Spray drying method for preparing vegetable fat powder

Abstract

The invention belongs to the technical field of spray drying, and particularly relates to a spray drying method for preparing non-dairy creamer, which comprises the following steps: homogenizing a non-dairy creamer raw material solution; carrying out atomization and gradient freezing processes on the pretreated raw material liquid to form solid particles; solid particles fall under the action of gravity and sequentially penetrate through the high-temperature area, the medium-temperature area and the low-temperature area along a spiral track, and gradual dehydration from the surface to the interior is completed; in the falling process of the solid particles, differential drying paths of the particles with different particle sizes are realized by regulating and controlling spatial distribution and retention time of the solid particles; discharging the dried powder, cooling, sieving and packaging; the problems of non-uniform drying caused by non-uniform particle size of liquid drops, caramelization reaction caused by local overheating and protein denaturation wall sticking are solved, and the quality of the non-dairy creamer is favorably improved.

Description

Technical Field

[0001] This invention belongs to the field of spray drying technology, specifically relating to a spray drying method for preparing plant lipid powder. Background Technology

[0002] Non-dairy creamer, also known as creamer or coffee creamer, is a microencapsulated powdered imitation dairy product made primarily from hydrogenated vegetable oil, with the addition of glucose syrup, sodium caseinate, emulsifiers, and stabilizers. Non-dairy creamer is typically produced using a spray-drying method. During spray drying, a precise transformation occurs from liquid emulsion droplets to solid microcapsule particles, a process involving a series of physical and chemical changes. When the emulsion is atomized into micron-sized droplets and enters the drying tower, the surface moisture of the droplets evaporates instantly upon contact with high-temperature hot air (typically 180-220°C), causing a rapid reduction in droplet surface area and a sharp rise in surface temperature. Simultaneously, due to the absorption of a large amount of latent heat during water evaporation, the core temperature of the droplets remains relatively low. As the moisture rapidly dissipates, the concentration of dissolved solids such as sugars and proteins in the continuous phase quickly rises to a supersaturated state, laying the foundation for subsequent solidification.

[0003] The problem with traditional spray dryers and drying methods in the production of non-dairy creamer lies in the difficulty of precisely controlling the droplet size distribution and uniformity of the atomization system. When high-pressure nozzles or centrifugal discs operate continuously in high-temperature and high-humidity environments, wear and scaling lead to a gradual deterioration of the atomization effect, producing a large number of droplets with uneven diameters. This non-uniformity directly results in significant differences in drying kinetics: small droplets dry instantly in high-temperature hot air to form a dense shell, while the internal moisture of large droplets evaporates later, remaining moist even after a hard shell forms on the surface, causing a "false drying" phenomenon. More seriously, the reducing sugars such as glucose and maltose in the non-dairy creamer raw materials undergo deep caramelization reactions in locally overheated areas (especially near the tower wall close to the hot air inlet). Sugar molecules begin to dehydrate and condense above 160°C, generating intermediate products such as hydroxymethylfurfural, which further polymerize to form dark brown melanoidins. Meanwhile, the protein components in the formula, such as sodium caseinate and whey protein, undergo irreversible denaturation under high-temperature shock, their molecular structures unfold and expose hydrophobic groups, forming a strongly adhesive complex with caramelization products, firmly adhering to the inner wall of the drying tower. This wall adhesion phenomenon has a cumulative amplification effect—the initially formed thin layer reduces the heat transfer efficiency of the tower wall, causing a further increase in local temperature, accelerating the caramelization and adhesion of subsequent materials, and ultimately forming a hard coke layer with a thickness of several millimeters. After prolonged operation, due to the reduction in the effective volume inside the tower, turbulent airflow distribution, and uneven particle residence time, the final product exhibits quality defects such as inconsistent color, decreased solubility, and poor oxidative stability. At the same time, the wall adhesion layer increases the thermal resistance of the equipment, leading to increased energy consumption, and requiring frequent shutdowns for high-pressure water cleaning or mechanical scraping, seriously affecting production continuity and equipment lifespan. In addition, potentially harmful substances such as acrylamide produced by the caramelization reaction may migrate into the product, posing food safety risks.

