, wherein:

[0032] The surface of the electrode ring or the conical ring electrode is provided with an insulating coating, which is a polytetrafluoroethylene coating or a ceramic coating, and the thickness of the insulating coating is 0.05 mm to 2 mm.

[0033] More preferably, the low-temperature nitrogen circulating drying unit includes:

[0034] A nitrogen heater / cooler is used to adjust the circulating nitrogen to a target drying temperature, which is -20°C to 100°C, preferably 0°C to 60°C.

[0035] A nitrogen circulation fan is used to drive the circulation of nitrogen within the system.

[0036] A gas-solid separation device is used to separate dried powder particles from nitrogen gas;

[0037] Solvent recovery condenser, used to condense and recover evaporated solvent carried in nitrogen gas; and

[0038] Adsorption dryers are used for deep dehumidification of condensed nitrogen gas.

[0039] A second aspect of the present invention is to provide a method for low-temperature spray drying of droplet polarization atomization based on the Coulomb field effect, employing the system described in any of the above claims, comprising the following steps:

[0040] S1. The liquid material to be dried is pumped to the atomizing nozzle and initially atomized by the nozzle to form initial droplets.

[0041] S2. The initial droplet is allowed to pass through the Coulomb electric field region generated by the electrode ring or conical ring electrode arranged below the nozzle outlet under the action of gravity. Under the action of the Coulomb electric field, the droplet undergoes dielectric polarization, and the polar molecules inside the droplet are oriented and aligned along the direction of the electric field, inducing a polarized charge distribution on the droplet surface. The Coulomb repulsion force generated by the polarized charge overcomes the surface tension of the liquid, causing the droplet to further split and disperse into a group of polarized droplets with smaller particle size and more uniform distribution. At the same time, for microcapsule liquid containing shell material and core material, the Coulomb electric field causes the polar molecules of the shell material to be oriented and enriched towards the droplet surface, and the non-polar molecules of the core material to tend towards the interior of the droplet, spontaneously forming a shell-core microcapsule structure.

[0042] S3. The polarized droplet group comes into contact with low-temperature drying nitrogen from the low-temperature nitrogen circulation drying unit in the drying tower, and the solvent evaporates to form dry powder particles.

[0043] S4. The dried powder particles are collected by a gas-solid separation device to obtain the product; the moist nitrogen gas is condensed and the solvent is recovered by a solvent recovery condenser, and then returned to the drying tower for recycling after being deeply dehumidified by an adsorption dryer.

[0044] Preferably, the solid content of the liquid in step S1 is 10%~50%, the viscosity is 1~500mPa·s, the surface tension is 30~75mN / m, and the dielectric constant is 40~80.

[0045] The Coulomb electric field strength generated by the electrode ring or conical ring electrode in step S2 is 1×10⁻⁶. 5 ~5×10 6 V / m;

[0046] The temperature of the low-temperature drying nitrogen gas in step S3 is -20℃ to 100℃, preferably 0℃ to 60℃.

[0047] The present invention adopts the above technical solution and has the following technical effects compared with the prior art:

[0048] (1) The electrode ring of the present invention maintains a non-contact gap (≥5mm) between itself and the nozzle outlet. The high-voltage electrode does not have any form of direct or quasi-contact with the liquid material, which fundamentally avoids the problems of electrode contamination, electrochemical reaction and microcapsule structure destruction in the prior art of contact electrostatic spraying. For microcapsule liquid materials containing active core materials (probiotics, enzyme preparations, vaccines, etc.), the shell-core structure is completely maintained, and the encapsulation rate and activity retention rate are significantly improved. Experimental data show that the encapsulation rate of the microcapsule products prepared by the present invention can reach 85%~95%, and the activity retention rate of probiotics can reach 70%~90%, while the activity retention rate of traditional high-temperature spray drying is only 10%~30%.

[0049] (2) This invention cleverly utilizes the differential effect of the Coulomb electric field on polar and non-polar molecules. While the droplets are polarized and dispersed, the polar molecules of the shell material are promoted to be oriented and enriched on the surface of the droplets, and the non-polar molecules of the core material tend to move into the interior of the droplets, spontaneously forming a regular shell-core microcapsule structure with good encapsulation effect. No additional emulsifiers or structure inducers are required, which simplifies the formulation design and production process and reduces production costs.

[0050] (3) The local electric field force generated by the Coulomb field polarization overcomes the surface tension of the liquid, causing the droplets to spontaneously split and disperse further. The resulting polarized mist droplets have smaller particle size (D50 can reach 5~20μm) and more uniform distribution (particle size distribution span value can be less than 1.5), which greatly increases the specific surface area of ​​the droplets and effectively compensates for the problem of insufficient mass and heat transfer driving force under low temperature drying conditions, thus realizing efficient and rapid drying under low temperature conditions.

[0051] (4) The droplets of the present invention obtain polarized charges through dielectric polarization rather than contact conduction. Although there is separation of positive and negative polarized charges on the surface of the droplets, the whole is electrically neutral or close to electrically neutral. This avoids the problem of net charged droplets depositing and sticking to the inner wall of the drying tower due to electrostatic adsorption, which is common in the prior art. This significantly improves the product yield (by 15% to 30%), reduces the frequency of equipment cleaning, and extends the continuous production cycle.

[0052] (5) The present invention can use multi-ring stepped electrodes to realize a gradient Coulomb field, or a conical ring electrode to realize a continuous non-uniform electric field. The diameter, number, spacing, voltage and other parameters of the electrode rings can be flexibly adjusted according to different liquid characteristics (viscosity, surface tension, dielectric constant, conductivity, etc.) and different product requirements, and has a wide range of process adaptability.

[0053] (6) This invention integrates a low-temperature nitrogen circulation drying unit, equipped with solvent recovery condensation and adsorption drying deep dehumidification functions, to realize the whole process closed circulation of the drying medium, which not only saves nitrogen consumption (nitrogen consumption is only 5%~10% of the traditional open circuit system), but also recovers organic solvents, making it safe and environmentally friendly, and particularly suitable for spray drying processes of organic solvent systems.

[0054] (7) An insulating coating (polytetrafluoroethylene or ceramic coating) can be provided on the electrode surface, which not only prevents abnormal discharge arcing, but also ensures the effective penetration of the coulomb electric field, thereby improving the operational safety and stability of the system; at the same time, since the droplets do not carry a net charge, the risk of corona discharge and breakdown discharge in the drying tower is avoided. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the overall process of the droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect of the present invention;

[0056] Figure 2 A schematic diagram of the Coulomb field polarized atomizing nozzle structure configured for a single electrode ring of the present invention;

[0057] Figure 3 A schematic diagram of the Coulomb field polarized atomizing nozzle structure configured with multi-ring stepped electrodes according to the present invention;

[0058] Figure 4 A schematic diagram of the Coulomb field polarized atomizing nozzle structure configured for the conical ring electrode of the present invention;

[0059] The accompanying figures are labeled as follows:

[0060] 100. Liquid supply unit; 101. Liquid storage tank; 102. Feed pump;

[0061] 200. Atomizing nozzle; 201. Liquid inlet pipe; 202. Atomizing gas inlet; 203. Nozzle outlet;

[0062] 300. High-voltage polarized electrode unit; 301. Schematic line of polarized electric field; 302. Polarized droplet; 310. Electrode ring; 310a. First electrode ring; 310b. Second electrode ring; 310c. Third electrode ring; 320. Conical ring electrode;

[0063] 400. Drying tower; 401. Upper interface of drying tower; 402. Low-temperature nitrogen inlet;

[0064] 500. Low-temperature nitrogen circulating drying unit; 501. Nitrogen replenishment port; 502. Nitrogen circulating fan; 503. Nitrogen heater / cooler; 504. Gas-solid separation device; 505. Finished product collection tank; 506. Solvent recovery condenser; 507. Adsorption dryer; 508. Tail gas filter;

[0065] 600, High-voltage power supply;

[0066] d, non-contact gap; d1, first non-contact gap; d2, second non-contact gap; d3, third non-contact gap; d4, non-contact gap of the conical ring electrode; α, cone angle. Detailed Implementation

[0067] like Figure 1 As shown, the droplet polarization atomization low-temperature spray drying system based on Coulomb field effect provided by the present invention mainly includes: a liquid supply unit 100, an atomizing nozzle 200, a high-voltage polarization electrode unit 300, a high-voltage power supply 600, a drying tower 400, and a low-temperature nitrogen circulation drying unit 500.