[0004] These technical defects highlight the limitations of traditional one-time high-temperature drying processes in the production of non-dairy creamer. Based on this, a spray drying method for the preparation of non-dairy creamer is proposed. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a spray drying method for preparing non-dairy creamer.

[0006] The objective of this invention can be achieved through the following technical solutions: The present invention provides a spray drying method for preparing plant lipid powder, comprising the following steps: S1: Raw material liquid pretreatment: Add trehalose to the raw material liquid of the non-dairy creamer and perform homogenization treatment; S2: Atomization and electrostatic loading: The pretreated raw material liquid is atomized, and the atomized droplets are charged by applying high voltage electrostatic charge. S3: Low-temperature solidification type: Charged droplets undergo a gradient freezing process from supercooling to complete solidification to form solid particles. S4: Gradient convection drying: Solid particles fall under the action of gravity and pass through the high temperature zone, medium temperature zone and low temperature zone in sequence along a spiral trajectory, completing the gradual dehydration from the surface to the inside; S5: Flow field control and graded drying: During the falling process of solid particles, the spatial distribution and residence time of solid particles are controlled by the combined effect of guiding the solid particles and the electrostatic charge on the solid particles, so as to realize the differentiated drying path of particles of different sizes. S6: Product collection and post-processing: Discharge the dried powder, cool it, sieve it and package it.

[0007] As a further aspect of the present invention, it includes a drying tower, and components arranged sequentially along the material processing flow within the drying tower: Atomization module: Located at the top of the drying tower, it is used to disperse the liquid raw material of non-dairy creamer containing reducing sugars and proteins into droplets; Low-temperature solidification module: It is arranged around the outlet of the atomizing module to perform gradient freezing treatment on the droplets, so that they are quickly solidified into solid particles with uniform internal structure, thereby eliminating the adhesion of materials in a wet state; Gradient convection drying module: Located in the middle and lower part of the drying tower, it is used to provide a horizontally surrounding hot air flow field with a temperature gradient distribution for the falling solid particles, so that they can complete deep dehydration during the spiral descent process; Particle flow field control module: Located inside the drying tower, it is used to control the spatial distribution and movement trajectory of solid particles in the tower through physical guidance and electrostatic repulsion, so as to prevent local accumulation and extend the effective drying time. Product collection module: Located at the bottom of the drying tower, used to collect the dried vegetable fat powder.

[0008] As a further embodiment of the present invention, the low-temperature solidification molding module includes a precooling unit and a cryogenic unit arranged in series along the vertical direction; the precooling unit is configured to provide a low-temperature environment of -10°C to 0°C, allowing the droplets to quickly enter a supercooled state and initially stabilize their morphology; the cryogenic unit is configured to provide a deep low-temperature environment of -25°C to -10°C, allowing the supercooled droplets to solidify rapidly and uniformly, forming solid particles with high specific surface area and porous structure, creating conditions for subsequent uniform heat and mass transfer.

[0009] As a further embodiment of the present invention, the gradient convection drying module includes a hot air and conveying unit; at least three layers of annular air ducts arranged tangentially along the height direction of the drying tower, respectively corresponding to the upper, middle and lower parts of the drying tower, and each layer of air ducts is independently connected to the hot air and conveying unit for introducing horizontal hot air into the tower to form a stable spiral upward or downward rotating flow field.

[0010] As a further embodiment of the present invention, the gradient convection drying module also includes a temperature control unit, which is configured to independently regulate the temperature of the hot air supplied by each layer of annular ducts, thereby forming a stepped temperature field of high temperature zone, medium temperature zone and low temperature zone from top to bottom in the drying tower. The high temperature zone has a temperature range of 150-170℃ and is used for rapid start-up drying; the medium temperature zone has a temperature range of 130-150℃ and is used for main body dehydration; the low temperature zone has a temperature range of 110-130℃ and is used for gentle dehumidification and to avoid heat damage.

[0011] As a further embodiment of the present invention, the particle flow field control module includes a central guide tube, which is a porous cylinder vertically suspended on the central axis of the drying tower, with a diameter of 1 / 5 to 1 / 2 of the tower diameter. The guide tube is configured to utilize the pressure difference generated by the rotating flow field inside the tower to guide lighter particles with smaller particle sizes to the core region of the tower, allowing them to slowly descend along a longer spiral path to ensure thorough drying. At the same time, it restricts larger particles to fall rapidly in an annular region outside the guide tube, realizing automatic particle classification and path optimization according to particle size.

[0012] As a further embodiment of the present invention, the particle flow field control module further includes a high-voltage electrostatic generation unit, whose electrodes are disposed at the atomization module or the feed pipeline, and is configured to apply a negative high-voltage electrostatic charge of 5kV to 15kV to the raw material liquid or the newly formed droplets, so that the surface of the formed solid particles carries the same charge; the Coulomb repulsion force is used to effectively suppress the collision, agglomeration and adsorption to the tower wall of the particles during the movement process, and maintain the particle dispersion state.

[0013] As a further aspect of the present invention, a raw material pretreatment module is also included, which is used to add trehalose accounting for 3%-10% of the total weight of the raw material liquid as a cryoprotectant.

[0014] As a further embodiment of the present invention, the hot air circulation system includes a heat pipe heat exchanger and a heat pump refrigeration unit; the heat pipe heat exchanger is installed in the exhaust pipe to recover the waste heat of the exhaust gas above 80°C for preheating fresh air; the heat pump refrigeration unit uses the heat exhaust of the drying system to drive the refrigeration cycle and provide cooling capacity for the low-temperature condensation zone.

[0015] As a further embodiment of the present invention, a 1-2 meter long heat recovery section is provided at the bottom of the gradient drying tower; the heat recovery section relies on the residual heat carried by the particles themselves after drying to complete the final moisture evaporation.

[0016] The beneficial effects of this invention are as follows: By changing the traditional "high-temperature instantaneous drying" mode, a "low-temperature curing combined with gradient drying" process route is adopted. In S1, trehalose acts as a low-temperature protectant to stabilize the emulsion interface; in S2, electrostatic charge causes particles to repel each other; in S3, gradient freezing avoids ice crystal damage and completely eliminates wet adhesion; in S4, temperature gradient distribution achieves uniform dehydration from the surface to the interior; in S5, flow field control ensures that particles of different sizes obtain the optimal drying path; and in S6, gentle post-treatment maintains product quality. The entire process solves the technical problems of uneven drying caused by uneven droplet size, caramelization reaction caused by local overheating, and protein denaturation and adhesion to the wall in traditional methods. Attached Figure Description

[0017] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 This is a flowchart of the steps of the present invention. Detailed Implementation

[0019] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided.

[0020] like Figure 1 As shown, a spray drying method for preparing plant lipid powder according to the present invention includes the following steps: S1: Raw material liquid pretreatment: Add trehalose to the raw material liquid of the non-dairy creamer and perform homogenization treatment; S2: Atomization and electrostatic loading: The pretreated raw material liquid is atomized, and the atomized droplets are charged by applying high voltage electrostatic charge. S3: Low-temperature solidification type: Charged droplets undergo a gradient freezing process from supercooling to complete solidification to form solid particles. S4: Gradient convection drying: Solid particles fall under the action of gravity and pass through the high temperature zone, medium temperature zone and low temperature zone in sequence along a spiral trajectory, completing the gradual dehydration from the surface to the inside; S5: Flow field control and graded drying: During the falling process of solid particles, the spatial distribution and residence time of solid particles are controlled by the combined effect of guiding the solid particles and the electrostatic charge on the solid particles, so as to realize the differentiated drying path of particles of different sizes. S6: Product collection and post-processing: Discharge the dried powder, cool it, sieve it and package it.

[0021] By changing the traditional "high-temperature instantaneous drying" mode, a "low-temperature curing combined with gradient drying" process route is adopted. In S1, trehalose acts as a low-temperature protectant to stabilize the emulsion interface; in S2, electrostatic charge causes particles to repel each other; in S3, gradient freezing avoids ice crystal damage and completely eliminates wet adhesion; in S4, temperature gradient distribution achieves uniform dehydration from the surface to the interior; in S5, flow field control ensures that particles of different sizes obtain the optimal drying path; and in S6, gentle post-treatment maintains product quality. The entire process fundamentally solves the technical problems of uneven drying caused by uneven droplet size, caramelization reaction caused by local overheating, and protein denaturation and adhesion to the wall in traditional methods.