[0068] The core working principle of this invention is as follows: After the liquid is initially atomized by the atomizing nozzle 200, it forms initial droplets. These droplets move downwards under gravity, passing through the Coulomb electric field region generated by the high-voltage polarized electrode unit 300. Under the influence of the Coulomb electric field, polar molecules inside the droplets (such as water molecules and organic molecules containing polar groups) undergo dielectric polarization, inducing a separation distribution of positive and negative polarized charges on the droplet surface. The local electric field force generated by the polarized charges interacts with the surface tension of the liquid. When the electric field force exceeds the surface tension, the droplets further split and disperse, forming a cluster of smaller, more uniformly distributed polarized droplets. Simultaneously, for the microcapsule liquid system containing a shell and a core material, the Coulomb field polarization promotes the polar molecules of the shell material to oriented and enrich towards the droplet surface, while the non-polar molecules of the core material tend to move towards the interior of the droplet, thus spontaneously forming a shell-core microcapsule structure.

[0069] Because a non-contact gap is maintained between the high-voltage polarized electrode unit 300 and the outlet of the atomizing nozzle 200, the electrode does not directly contact the feed liquid, thus avoiding problems such as electrode contamination, electrochemical reactions, and microcapsule structure damage caused by contact charging. The droplets acquire polarization charge only through coulombic field dielectric polarization, rather than through contact conduction. Therefore, the droplets are generally electrically neutral or nearly electrically neutral, avoiding electrostatic adsorption and deposition of charged droplets on the drying tower wall, and improving product yield.

[0070] The low-temperature nitrogen circulation drying unit 500 provides a low-temperature drying environment (typically -20℃ to 100℃), which, combined with the high specific surface area droplet clusters (D50 up to 5~20μm) generated by polarized atomization, enables rapid and efficient drying at lower temperatures, making it particularly suitable for the preparation of heat-sensitive materials and microcapsule products.

[0071] The present invention will now be described in detail and specifically through specific embodiments to enable a better understanding of the invention. However, the following embodiments do not limit the scope of the invention.

[0072] Example 1: Low-temperature spray drying system and method with single-ring electrode configuration

[0073] like Figure 1 and Figure 2 As shown, this embodiment provides a droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect, including a liquid supply unit 100, an atomizing nozzle 200, a high-voltage polarization electrode unit 300, a high-voltage power supply 600, a drying tower 400, and a low-temperature nitrogen circulation drying unit 500.

[0074] The liquid supply unit 100 includes a liquid storage tank 101 and a feed pump 102. The liquid storage tank 101 is a sealed stainless steel container with a volume of 50L to 1000L, selectable according to production scale. The liquid storage tank 101 is equipped with a stirring device (not shown in the figure) to maintain the uniformity and stability of the liquid and prevent solid sedimentation. The feed pump 102 is a precision metering pump, selected from peristaltic pumps, gear pumps, or diaphragm pumps, used to deliver the liquid to be dried to the atomizing nozzle 200 at a controllable flow rate. The flow rate of the feed pump 102 is 10mL / min to 2000mL / min, with a control accuracy of ±2%. The liquid storage tank 101 and the feed pump 102 are connected by a stainless steel pipe equipped with a filter (not shown in the figure) to remove large particulate impurities from the liquid and prevent nozzle clogging.

[0075] In this embodiment, the liquid to be dried is an aqueous dispersion containing shell material and core material, with a solid content of 10%~50%. The shell material is selected from one or more combinations of maltodextrin, gum arabic, modified starch, β-cyclodextrin, sodium alginate, and chitosan, and is used to form the protective outer shell of the microcapsules; the core material is selected from one or more of probiotics (such as Bifidobacterium lactis, Lactobacillus acidophilus, Lactobacillus plantarum, etc.), vitamins (such as vitamin A, vitamin E, vitamin C, etc.), and essential oils (such as lemon oil, peppermint oil, rose oil, etc.). The viscosity of the liquid is 1~500 mPa·s (25℃), the surface tension is 30~75 mN / m, and the dielectric constant is 40~80.

[0076] The atomizing nozzle 200 is a dual-fluid airflow atomizing nozzle, including a liquid inlet pipe 201, an atomizing gas inlet 202, and a nozzle outlet 203. The inner diameter of the liquid inlet pipe 201 is 1mm to 10mm, and it is connected to the outlet pipe of the feed pump 102. The atomizing gas inlet 202 is located on the side wall or top of the nozzle 200 and is connected to a compressed nitrogen gas source. The nozzle outlet 203 is arranged downwards, and the outlet orifice diameter is 0.5mm to 5mm. After the liquid is mixed with the high-speed atomizing gas inside the nozzle 200, it is sprayed downwards from the nozzle outlet 203 to form initial droplets. The atomizing gas is compressed nitrogen, with a pressure of 0.1MPa to 1.0MPa, preferably 0.2MPa to 0.6MPa. The flow rate of the atomizing gas is precisely controlled by a mass flow meter (not shown in the figure), and the gas-liquid mass ratio is 0.5:1 to 5:1, preferably 1:1 to 3:1. The temperature of the atomizing gas can be pre-adjusted to be the same as or close to the drying temperature to avoid large temperature differences that could lead to instability in the atomization process.

[0077] As an alternative, the atomizing nozzle 200 can also be any of a pressure nozzle, centrifugal nozzle, or ultrasonic nozzle, as long as it can generate initial droplets. Pressure nozzles are suitable for low-viscosity liquids, where the liquid is pressurized to 2MPa~20MPa by a high-pressure pump and then sprayed out of the nozzle to achieve atomization; centrifugal nozzles are suitable for high-volume processing conditions, where the liquid is flung out by a high-speed rotating (5000~50000rpm) atomizing disc to achieve atomization; ultrasonic nozzles are suitable for applications with extremely low flow rates and high precision requirements, where ultrasonic vibration breaks the liquid into fine droplets.

[0078] The high-voltage polarization electrode unit 300 includes an electrode ring 310. The electrode ring 310 is made of a conductive metal material; in this embodiment, 304 stainless steel is used, and the ring has a circular cross-section. The inner diameter of the electrode ring 310 is 20mm to 200mm, determined according to the nozzle outlet diameter and spray cone angle, typically 2 to 10 times the nozzle outlet diameter. The electrode ring 310 is coaxially arranged directly below the nozzle outlet 200, with its central axis coinciding with the central axis of the nozzle outlet 203. The plane containing the electrode ring 310 is parallel to the horizontal plane. The non-contact gap d between the upper end face of the electrode ring 310 and the lower end face of the nozzle outlet 203 is 10mm to 50mm, preferably 20mm in this embodiment.

[0079] The surface of the electrode ring 310 may be provided with an insulating coating, which may be a polytetrafluoroethylene coating or a ceramic coating, with a coating thickness of 0.05 mm to 2 mm, preferably 0.2 mm to 0.8 mm. The insulating coating serves several purposes: preventing abnormal discharge and arcing of the high-voltage electrode under humid or high electric field conditions; preventing contamination and corrosion of the electrode surface by liquid splashes; and improving system operational safety while ensuring effective penetration of the coulombic electric field. The insulating coating does not affect the spatial distribution of the electric field, as the polarization electric field mainly depends on the electrode geometry and the applied voltage; the insulating layer only provides electrical isolation and protection.