[0022] As a further aspect of the present invention, it includes a drying tower, and components arranged sequentially along the material processing flow within the drying tower: Atomization module: Located at the top of the drying tower, it is used to disperse the liquid raw material of non-dairy creamer containing reducing sugars and proteins into droplets; Low-temperature solidification module: It is arranged around the outer periphery of the outlet of the atomizing module to perform gradient freezing treatment on the droplets, so that they are quickly solidified into solid particles with uniform internal structure, thereby eliminating the adhesion of materials in a wet state; Gradient convection drying module: Located in the middle and lower part of the drying tower, it is used to provide a horizontally surrounding hot air flow field with a temperature gradient distribution for the falling solid particles, so that they can complete deep dehydration during the spiral descent process; Particle flow field control module: Located inside the drying tower, it is used to control the spatial distribution and movement trajectory of solid particles in the tower through physical guidance and electrostatic repulsion, so as to prevent local accumulation and extend the effective drying time. Product collection module: Located at the bottom of the drying tower, it is used to collect the dried vegetable fat powder.

[0023] Modular design achieves spatial separation and functional integration of the process flow. The atomization module generates droplets at the top; the low-temperature condensation module immediately eliminates the wet viscosity of the material; the gradient convection drying module provides precise temperature distribution; the particle flow field control module optimizes particle trajectory; and the product collection module efficiently separates the finished product. These modules work together to enable the material to complete the phase change process from liquid to solid to dry powder within the drying tower, avoiding the problem of droplets sticking to the walls under high temperature and humidity conditions found in traditional equipment. Simultaneously, spatial segmentation control ensures uniform drying.

[0024] As a further embodiment of the present invention, the cryogenic solidification module includes a precooling unit and a cryogenic unit arranged in series along the vertical direction; the precooling unit is configured to provide a low-temperature environment of -10°C to 0°C, so that the droplets quickly enter the supercooled state and initially stabilize their shape; the cryogenic unit is configured to provide a deep low-temperature environment of -25°C to -10°C, so that the supercooled droplets quickly and uniformly solidify completely, forming solid particles with high specific surface area and porous structure, creating conditions for subsequent uniform heat and mass transfer.

[0025] The precooling unit uses a double-helix copper tube surrounding the atomizing head outlet, through which a -5°C ethylene glycol solution is introduced, causing droplets to remain in this area for 0.8 seconds. The cryogenic unit uses a stainless steel finned tube heat exchanger, through which a -18°C liquid nitrogen / ethanol mixed refrigerant is introduced, causing droplets to remain in this area for 1.5 seconds. Temperature control accuracy is ±1°C, and cooling rates reach 50°C / s and 120°C / s, respectively. Droplets in the precooling unit reach a supercooled state at -3°C on the surface and completely solidify at the core temperature of the cryogenic unit, which reaches -15°C.

[0026] Gradient freezing addresses the structural damage caused by rapid freezing by controlling the ice crystal nucleation and growth process. The pre-cooling unit rapidly cools the droplet surface to create a supercooled state, inhibiting the simultaneous nucleation of numerous ice crystals. The cryogenic unit, building upon this supercooling, achieves uniform and rapid solidification, forming a fine and uniform ice crystal structure. This staged freezing avoids stress cracking caused by excessive internal and external temperature differences in traditional single-stage freezing. Simultaneously, trehalose acts as a cryoprotectant, forming a protective film on the ice crystal surface, maintaining the integrity of the emulsion interface and providing a structurally stable solid particle foundation for subsequent drying.

[0027] As a further embodiment of the present invention, the gradient convection drying module includes a hot air and conveying unit; at least three layers of annular air ducts arranged tangentially along the height direction of the drying tower, corresponding to the upper, middle and lower parts of the drying tower respectively, and each layer of air ducts is independently connected to the hot air and conveying unit for introducing horizontal hot air into the tower to form a stable spiral upward or downward rotating flow field.

[0028] The upper layer of the three-layer annular duct is located 0.8m below the top of the tower, the middle layer is located 2.5m below, and the lower layer is located 4.2m below. The tangential angle of each layer of duct is 45°. The outlet of the duct of the hot air and conveying unit is equipped with adjustable guide vanes to control the airflow angle to be adjustable by ±15°. The measured wind speed distribution is: 18m / s for the upper layer, 15m / s for the middle layer, and 12m / s for the lower layer, forming a stable downward spiral flow field.

[0029] The tangentially arranged annular ductwork utilizes fluid dynamics principles to create a rotating flow field for the hot air within the tower. After entering through the tangential inlet, the hot air is constrained by the tower wall and moves circumferentially, simultaneously forming a spiral trajectory under the influence of gravity and centrifugal force. This flow field structure causes solid particles to rotate during their descent, extending their residence time and ensuring uniform exposure to the hot air. The three-layer independent duct design allows for different air velocities and volumes at different heights, adapting to the heat and mass transfer requirements of particles at different drying stages and avoiding the uneven drying problems caused by traditional single-stage air inlets.

[0030] As a further embodiment of the present invention, the gradient convection drying module also includes a temperature control unit, which is configured to independently regulate the temperature of the hot air supplied by each layer of annular ducts, thereby forming a stepped temperature field of high temperature zone, medium temperature zone and low temperature zone from top to bottom in the drying tower. The high temperature zone has a temperature range of 150-170℃ and is used for rapid start-up drying; the medium temperature zone has a temperature range of 130-150℃ and is used for main body dehydration; the low temperature zone has a temperature range of 110-130℃ and is used for gentle dehumidification and to avoid heat damage.

[0031] The stepped temperature field design conforms to the material drying kinetics. The high-temperature zone (150-170℃) provides high heat transfer driving force, rapidly evaporating moisture from the particle surface and forming a dense protective layer on the particle surface to prevent surface hardening caused by excessively rapid migration of internal moisture. The medium-temperature zone (130-150℃) maintains a moderate drying rate, allowing internal moisture to diffuse evenly outward and avoiding "false drying." The low-temperature zone (110-130℃) employs mild drying conditions to remove residual bound water while preventing thermal degradation of heat-sensitive components. This temperature distribution effectively controls the degree of Maillard reaction, avoiding deep caramelization of reducing sugars at high temperatures and ensuring the stability of product color and flavor.

[0032] As a further embodiment of the present invention, the particle flow field control module includes a central guide tube, which is a porous cylinder vertically suspended on the central axis of the drying tower, with a diameter of 1 / 5 to 1 / 2 of the tower diameter. The guide tube is configured to utilize the pressure difference generated by the rotating flow field inside the tower to guide lighter particles with smaller particle sizes to the core region of the tower, allowing them to slowly descend along a longer spiral path to ensure thorough drying. At the same time, it restricts larger particles to fall rapidly in an annular region outside the guide tube, realizing automatic particle classification and path optimization according to particle size.

[0033] Its core working principle is to utilize the radial pressure difference generated in the rotating flow field and the inertial difference of the particles themselves to achieve automatic particle sorting and path planning. When hot air enters tangentially from the tower wall, it forms a high-speed rotating spiral upward or downward airflow field inside the tower. According to the principles of fluid mechanics, the static pressure at the center (axis) of this rotating flow field is lower than the static pressure near the tower wall, forming a radial pressure gradient from the tower wall to the center.

[0034] When solid particles of different sizes fall into this flow field, they are subjected to gravity, airflow drag, and a centripetal force generated by the pressure gradient. Small or light particles, due to their small mass and low inertia, are more easily entrained by the airflow and are more significantly affected by the radial pressure gradient force. Therefore, they are "sucked" into the low-pressure central region and enter the central guide tube with part of the rising airflow. Large or heavy particles, due to their large mass and high inertia, are mainly driven by gravity and are less likely to have their direction significantly changed by the radial airflow. Therefore, they rely on their initial momentum and fall directly into the annular region between the guide tube and the tower wall.

[0035] Small particles entering the guide tube are constrained by the tube wall and affected by the complex turbulence and potentially slow-moving upward airflow within the tube, resulting in a significantly slower descent speed. They undergo a longer, more tortuous spiral path within the tube, extending their residence time and achieving gentle, thorough deep drying, avoiding the phenomenon of "false drying." Larger particles in the annular region, due to the high airflow velocity and fast tangential velocity in this area, descend along the spiral at a relatively faster speed, with a shorter residence time. However, because of their large particle size, the path for moisture to migrate from the interior to the surface is long, requiring a higher hot air temperature to ensure drying efficiency. This region corresponds precisely to the high-temperature zone near the tower wall, meeting this requirement.