[0080] The high-voltage power supply 600 is an adjustable high-voltage DC power supply. Its positive or negative terminal is electrically connected to the electrode ring 310, and the other terminal is grounded. The output voltage range of the high-voltage power supply 600 is ±5kV to ±100kV, preferably ±10kV to ±60kV, more preferably ±20kV to ±50kV, with an output power of 50W to 500W and a voltage ripple coefficient of less than 0.1%. In this embodiment, the high-voltage power supply 600 applies a negative high-voltage DC current of -30kV to the electrode ring 310, making the electrode ring 310 negatively potential relative to the ground terminal. The high-voltage power supply 600 is equipped with overcurrent protection, overvoltage protection, and short-circuit protection functions. When the discharge current exceeds a set threshold (e.g., 1mA), the output is automatically cut off to ensure system safety. The output voltage of the high-voltage power supply 600 can be adjusted according to parameters such as the conductivity, dielectric constant, and surface tension of the liquid to achieve the best polarization and dispersion effect.

[0081] The drying tower 400 has a cylindrical-conical bottom structure. The tower body is made of stainless steel, and the inner wall is polished to a surface roughness Ra≤0.8μm to reduce powder adhesion to the wall. The diameter and height of the drying tower 400 are determined according to the throughput. In this embodiment, the diameter of the drying tower is 800mm~3000mm, and the height is 2000mm~8000mm. A nozzle mounting interface 401 is provided at the top of the drying tower 400 for fixing and installing the atomizing nozzle 200. The nozzle outlet 203 extends into the interior of the drying tower 400 by a certain distance (50mm~300mm). Low-temperature nitrogen inlet 402 and nitrogen outlet (not shown in the figure) are respectively provided on the upper and lower (or conical bottom) side walls of the drying tower 400 for introducing and discharging the drying medium. A discharge port is provided at the bottom of the drying tower 400, which is connected to the gas-solid separation device 504.

[0082] The low-temperature nitrogen circulating drying unit 500 is connected to the drying tower 400 and is used to supply low-temperature dry nitrogen to the drying tower 400 for recycling. The low-temperature nitrogen circulating drying unit 500 includes: a nitrogen heater / cooler 503, a nitrogen circulating fan 502, a gas-solid separation device 504, a finished product collection tank 505, a solvent recovery condenser 506, an adsorption dryer 507, a tail gas filter 508, and a nitrogen replenishment port 501.

[0083] The nitrogen heater / cooler 503 employs a shell-and-tube heat exchanger or a plate heat exchanger, indirectly exchanging heat with the circulating nitrogen through heat exchange media such as circulating hot water, steam, chilled water, or chilled ethylene glycol to regulate the circulating nitrogen to the target drying temperature. In this embodiment, the target drying temperature is 25℃~40℃. When a higher temperature is required, it can be heated by hot water or steam; when a lower temperature is required (such as below zero), it can be cooled by chilled ethylene glycol or liquid nitrogen. The heat exchange area of ​​the nitrogen heater / cooler 503 is determined according to the processing capacity to ensure that the nitrogen temperature control accuracy is ±2℃.

[0084] The nitrogen circulation fan 502 is a centrifugal fan or a Roots blower used to drive the circulation of nitrogen within the system. The flow rate of fan 502 is 100~10000 m³ / h, the total pressure is 2~20 kPa, the material is stainless steel, and the sealing method is a mechanical seal or magnetic seal to ensure no nitrogen leakage.

[0085] The gas-solid separation device 504 is used to separate the dried powder particles from nitrogen gas. In this embodiment, the gas-solid separation device 504 is a cyclone separator with a separation efficiency of 90%~99% and a particle size d50 of 2~10μm. Alternatively, the gas-solid separation device 504 can also be any one or a combination of bag filters, sintered metal filters, or electrostatic precipitators. The separated powder particles are stored in the finished product collection tank 505. The finished product collection tank 505 is a sealed stainless steel container with a volume of 10L~500L and is equipped with a discharge valve.

[0086] The solvent recovery condenser 506 is used to condense and recover evaporated solvents (such as water vapor, organic solvent vapors, etc.) carried in nitrogen. In this embodiment, the solvent is water. The condenser 506 uses chilled water (7℃~12℃) or chilled ethylene glycol (-5℃~5℃) as the cooling medium to cool the nitrogen to 5℃~15℃, causing the water vapor to condense into liquid water before being discharged. For organic solvent systems, the condensation temperature needs to be set according to the boiling point and saturated vapor pressure curve of different solvents (e.g., -10℃~0℃ for ethanol system, -20℃~-10℃ for acetone system). The solvent recovery condenser 506 adopts a shell-and-tube or plate structure, and the heat exchange area is determined according to the processing capacity.

[0087] The adsorption dryer 507 is used for deep dehumidification of condensed nitrogen gas to lower its dew point temperature. The adsorption dryer 507 contains molecular sieves (such as 3A, 4A, 5A, or 13X molecular sieves) or silica gel adsorbent to adsorb residual moisture in the nitrogen gas to below the dew point of -40°C. The adsorption dryer 507 employs a conventional dual-tower alternating regeneration design (one tower for online drying and adsorption, and the other for offline heating and regeneration), enabling continuous and uninterrupted operation. Regeneration is performed via heating at temperatures ranging from 150°C to 300°C for 2 to 8 hours, using a small amount of dry nitrogen or compressed air for regeneration.

[0088] The exhaust gas filter 508 is installed at the system's exhaust port to filter trace amounts of dust in the nitrogen gas during overpressure discharge, preventing environmental pollution. The exhaust gas filter 508 has a filtration accuracy of 0.1~5μm and is made of PTFE membrane filter media or sintered stainless steel filter element.

[0089] The nitrogen replenishment port 501 is connected via pipes to the atomizing gas inlet 202 of the atomizing nozzle 200 and the inlet side of the nitrogen circulating fan 502, respectively, to replenish the nitrogen lost due to minor leaks in the system and maintain a constant nitrogen pressure (slight positive pressure, such as 0.1~0.5 kPa) in the system. A pressure reducing valve, a flow meter, and a check valve are installed at the nitrogen replenishment port 501.

[0090] The droplet polarization atomization low-temperature spray drying method based on the Coulomb field effect in this embodiment includes the following steps:

[0091] S1. Feed Delivery and Initial Atomization: The prepared feed solution to be dried is added to the feed storage tank 101, and the stirring device is turned on to keep the feed solution uniform. The feed pump 102 is started, and the feed solution is delivered to the atomizing nozzle 200 through the feed inlet pipe 201 at a flow rate of 50~500mL / min (determined according to the processing capacity; 200mL / min in this embodiment). At the same time, compressed nitrogen gas is introduced into the atomizing nozzle 200 through the atomizing gas inlet 202. The atomizing gas pressure is 0.2MPa~0.6MPa (0.4MPa in this embodiment), and the gas-liquid mass ratio is 1.5:1. After the feed solution and high-speed atomizing gas are mixed inside the nozzle 200, they are sprayed downward from the nozzle outlet 203 to form initial droplets. The average particle size D50 of the initial droplets is 50~150μm, depending on the physical properties of the feed solution, the atomizing gas pressure, and the flow rate.

[0092] S2. Coulomb Field Polarization Dispersion: The initial droplets move downwards at a speed of approximately 1~5 m / s under the influence of gravity, passing through the central hole region of the electrode ring 310. A high-voltage direct current of -30 kV is applied to the electrode ring 310 by a high-voltage power supply 600, forming a strong Coulomb electric field (with an electric field strength of approximately 1 × 10⁻⁶) around the electrode ring 310. 5 ~5×10 6 V / m). When the initial droplet enters the Coulomb electric field region, the polar molecules inside the droplet (such as water molecules and polar groups in the shell) are dielectrically polarized under the action of the electric field, and the centers of positive and negative charges are relatively displaced, inducing a separation distribution of positive and negative polarized charges on the surface of the droplet (the side closer to the electrode ring induces a charge of the opposite sign to the electrode, and the side farther from the electrode ring induces a charge of the same sign as the electrode).

[0093] The local electric field force generated by the polarization charge on the droplet surface is opposite to the direction of the liquid surface tension. When the polarization electric field force overcomes the liquid surface tension, the droplet deforms and further splits into smaller droplets. Simultaneously, for microcapsule solutions containing shell and core materials, the polar molecules of the shell material (such as the polar groups in maltodextrin and gum arabic) are oriented and enriched towards the droplet surface under the influence of the Coulomb electric field, while the non-polar molecules of the core material (such as oils and essential oils) tend to move into the droplet interior, thus spontaneously forming a shell-core microcapsule structure. After Coulomb field polarization dispersion, the average droplet size decreases from the initial 50~150 μm to D50 = 10~25 μm, resulting in a more uniform droplet size distribution.

[0094] S3. Low-Temperature Drying: The polarized droplet cluster 302 continues to move downwards into the main drying area of ​​the drying tower 400. The nitrogen heater / cooler 503 in the low-temperature nitrogen circulating drying unit 500 adjusts the circulating nitrogen to 25℃~40℃, and introduces it into the drying tower 400 through the low-temperature nitrogen inlet 402 in a parallel or counter-current flow with the droplet movement direction. After the polarized droplet cluster 302 comes into contact with the low-temperature drying nitrogen, the moisture evaporates rapidly, forming dried powder particles. Due to the significantly reduced particle size of the polarized droplets and the substantial increase in specific surface area (5~20 times greater than the initial droplets), rapid mass and heat transfer can be achieved even under low-temperature conditions (25℃~40℃), shortening the drying time to 1~10 seconds.

[0095] S4. Product Collection and Nitrogen Circulation: The dried powder particles are carried by the nitrogen gas flow into the gas-solid separation device 504 (cyclone separator). Under centrifugal force, the powder particles are separated and fall into the finished product collection tank 505, yielding the microcapsule product. The humid nitrogen gas (relative humidity 60%~90%) discharged from the gas-solid separation device 504 enters the solvent recovery condenser 506, where it is cooled to 5℃~15℃, and most of the water vapor is condensed into liquid water before being discharged. The condensed nitrogen gas then enters the adsorption dryer 507, where it is deeply dehumidified to below -40℃ using molecular sieves or silica gel adsorbents. The dried nitrogen gas is then sent back to the nitrogen heater / cooler 503 by the nitrogen circulation fan 502 to be heated to the target temperature before re-entering the drying tower 400, completing the closed-loop circulation.

[0096] The microcapsule product prepared in this embodiment is a spherical or near-spherical powder particle with an average particle size D50 of 15-30 μm. The product has a moisture content of less than 5% and good flowability. The encapsulation efficiency of the microcapsules can reach 85%-95%, and the core material retention rate can reach 80%-95%. For probiotic microcapsule products, the probiotic activity retention rate can reach 70%-90% (based on the initial viable count), and the activity retention rate can still be maintained at more than 60% of the initial value after being stored at 4°C for 6 months. The product yield can reach 90%-98%, and the amount of residue adhering to the tower wall is reduced by 60%-80% compared with traditional electrostatic spraying technology, significantly reducing the frequency of equipment cleaning.

[0097] Example 2: Low-temperature spray drying system and method with multi-ring stepped electrode configuration

[0098] like Figure 3 As shown, the basic system structure of this embodiment is the same as that of embodiment 1. The difference is that the high-voltage polarization electrode unit 300 uses a multi-ring stepped electrode group instead of the single electrode ring in embodiment 1.

[0099] Specifically, the multi-ring stepped electrode assembly includes three electrode rings arranged vertically from top to bottom at intervals: a first electrode ring 310a, a second electrode ring 310b, and a third electrode ring 310c. All three electrode rings are made of conductive metal (304 stainless steel), have a circular cross-section, and a diameter of 2mm to 6mm. The inner diameters of the three electrode rings increase sequentially from top to bottom, being 30mm, 50mm, and 80mm respectively, to accommodate the actual situation where the spray cone angle gradually expands as the droplets move downwards.

[0100] The first non-contact gap d1 between the upper end face of the first electrode ring 310a and the lower end face of the nozzle outlet 203 is 15 mm. The second non-contact gap d2 between the first electrode ring 310a and the second electrode ring 310b is 20 mm. The third non-contact gap d3 between the second electrode ring 310b and the third electrode ring 310c is 30 mm. The spacing between adjacent electrode rings can be optimized according to the needs of electric field distribution and the characteristics of droplet polarization process. The spacing between adjacent electrode rings is 5 mm to 80 mm, preferably 15 mm to 40 mm.

[0101] Each electrode ring is powered by the same high-voltage power supply 600, or it can be powered by an independent high-voltage power supply for independent adjustment. In this embodiment, all three electrode rings are powered by the same high-voltage power supply 600, with a voltage of -40kV applied to each. Alternatively, each electrode ring can be powered by its own independently adjustable high-voltage power supply, and the voltage difference between adjacent electrode rings can be set independently to form the desired gradient Coulomb field. For example, the first electrode ring 310a is applied with -20kV, the second electrode ring 310b with -40kV, and the third electrode ring 310c with -60kV, forming a progressively increasing Coulomb field gradient.

[0102] Due to the different diameters and positions of the electrode rings, a gradient-distributed Coulomb electric field 301 is formed in the space below the nozzle. As the droplet passes through the three electrode rings sequentially, it undergoes progressively increasing polarization. The droplet first passes through the electric field region of the first electrode ring 310a, undergoing primary polarization dispersion; then it passes through the electric field region of the second electrode ring 310b, undergoing further polarization dispersion under the influence of a stronger electric field; finally, it passes through the electric field region of the third electrode ring 310c, completing full polarization dispersion. The average particle size D50 can reach 5~15 μm, and the particle size distribution span (Span) can be less than 1.5.

[0103] The gradient electric field configuration of multi-ring stepped electrodes is particularly suitable for liquid systems with high viscosity (>100 mPa·s) and high surface tension (>50 mN / m). This is because high-viscosity liquids have strong cohesion, and single polarization is not enough to achieve sufficient dispersion. It is necessary to overcome the cohesion of droplets step by step by gradually increasing the polarization force to achieve sufficient dispersion.

[0104] As an extension of this embodiment, the number of electrode rings in the multi-ring stepped electrode group is not limited to three; it can be set to two, four, or more (e.g., 2 to 10) as needed to form a multi-level polarized electrode group. A larger number of electrode rings allows for more precise electric field gradient control, but it increases equipment cost and structural complexity. The diameter of the electrode rings is not limited to increasing sequentially from top to bottom; it can also decrease sequentially from top to bottom to adapt to the conditions of contraction-type spray shapes.

[0105] The working method of this embodiment is basically the same as that of embodiment 1. The difference is that in step S2, the initial droplet passes through the gradient Coulomb electric field region generated by the first electrode ring 310a, the second electrode ring 310b and the third electrode ring 310c in sequence, and undergoes a progressively enhanced polarization effect.

[0106] Specifically, the feed pump 102 delivers the liquid feed to the atomizing nozzle 200 at a flow rate of 200 mL / min. After mixing with compressed nitrogen gas at 0.4 MPa, the liquid is ejected from the nozzle outlet 203 to form initial droplets (D50≈80 μm). The initial droplets first pass through the electric field region of the first electrode ring 310a (applied -40 kV), where they undergo primary polarization dispersion under the action of the Coulomb field, reducing the average droplet size to approximately 40 μm. Subsequently, the droplets pass through the electric field region of the second electrode ring 310b (applied -40 kV) for further polarization dispersion, reducing the average droplet size to approximately 25 μm. Finally, the droplets pass through the electric field region of the third electrode ring 310c (applied -40 kV), completing the final polarization dispersion, reducing the average droplet size to approximately 10 μm. After undergoing three-stage gradient polarization dispersion, the droplet group enters the main area of ​​the drying tower 400, where it comes into contact with low-temperature nitrogen gas at 20℃~35℃ to complete the drying process.