[0036] As a further embodiment of the present invention, the particle flow field control module also includes a high-voltage electrostatic generation unit, whose electrodes are set at the atomization module or the feed pipeline, and are configured to apply a negative high-voltage electrostatic charge of 5kV to 15kV to the raw material liquid or the newly formed droplets, so that the surface of the formed solid particles carries the same charge; the Coulomb repulsion force is used to effectively suppress the collision, agglomeration and adsorption to the tower wall of the particles during the movement process, and maintain the particle dispersion state.

[0037] High-voltage electrostatics suppress interparticle interactions through Coulomb repulsion. When droplets pass through the high-voltage electric field, their surfaces acquire negative charges, which are "frozen" on the particle surface upon solidification. The repulsive force generated by like charges prevents particles from agglomerating during collisions. Simultaneously, charged particles generate dielectric force under the influence of the electric field, moving them away from the grounded metal tower wall and reducing wall deposition. Electrostatic repulsion also alters the particle distribution density in the airflow, increasing the interparticle spacing and improving hot air penetration efficiency. This synergistic effect of electrostatic and flow field control significantly improves particle dispersion, solving the problems of uneven drying and tower wall adhesion caused by particle agglomeration in traditional drying processes.

[0038] As a further aspect of the invention, a raw material pretreatment module is also included. This module is used to add trehalose, accounting for 3%-10% of the total weight of the raw material liquid, as a cryoprotectant. Trehalose functions as a cryoprotectant through multiple mechanisms. Its molecular structure contains multiple hydroxyl groups, which can form strong hydrogen bonds with water molecules, lowering the freezing point of water and inhibiting ice crystal growth. During freezing, trehalose forms a protective layer at the ice crystal-solution interface, preventing ice crystals from piercing the oil droplet interface film.

[0039] As a further embodiment of the present invention, the hot air circulation system includes a heat pipe heat exchanger and a heat pump refrigeration unit; the heat pipe heat exchanger is installed in the exhaust pipe to recover the waste heat of the exhaust gas above 80°C for preheating fresh air; the heat pump refrigeration unit uses the heat discharged from the drying system to drive the refrigeration cycle and provide cooling capacity for the low-temperature condensation zone.

[0040] As a further embodiment of the present invention, a 1-2 meter long heat recovery section is provided at the bottom of the gradient drying tower; the heat recovery section relies on the residual heat carried by the particles themselves after drying to complete the final moisture evaporation.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A spray drying process for the preparation of a fat bloom-preventing powder, characterized in that: The method comprises the following steps: S1: raw material liquid pretreatment: adding trehalose in the cottonseed kernel meal raw material liquid and performing homogenization treatment; S2: atomization and electrostatic loading: atomizing the pretreated raw material liquid, and charging the atomized liquid droplets by applying high voltage electrostatic; S3: low-temperature coagulation and solidification: making the charged liquid droplets sequentially undergo a gradient freezing process from supercooling to complete solidification to form solid particles; S4: gradient convection drying: the solid particles fall along a spiral trajectory and sequentially pass through high-temperature, medium-temperature and low-temperature zones under the action of gravity to complete progressive dehydration from the surface to the inside; 2. A spray drying process for the preparation of fat-encrusted flour according to claim 1, characterized in that: S5: flow field regulation and graded drying: during the falling of the solid particles, the spatial distribution and residence time of the solid particles are regulated by the combined action of the guiding of the solid particles and the static electricity carried by the solid particles, so that the different particle sizes of the particles realize differential drying paths; S6: product collection and post-treatment: discharging the dried powder and performing cooling, sieving and packaging. The method comprises a drying tower and the following modules arranged in sequence along the material processing flow in the drying tower: an atomization module: arranged at the top of the drying tower, used for dispersing the cottonseed kernel meal raw material liquid containing reducing sugar and protein into liquid droplets; a low-temperature coagulation and solidification module: arranged around the outlet of the atomization module, used for gradient freezing treatment of the liquid droplets to rapidly solidify them into solid particles with uniform internal structure, thereby eliminating the adhesion of the material in the wet state; a gradient convection drying module: arranged in the middle and lower part of the drying tower, used for providing a horizontal surrounding and temperature step distribution hot air flow field for the falling solid particles, so that they complete deep dehydration in the spiral descending process; 3. A spray drying process for the preparation of fat-encrusted ends according to claim 2, characterized in that: a particle flow field regulation module: arranged inside the drying tower, used for regulating the spatial distribution and motion trajectory of the solid particles in the tower by physical flow guiding and electrostatic repulsion, preventing local accumulation and prolonging the effective drying time; 4. A spray drying process for the preparation of fat-encrusted end product according to claim 2, characterized in that: a product collection module: arranged at the bottom of the drying tower, used for collecting the dried cottonseed kernel meal powder. The low-temperature coagulation and solidification module comprises a pre-cooling unit and a deep cooling unit arranged in series along the vertical direction; the pre-cooling unit is configured to provide a low-temperature environment of-10℃ to 0℃, so that the liquid droplets rapidly enter the supercooling state and preliminarily stabilize the morphology; the deep cooling unit is configured to provide a deep low-temperature environment of-25℃ to-10℃, so that the supercooled liquid droplets rapidly and uniformly completely solidify to form solid particles with high specific surface area and pore structure, creating conditions for subsequent uniform heat and mass transfer. The gradient convection drying module comprises a hot air and conveying unit; at least three layers of annular air pipes arranged tangentially along the height direction of the drying tower correspond to the upper, middle and lower parts of the drying tower, respectively, and each layer of air pipe is independently connected to the hot air and conveying unit for introducing horizontal hot air into the tower to form a stable spiral upward or downward rotating flow field.