[0107] Due to the stepwise effect of the gradient electric field, the dispersion process of the droplets is more stable and controllable, avoiding the problems of excessive breakage or uneven dispersion that may occur under a single strong electric field. This is particularly beneficial for obtaining powder products with narrow particle size distribution.

[0108] The microcapsule products prepared in this embodiment have an average particle size D50 of 8~15 μm, a particle size distribution span of less than 1.5, and good product uniformity. For high-viscosity liquids (such as the chitosan-gum arabic composite system with a viscosity of about 200 mPa·s), the encapsulation efficiency in this embodiment can reach 88%~96%, which is about 5~10 percentage points higher than the single-ring electrode configuration in Example 1. This indicates that the gradient polarization effect of the multi-ring stepped electrode has a significant promoting effect on the formation of microcapsules in high-viscosity liquids.

[0109] Example 3: Low-temperature spray drying system and method with conical ring electrode configuration

[0110] like Figure 4 As shown, this embodiment has the same basic system structure as embodiment 1, except that the high-voltage polarization electrode unit 300 uses a conical ring electrode 320 instead of the single ring electrode in embodiment 1.

[0111] The conical ring electrode 320 is a truncated conical metal ring with an inner diameter that gradually increases from top to bottom. It is made of conductive metal material (316L stainless steel) and has a wall thickness of 1mm to 5mm. The upper inner diameter of the conical ring electrode 320 is 20mm to 60mm (30mm in this embodiment), the lower inner diameter is 60mm to 200mm (90mm in this embodiment), and the axial height is 20mm to 150mm (60mm in this embodiment). The cone angle α of the conical ring electrode 320 is 5° to 60°, preferably 10° to 45°, and is 30° in this embodiment. The non-contact gap d4 between the upper end face of the conical ring electrode 320 and the lower end face of the nozzle outlet 203 is 5mm to 50mm, and is 15mm in this embodiment.

[0112] The inner wall of the conical ring electrode 320 is a smooth conical surface with a surface roughness Ra≤1.6μm, and an insulating coating (polytetrafluoroethylene or ceramic coating, thickness 0.1mm~1mm) can be applied. The conical ring electrode 320 is electrically connected to the high-voltage power supply 600 via a high-voltage wire.

[0113] A high-voltage power supply 600 applies a -45kV high-voltage direct current to the conical ring electrode 320. Due to the conical inner wall shape of the conical ring electrode 320, a continuous non-uniform Coulomb electric field is generated in both the axial and radial directions. The electric field strength is strongest near the inner wall of the conical ring electrode 320, gradually weakens radially inward, and exhibits a continuous variation along the axial direction from top to bottom due to the expansion of the conical inner diameter. As the droplet passes through the internal space of the conical ring electrode 320, it undergoes a continuous evolution from primary polarization to full polarization in the continuously changing electric field, resulting in a smooth and uniform dispersion effect.

[0114] As an alternative, the cone angle of the conical ring electrode 320 can be a positive cone (smaller at the top and larger at the bottom, as in this embodiment) or an inverted cone (larger at the top and smaller at the bottom), which can be selected according to the spray cone angle and the characteristics of the liquid. The conical ring electrode 320 has a simple structure, requiring only one electrode element to achieve the gradient electric field effect, and is easy to manufacture, install, and clean and maintain.

[0115] The working method of this embodiment is basically the same as that of embodiment 1, except that in step S2, the initial droplet passes through the continuous non-uniform coulomb electric field region generated by the conical ring electrode 320.

[0116] The feed pump 102 delivers the liquid feed to the atomizing nozzle 200 at a flow rate of 200 mL / min. After mixing with compressed nitrogen gas at 0.4 MPa, the mixture is ejected from the nozzle outlet 203 to form initial droplets (D50 ≈ 80 μm). After entering the internal space of the conical ring electrode 320, the electric field intensity experienced by the initial droplets changes continuously as they move downwards: in the upper region of the conical ring electrode 320 (electric field intensity approximately 2 × 10⁻⁶), the electric field intensity changes accordingly. 5 With an electric field strength of V / m, the droplet undergoes primary polarization and its size decreases slightly; as the droplet moves towards the lower region of the conical ring electrode 320 (the electric field strength gradually increases to approximately 1×10), the droplet undergoes primary polarization and its size decreases slightly; 6 (V / m), the polarization effect gradually increases, and the droplet continuously splits into smaller droplets; when the droplet moves to the vicinity of the lower end outlet of the conical ring electrode 320, the polarization dispersion reaches the most sufficient state, and the average particle size drops to about 8μm.

[0117] Because the electric field is continuously changing, the droplet dispersion process is smooth and uniform, avoiding the droplet instability caused by sudden changes in the electric field that may occur in a stepped electric field. The average particle size D50 of the droplet group after dispersion by the conical ring electrode 320 is 8~20μm, and the particle size distribution span value is less than 1.3.

[0118] The microcapsule product prepared in this embodiment has an average particle size D50 of 10~20μm, a very concentrated particle size distribution (Span value less than 1.3), and good product appearance uniformity. For medium viscosity (50~150mPa·s) liquids, the encapsulation efficiency of this embodiment can reach 88%~95%, which is comparable to the multi-ring stepped electrode configuration of Example 2, but the electrode structure is simpler and the cost is lower. The conical ring electrode 320 has no sharp edges, is not easy to accumulate material and contaminate, is easy to clean and maintain, and is more suitable for industrial continuous production.

[0119] Example 4: Optimization Experiment of Microcapsule Encapsulation Process

[0120] (1) System structure and process parameters

[0121] This embodiment uses the same system structure (single-ring electrode configuration) as in Embodiment 1, but it has been specifically optimized for the microcapsule encapsulation process, focusing on the microcapsule formation effect under different voltage parameters and feed formulations.

[0122] The emulsion formulation is as follows: The shell material is a compound system of maltodextrin (DE value 15~20) and gum arabic, with a total solids content of 25% (mass fraction), wherein the mass ratio of maltodextrin to gum arabic is 2:1. The core material is vitamin E acetate, with a core material to shell material mass ratio of 1:4. A small amount of emulsifier (glyceryl monostearate, added at 0.5% of total solids) is added to the emulsion to assist in emulsification and stabilization. The emulsion is heated and stirred at 60℃ for 30 minutes to completely dissolve the shell material and uniformly disperse the core material, forming an oil-in-water emulsion. The viscosity of the emulsion is 80 mPa·s (60℃), the surface tension is 42 mN / m, and the dielectric constant is 65.

[0123] Process parameters: feed flow rate 150mL / min, atomizing gas pressure 0.5MPa, gas-liquid mass ratio 2:1, drying tower inlet temperature 30℃, outlet temperature 18℃, nitrogen circulation flow rate 800m³ / h, electrode ring inner diameter 50mm, non-contact gap 20mm.

[0124] (2) Experimental Design and Results

[0125] To investigate the effect of voltage on microcapsule encapsulation efficiency, six voltage gradients were set up in this embodiment: 0 kV (control group, no high voltage applied), -10 kV, -20 kV, -30 kV, -40 kV, and -50 kV. Each condition was run for 30 minutes, and the product was collected to determine the microcapsule encapsulation efficiency, particle size distribution, and vitamin E retention rate. The experimental results are shown in Table 1 below.

[0126] Table 1. Experimental data on the effect of different voltages on microcapsule encapsulation efficiency:

[0127] 0 32.5 72.3 81.5 2.8 -10 25.8 78.6 85.2 2.1 -20 18.2 86.4 90.7 1.3 -30 14.5 92.1 94.3 0.7 -40 12.8 93.5 93.8 0.6 -50 11.2 93.8 92.1 0.6

[0128] As shown in Table 1, the average particle size of the product decreased significantly after applying a Coulombic field voltage (from 32.5 μm to 11.2 μm), indicating that Coulombic field polarization effectively promoted the secondary dispersion of droplets. The encapsulation efficiency increased from 72.3% to 93.8% with increasing voltage, indicating that Coulombic field polarization promoted the formation of the shell-core structure. Vitamin E retention initially increased and then decreased slightly, reaching its optimal value (approximately 94%) at -30 kV and -40 kV, while decreasing slightly at -50 kV (92.1%). This may be due to the trace free radical oxidation of vitamin E caused by the excessively high electric field strength. The surface free oil content decreased from 2.8% to 0.6%, indicating that Coulombic field polarization significantly improved the surface structure of the microcapsules, allowing the core material to be more completely encapsulated within the shell material.

[0129] Based on the above test results and analysis, it can be concluded that the optimal voltage for the vitamin E microcapsule liquid system in this embodiment is -30kV to -40kV. Under this condition, high-quality microcapsule products with an encapsulation rate of >92%, a core material retention rate of >93%, and a surface free oil content of <0.8% can be obtained.

[0130] Example 5: Suitability Experiments for Different Material Systems

[0131] (1) Probiotic microcapsule system

[0132] Formula for the feed solution: 1×10¹ lyophilized Bifidobacterium lactis BB-12 bacterial powder was added. 0 The bacterial suspension was suspended in a protective agent solution containing 10% skim milk powder, 5% trehalose, 1% monosodium glutamate, and 5% maltodextrin. The bacterial suspension was then mixed with a shell material solution (10% gum arabic + 10% modified starch) at a 1:1 mass ratio to form a water-in-water microcapsule solution with a total solids content of approximately 20%.

[0133] System configuration: The system employs the multi-ring stepped electrode configuration of Example 2 (three electrode rings with inner diameters of 30mm, 50mm, and 80mm, all with a voltage of -35kV), with non-contact gaps d1=15mm, d2=20mm, and d3=30mm. The drying tower inlet temperature is 35℃, the outlet temperature is 22℃, the feed flow rate is 100mL / min, and the atomizing gas pressure is 0.3MPa.

[0134] Product performance: The product is a white to pale yellow powder with a moisture content of 3.2%, an average particle size of D50 of 16.8 μm, and a Span of 1.45. The initial viable count of probiotics is 1.0 × 10¹. 0 The CFU / g (based on the product) count after drying is 8.2 × 10⁻⁶. 9CFU / g, activity retention rate 82%. After storage at 4℃ for 3 months, the viable count was 6.5 × 10⁻⁶. 9 The CFU / g retention rate is 65% of the initial value. Compared with traditional high-temperature spray drying (inlet air temperature 160°C) (activity retention rate of about 15%), the method of this invention increases the probiotic activity retention rate by about 5.5 times, which is a significant advantage.

[0135] (2) Protein (whey protein) system

[0136] Feed solution formulation: Whey protein concentrate (WPC80) is dissolved in deionized water at a concentration of 15% (mass fraction), and the pH is adjusted to 6.8. This feed solution does not contain core material and is a single-component system, used to investigate the applicability of the drying method of this invention to drying non-microencapsulated materials.

[0137] System configuration: The conical ring electrode configuration of Example 3 is adopted (cone angle 25°, voltage -25kV), with a non-contact gap of 15mm. The inlet air temperature of the drying tower is 50℃, the outlet air temperature is 35℃, the feed flow rate is 250mL / min, and the atomizing gas pressure is 0.5MPa.

[0138] Product performance: The product is a white powder with a moisture content of 4.5%, an average particle size of D50 of 22.3 μm, and a Span of 1.52. The protein nitrogen solubility index (NSI) is 92.3%, indicating that the protein denaturation is very low and it still maintains good solubility. The product yield is 94.5%, and the amount adhering to the column wall is extremely small.

[0139] (3) Organic solvent (ethanol) system

[0140] Solution formulation: Curcumin (1%) and polyvinylpyrrolidone (PVP K30) (10%) are dissolved in anhydrous ethanol to form an organic solvent solution. This system is flammable and explosive, and requires drying under nitrogen protection.

[0141] System configuration: The system employs the single-ring electrode configuration of Example 1 (60mm inner diameter, -20kV voltage), with a non-contact gap of 25mm. The solvent recovery condenser 506 in the low-temperature nitrogen circulating drying unit 500 is set to -5℃ to 0℃ (the condensation temperature of ethanol), and the adsorption dryer 507 is filled with hydrophobic molecular sieves. The inlet temperature of the drying tower is 60℃, the outlet temperature is 35℃, the feed flow rate is 80mL / min (the ethanol system requires a lower feed rate due to flash point limitations), and the atomizing gas pressure is 0.2MPa.

[0142] Product performance: The product is an orange-yellow powder with a curcumin content of 9.8% (close to the theoretical value of 10%), an average particle size of D50 of 18.5 μm, and a span of 1.38. The residual ethanol content is <0.5% (meeting the limits of the Chinese Pharmacopoeia), and the product yield is 92.8%. The ethanol recovered by the solvent recovery condenser 506 has a purity of 98.5% and can be recycled.

[0143] The above three examples of different material systems demonstrate that the drying system and method of the present invention have good versatility and flexibility. By adjusting process conditions such as electrode configuration, voltage parameters and drying temperature, it can be applied to low-temperature spray drying of water systems, organic solvent systems and different heat-sensitive materials (probiotics, proteins, natural active ingredients, etc.).

[0144] Example 6: Comparative Experiment with Different Electrode Parameters

[0145] (1) Experimental objective

[0146] This embodiment examines the effects of electrode ring inner diameter, non-contact gap d, and applied voltage on polarization atomization effect and product performance through systematic comparative experiments, providing data support for actual process optimization.

[0147] (2) Experimental design

[0148] The single-ring electrode configuration system of Example 1 was used, with the feed solution fixed as a maltodextrin aqueous solution (20% solid content), a feed flow rate of 200 mL / min, an atomizing gas pressure of 0.4 MPa, and a drying temperature of 30°C. The following parameters were varied:

[0149] (1) Inner diameter of electrode ring: 20mm, 40mm, 60mm, 80mm, 120mm (fixed voltage -30kV, gap 20mm);

[0150] (2) Non-contact gap d: 5mm, 15mm, 25mm, 40mm, 60mm, 100mm (fixed voltage -30kV, inner diameter 60mm);

[0151] (3) Applied voltage: 0kV, -10kV, -20kV, -30kV, -40kV, -50kV, -60kV (fixed inner diameter 60mm, gap 20mm).

[0152] Each condition was repeated three times to determine the average particle size D50, particle size distribution Span value, and product yield.

[0153] (3) Experimental results

[0154] Table 2. Influence data of different electrode ring inner diameters:

[0155] Inner diameter (mm) D50(μm) Span value Product yield (%) Observing phenomena 20 12.8 1.45 92.5 Droplets at the edge of the spray cone are prone to touching the electrodes. 40 13.5 1.38 94.2 Good polarization effect 60 14.2 1.35 95.8 Optimal polarization effect 80 16.8 1.48 96.0 The electric field strength in the central region is low. 120 24.5 1.72 95.5 The polarization effect is significantly weakened.

[0156] As shown in Table 2 above, the inner diameter of the electrode ring has a significant impact on the polarization effect. When the inner diameter is too small (20 mm), droplets at the edge of the spray cone easily touch the electrode, leading to droplet deposition on the electrode surface and possible discharge. When the inner diameter is too large (120 mm), the electrode ring is far from the main body of the spray cone, and the electric field strength in the central area is insufficient to effectively polarize all droplets. The optimal inner diameter is 40-80 mm (approximately 4-8 times the nozzle outlet diameter), at which point the polarization effect is optimal and the product yield is highest.