5. A spray drying process for the preparation of fat-encrusted ends according to claim 4, characterized in that: The gradient convection drying module further comprises a temperature control unit configured to independently regulate the temperature of the hot air sent by each layer of annular air duct, thereby forming a stepped temperature field of high temperature zone, medium temperature zone and low temperature zone from top to bottom in the drying tower, wherein the temperature range of the high temperature zone is 150-170℃, which is used for rapid start-up drying; the medium temperature zone is 130-150℃, which is used for main dehydration; the low temperature zone is 110-130℃, which is used for mild moisture reduction and to avoid thermal damage.

6. A spray drying process for the preparation of fat- coated powders according to claim 2, characterized in that: The particle flow field regulation module comprises a central flow guide cylinder, which is a perforated cylinder vertically suspended on the central axis of the drying tower, with a diameter of 1 / 5 to 1 / 2 of the tower diameter; the flow guide cylinder is configured to use the pressure difference generated by the rotating flow field in the tower to guide the particles with lighter mass and smaller particle size to the core area of the tower, so that they slowly descend along a longer spiral path, ensuring sufficient drying; at the same time, the particles with larger mass are limited to the annular area outside the flow guide cylinder to quickly fall, realizing automatic classification and path optimization of particles according to particle size.

7. A spray drying process for the preparation of fat coated powders according to claim 6, characterized in that: The particle flow field regulation module further comprises a high-voltage electrostatic generation unit, whose electrodes are arranged at the atomization module or the feed pipe, configured to apply a negative high-voltage electrostatic of 5kV to 15kV to the raw material liquid or newly formed droplets, so that the surface of the formed solid particles carries the same charge; the coulomb repulsion is used to effectively inhibit the collision, agglomeration and adsorption to the tower wall of the particles during movement, maintaining the dispersed state of the particles.

8. A spray drying process for the preparation of fat- coated powders according to claim 2, characterized in that: It further comprises a raw material pretreatment module, which is used to add trehalose as a cryoprotective agent accounting for 3%-10% of the total weight of the raw material liquid in the raw material liquid.

9. A spray drying process for the preparation of fat-encrusted end product according to claim 2, characterized in that: The hot air circulation system comprises a heat pipe heat exchanger and a heat pump refrigeration unit; the heat pipe heat exchanger is installed in the exhaust pipe to recover the waste heat of exhaust gas above 80℃ for preheating fresh air; the heat pump refrigeration unit uses the exhaust heat of the drying system to drive the refrigeration cycle to provide cold energy for the low-temperature solidification zone.

10. A spray drying process for the preparation of fat- coated powders according to claim 2, characterized in that: The gradient drying tower is provided with a heat preservation and waste heat recovery section at the bottom; the heat preservation section completes the final moisture evaporation by relying on the residual heat carried by the dried particles themselves.

Images