[0157] Table 3. Influence data of non-contact gap d

[0158] 5 11.8 1.52 88.5 The electric field is too concentrated, and occasional discharges occur. 15 13.2 1.38 94.8 Excellent polarization effect 25 14.5 1.36 96.0 Good polarization effect 40 17.2 1.45 96.5 Medium polarization effect 60 22.8 1.62 96.8 The polarization effect is relatively weak. 100 30.5 1.78 96.5 weak polarization effect

[0159] As shown in Table 3 above, the non-contact gap d also significantly affects the polarization effect. When the gap is too small (5 mm), the electric field is too concentrated, causing the droplets to undergo intense polarization under the strong electric field. Although the particle size is smaller, the particle size distribution is uneven (large Span value), and abnormal discharge is prone to occur, resulting in a decrease in product yield. When the gap is too large (>60 mm), the droplets have already fallen a long distance before reaching the electrode ring. At this point, the surface moisture of the droplets has begun to evaporate, increasing the surface tension and hindering polarization dispersion. The optimal gap is 10~40 mm.

[0160] Table 4. Data on the effect of applied voltage

[0161] Voltage (kV) D50(μm) Span value Product yield (%) Encapsulation rate (%)* 0 32.5 1.85 97.0 72.3 -10 25.8 1.62 96.5 78.6 -20 18.2 1.45 96.2 86.4 -30 14.2 1.35 95.8 92.1 -40 12.5 1.38 94.5 93.5 -50 11.0 1.52 91.2 93.8 -60 10.2 1.68 86.5 92.5

[0162] *Note: Encapsulation efficiency data were obtained using a microcapsule system with vitamin E as the core material.

[0163] As shown in Table 4 above, when the applied voltage increases from 0 kV to -30 kV, the average particle size decreases significantly (from 32.5 μm to 14.2 μm), the particle size distribution narrows (Span decreases from 1.85 to 1.35), and the encapsulation efficiency increases dramatically (from 72.3% to 92.1%). This is a direct result of the Coulomb field polarization effect. Further increasing the voltage to -40 kV to -60 kV results in a further decrease in particle size, but the Span value increases (particle size distribution widens), and the product yield decreases. This is because excessively high electric field strength leads to excessive breakage of some droplets and the generation of extremely fine powder. Fine powder is easily entrained and lost by the airflow, and excessively high electric field strength may cause corona discharge and nitrogen ionization. Considering product particle size, uniformity, and yield, the optimal voltage is -20 kV to -40 kV.

[0164] Example 7: Long-term operational stability verification

[0165] (1) Experimental objective

[0166] This embodiment verifies the operational stability of the system under long-term continuous production conditions, the contamination resistance of the electrodes, and the consistency of product quality through continuous operation tests.

[0167] (2) Experimental conditions

[0168] The multi-ring stepped electrode system of Example 2 (three electrode rings, inner diameters of 30mm, 50mm, and 80mm, voltage -35kV) was used. The feed solution was probiotic microcapsule solution (same as in Example 5), the feed flow rate was 150mL / min, the drying inlet air temperature was 30℃, and the nitrogen flow rate was 700m³ / h. The system was run continuously for 8 hours (one regular production shift), with samples taken every 30 minutes to determine the viable bacteria count, moisture content, and particle size of the product. The experimental results are shown in Table 5 below.

[0169] Table 5 Results of Long-Term Operational Stability Tests

[0170] 0.5 8.5 3.8 15.2 Clean 1.0 8.6 3.6 15.5 Clean 2.0 8.4 3.7 15.8 Trace visible sediments 3.0 8.5 3.5 15.3 Trace visible sediments 4.0 8.3 3.8 15.6 Small amount of sediment 5.0 8.4 3.6 15.4 Small amount of sediment 6.0 8.2 3.7 15.7 Small amount of sediment 7.0 8.3 3.6 15.9 Small amount of sediment 8.0 8.2 3.8 15.5 Small amount of sediment

[0171] As shown in Table 5 above, the viable bacteria count of the product remained stable at (8.2~8.6)×10⁻⁶ during continuous operation for 8 hours. 9 The CFU / g concentration remained within a range (fluctuation <5%), the moisture content remained stable between 3.5% and 3.8% (fluctuation <0.3 percentage points), and the average particle size remained stable between 15.2 and 15.9 μm (fluctuation <5%). All indicators demonstrated good operational stability. Although a small amount of liquid splashed and deposited on the electrode ring surface, no significant electrode contamination or corrosion occurred, and no abnormal discharge was observed, indicating that the non-contact electrode configuration has good self-cleaning performance and long-term operational reliability. The product yield remained stable between 93% and 95% throughout the entire operation, with minimal adhesion to the tower wall, verifying the design advantage of the overall electrically neutral droplets of this invention. Therefore, the system and method of this invention can meet the stability requirements of continuous industrial production and have good engineering application prospects.

[0172] The following is in conjunction with the appendix Figure 2 and Figure 3 The working principle of the droplet polarization atomization low-temperature spray drying system and drying method based on the Coulomb field effect of this invention is described in detail.

[0173] (1) Physical basis of Coulomb field dielectric polarization

[0174] When a conductive or dielectric droplet is placed in an applied electric field, the free or bound charges inside the droplet redistribute under the influence of the electric field force. This phenomenon is called dielectric polarization. For a liquid system containing polar molecules (such as water molecules, organic molecules containing polar groups such as hydroxyl, carboxyl, and amino groups), the polar molecules are originally randomly oriented. Under the influence of an external strong electric field, the polar molecules undergo directional rotation and alignment along the direction of the electric field, and the centers of positive and negative charges of the molecules undergo relative displacement. This forms a macroscopic dipole moment along the direction of the electric field inside the droplet, inducing negative polarization charges on the droplet surface near the positive electrode and positive polarization charges on the droplet surface near the negative electrode. The additional electric field generated by the polarization charges on the droplet surface is opposite to the direction of the external electric field. When the external electric field is removed, the polarization charges disappear, and the droplet returns to an electrically neutral state.

[0175] One of the key innovations of this invention is that the droplet acquires polarization charge not through charge injection or transfer, but through dielectric polarization induction. The total positive and negative polarization charges are equal, and the droplet as a whole remains electrically neutral or nearly so. This feature fundamentally avoids the problem of electrostatic adsorption on the tower wall caused by the net charge on the droplet in existing electrostatic spraying technologies.

[0176] (2) Force and breakage mechanism of droplets in a non-uniform Coulomb field

[0177] In this invention, the Coulomb field generated by the electrode ring 310 or the conical ring electrode 320 has a non-uniform spatial distribution. Simultaneously, as the droplet is attracted to the electrode ring, the polarization charge on the droplet surface experiences an opposite electric force in the electric field, generating a deformation force that stretches the droplet along the direction of the electric field. When this stretching deformation force is sufficient to overcome the surface tension of the liquid, the droplet deforms and splits into smaller sub-droplets from its ends or edges.

[0178] (3) Coulomb field-induced formation mechanism of microcapsule shell-core structure

[0179] For microcapsule liquid systems containing shell and core materials (usually oil-in-water or water-in-water emulsions), the shell material is generally a water-soluble polar polymer (such as maltodextrin, gum arabic, modified starch, etc.), and the core material is generally a water-insoluble non-polar substance (such as oils, essential oils, vitamins, etc.).

[0180] Under the influence of a Coulomb electric field, polar shell molecules in the aqueous phase align themselves in a direction along the electric field, forming an ordered molecular layer. Due to the uneven distribution of the electric field on the droplet surface (stronger field near the electrode ring and weaker field away from the electrode ring), the polar molecules of the shell material migrate and accumulate in the region of higher electric field strength (i.e., the side of the droplet surface closer to the electrode ring) driven by the electric field gradient. This process is equivalent to forming an interface layer enriched with shell material molecules on the droplet surface, while the nonpolar molecules of the core material migrate into the droplet due to repulsion.

[0181] The electric field-driven molecular migration described above, in synergy with the traditional thermodynamically driven interfacial self-assembly process, enables the shell material to form a continuous protective outer shell on the droplet surface, with the core material encapsulated inside, thus spontaneously forming microcapsules with a regular shell-core structure. This process requires no additional emulsifiers or structure-inducing agents and is an electric field-assisted self-assembly process.

[0182] (4) The time scale of polarization relaxation and droplet neutrality

[0183] A droplet requires a certain relaxation time to reach a stable polarization state in a Coulomb field. The polarization relaxation time τ = εᵣ / σ, where ε is the vacuum permittivity, εᵣ is the relative permittivity, and σ is the conductivity. For typical aqueous solutions, the relaxation time τ is approximately 0.1–1.0 ms. The time it takes for the droplet to fall from the nozzle outlet and pass through the electrode ring is approximately 10–100 ms, much longer than the polarization relaxation time. Therefore, the droplet can reach a fully polarized state when passing through the electrode ring.

[0184] After the droplet leaves the electric field region of the electrode ring, under conditions without an external electric field, the polarization charge gradually disappears through the redistribution of free charges within the droplet and the thermal relaxation of polar molecules, with a relaxation time of approximately 0.1–1.0 ms. This means that the droplet returns to an electrically neutral state within a very short time after leaving the electrode ring. This characteristic ensures that the droplet carries no net charge during subsequent drying and separation processes, fundamentally avoiding adhesion to the tower wall and product loss caused by electrostatic adsorption.

[0185] In summary, the droplet polarization atomization low-temperature spray drying system and method based on the Coulomb field effect provided by this invention have wide industrial applicability and can be applied to the following fields: (1) Food industry: low-temperature drying and microencapsulation of heat-sensitive food ingredients such as probiotic live bacteria preparations, vitamin microcapsules, DHA / EPA fish oil microcapsules, flavor and fragrance microcapsules, natural pigment microcapsules, and instant coffee powder; (2) Pharmaceutical industry: low-temperature drying and powder preparation of biopharmaceutical products such as vaccines, enzyme preparations, bioactive proteins, nucleic acid drugs, liposomes, nanomedicines, and traditional Chinese medicine extracts; (3) Chemical industry: preparation of high-quality powder materials such as catalyst precursors, fine chemicals, functional material precursors, and MOF materials; (4) Ceramic industry: preparation of powder materials with special morphology requirements such as nano-ceramic powders, electronic ceramic materials, and structural ceramic precursors. Furthermore, the system of this invention can be modularly designed and scaled up. The processing capacity of a single set of equipment can be scaled up from laboratory scale (liquid flow rate 10~100mL / min) to industrial scale (liquid flow rate 100~2000L / h), demonstrating good feasibility for engineering scale-up.

[0186] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect, characterized in that, include: The liquid supply unit is used to deliver the liquid to be dried to the atomizing nozzle; Atomizing nozzles, with their nozzle outlets facing downwards, are used to initially atomize the liquid material into initial droplets; A high-voltage polarized electrode unit includes at least one electrode ring or conical ring electrode, which is coaxially arranged below the nozzle outlet of the atomizing nozzle and maintains a non-contact gap with the nozzle outlet, for generating a Coulomb electric field in the atomization region below the nozzle outlet. A high-voltage power supply, electrically connected to the high-voltage polarized electrode unit, is used to apply high-voltage direct current to the electrode ring or conical ring electrode; The drying tower, whose upper part is connected to the atomizing nozzle, is used to contain the atomized droplets after polarization treatment by the high-voltage polarized electrode unit and to contact the low-temperature drying medium to complete the drying. A low-temperature nitrogen circulating drying unit is connected to the drying tower and is used to supply low-temperature drying nitrogen to the drying tower and recycle it.

2. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to claim 1, characterized in that, The high-voltage polarized electrode unit includes a single electrode ring, wherein: The inner diameter of the electrode ring is 2 to 10 times the outlet diameter of the atomizing nozzle; The non-contact gap d between the electrode ring and the outlet of the atomizing nozzle is 5mm to 100mm, preferably 10mm to 50mm.

3. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to claim 1 or 2, characterized in that, The voltage applied by the high-voltage power supply to the electrode ring or the conical ring electrode is ±5kV to ±100kV.

4. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to any one of claims 1 to 3, characterized in that, The high-voltage polarized electrode unit includes multiple electrode rings arranged at intervals along the vertical direction, forming a multi-ring stepped electrode group, wherein: The spacing between adjacent electrode rings is 5mm to 80mm, and the diameter of each electrode ring increases or decreases sequentially from top to bottom.

5. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to claim 4, characterized in that, Each electrode ring in the multi-ring stepped electrode group is powered by either the same high-voltage power supply or an independently regulated high-voltage power supply, wherein: The voltage difference between adjacent electrode rings forms a gradient Coulomb field, causing the droplet to experience a gradually changing polarization electric field during its descent.

6. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to any one of claims 1 to 3, characterized in that, The high-voltage polarization electrode unit includes one of the conical ring electrodes, wherein: The inner diameter of the conical ring electrode gradually increases or decreases from top to bottom, and its cone angle α is 5°~60°; The axial height of the conical ring electrode is 20mm~150mm.

7. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to any one of claims 1 to 6, characterized in that, The electrode ring or the conical ring electrode is made of a conductive metal material, which is selected from stainless steel, titanium alloy, or brass, wherein: The surface of the electrode ring or the conical ring electrode is provided with an insulating coating, which is a polytetrafluoroethylene coating or a ceramic coating, and the thickness of the insulating coating is 0.05 mm to 2 mm.

8. The droplet polarization atomization low-temperature spray drying system based on the Coulomb field effect according to any one of claims 1 to 7, characterized in that, The low-temperature nitrogen circulating drying unit includes: A nitrogen heater / cooler for adjusting circulating nitrogen to a target drying temperature of -20°C to 100°C; A nitrogen circulation fan is used to drive the circulation of nitrogen within the system. A gas-solid separation device is used to separate dried powder particles from nitrogen gas; Solvent recovery condenser, used to condense and recover evaporated solvent carried in nitrogen gas; and Adsorption dryers are used for deep dehumidification of condensed nitrogen gas.

9. A method for low-temperature spray drying using droplet polarization atomization based on the Coulomb field effect, employing the system described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. The liquid material to be dried is pumped to the atomizing nozzle and initially atomized by the nozzle to form initial droplets. S2. The initial droplet is allowed to pass through the Coulomb electric field region generated by the electrode ring or conical ring electrode arranged below the nozzle outlet under the action of gravity, causing the droplet to further split and disperse into a group of polarized droplets with smaller particle size and more uniform distribution; at the same time, for microcapsule liquid containing shell material and core material, the Coulomb electric field causes the polar molecules of the shell material to be oriented and enriched towards the droplet surface, and the non-polar molecules of the core material to tend towards the interior of the droplet, spontaneously forming a shell-core microcapsule structure; S3. The polarized droplet group comes into contact with low-temperature drying nitrogen from the low-temperature nitrogen circulation drying unit in the drying tower, and the solvent evaporates to form dried powder particles. S4. The dried powder particles are collected by a gas-solid separation device to obtain the product; the moist nitrogen gas is condensed and the solvent is recovered by a solvent recovery condenser, and then returned to the drying tower for recycling after being deeply dehumidified by an adsorption dryer.

10. The method for low-temperature spray drying of droplet polarization atomization based on Coulomb field effect according to claim 9, characterized in that, The solid content of the liquid in step S1 is 10%~50%, the viscosity is 1~500mPa·s, the surface tension is 30~75mN / m, and the dielectric constant is 40~80. The Coulomb electric field strength generated by the electrode ring or the conical ring electrode in step S2 is 1×10⁻⁶. 5 ~5×10 6 V / m; The temperature of the low-temperature drying nitrogen gas in step S3 is -20℃ to 100℃.

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