Bean product low-temperature drying method based on heat exchange technology

Abstract

The invention discloses a bean product low-temperature drying method based on a heat exchange technology, and aims to solve the problems that nutrition retention and efficiency are difficult to consider and the quality stability is poor in the prior art. The method comprises the following steps: pre-treating and dishing bean products, sealing and vacuumizing a vacuum tank, constructing a heat exchange field by dry ice surrounding and hot nitrogen convection, optimizing a molecular structure through electrode induction, dynamically regulating and controlling parameters for drying, condensing and draining water, and post-treating. Efficient heat exchange is formed between dry ice outside the vacuum tank and hot nitrogen in the tank, and a low-temperature environment of 35-40 DEG C is maintained; the protein structure is improved through electrode induction, and flavor is stimulated; and dynamically adjusting nitrogen parameters to adapt to the change of the water content. The method is low in energy consumption, can retain more than or equal to 90% of protein, and the dried bean product is uniform in water content (error is less than or equal to 1%), good in texture and flavor and suitable for industrial large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of drying technology and relates to a low-temperature drying method for soybean products based on heat exchange technology. Background Technology

[0002] Soy products, as an important category of traditional fermented foods, are rich in high-quality plant protein, bioactive peptides, and various bioactive substances. Drying is a crucial process for ensuring product storage stability and extending shelf life. Currently, the main technologies used in soy product drying include traditional hot air drying, conventional low-temperature drying, and vacuum drying. Traditional hot air drying achieves dehydration through forced convection of high-temperature hot air (60-80℃). However, high temperatures can easily cause denaturation and inactivation of heat-sensitive nutrients in soy products (such as soy isoflavones and active enzymes), while also damaging protein structures, leading to problems such as rough texture and flavor loss. Furthermore, uneven humidity distribution during the drying process can easily result in localized over-drying or under-drying, affecting product quality consistency.

[0003] While conventional low-temperature drying technology controls the temperature at 40-60℃ to retain some active substances, it suffers from low drying efficiency and high energy consumption. Because the rate of moisture evaporation is slow at low temperatures, the drying time needs to be extended (usually 8-12 hours), which not only increases energy consumption but also may lead to microbial growth in soy products due to prolonged exposure to a warm environment, posing a safety hazard. Furthermore, traditional low-temperature drying often uses a single temperature field and a static drying mode, failing to dynamically adjust drying parameters according to changes in the moisture content of the soy products. This results in poor internal moisture migration, leading to a "dry outside, wet inside" situation and reduced product storage stability.

[0004] Vacuum drying technology lowers the boiling point of water by reducing ambient air pressure, achieving low-temperature dehydration. While this can preserve some of the nutrients in soy products, it involves large equipment investments, complex operations, and a lack of effective heat exchange mechanisms during the drying process, resulting in low heat transfer efficiency and limited production capacity, making it difficult to meet the demands of large-scale industrial production. Furthermore, existing vacuum drying technologies are not optimized for the molecular structure of soy products, resulting in products that are hard, lack elasticity, and have poor flavor retention, failing to meet consumer demand for high-quality soy products.

[0005] In summary, existing soybean product drying technologies generally suffer from the main problems of "difficulty in balancing nutrient retention and drying efficiency, poor product quality stability, and high energy consumption." There is an urgent need to develop a new low-temperature drying method that combines efficient dehydration, nutrient retention, and quality optimization to solve the industry's technical bottlenecks. Summary of the Invention

[0006] This invention provides a low-temperature drying method for soybean products based on heat exchange technology to solve the aforementioned background technical problems.

[0007] The technical solution of this invention is: A low-temperature drying method for soybean products based on heat exchange technology, the drying method is as follows: Step 1: Pre-processing and plating of soy products Select fresh soy products, remove surface impurities and excess moisture, and cut or shape them according to the type of soy product (such as tofu, dried tofu, and bean curd sticks) to ensure uniform size of individual pieces (error not exceeding 5%). Spread the processed soy products evenly on a high-temperature resistant tray with ventilation holes, and place a silicone heat-conducting pad at the bottom of the tray. The stacking height of the soy products should not exceed 3cm to avoid squeezing between layers and affecting moisture diffusion. Step 2: Vacuum Can Pretreatment and Sealing; Place the tray containing the bean products into the stainless steel vacuum can, with the trays layered by the support, maintaining a 15cm gap between layers to ensure smooth airflow inside the can; Close the vacuum can door, start the vacuum pump, reduce the air pressure inside the can to 50-100Pa, maintain for 30 minutes, and remove the air inside the can and residual gas in the gaps between the bean products. Step 3: Dry ice surround arrangement and heat exchange system start-up; install a heat insulation sleeve on the outside of the vacuum tank, forming a 5cm wide annular cavity between the insulation sleeve and the outer wall of the vacuum tank, and uniformly fill the cavity with dry ice to ensure full contact between the dry ice and the outer wall of the vacuum tank, maintaining the low temperature environment outside the tank (-20℃ to -15℃); at the same time, start the hot nitrogen supply system inside the tank, heat the nitrogen to 45-50℃ through the nitrogen preheating device, and uniformly introduce it into the vacuum tank through the annular gas distribution pipe inside the tank at a gas flow rate of 0.5-1m³ / h, forming a hot nitrogen convection field in the low temperature environment inside the tank; Step 4: Electrode induction treatment and molecular structure optimization; Two sets of platinum electrode plates are symmetrically arranged in a vacuum chamber, with a distance of 8-10 cm between the electrode plates and the surface of the soy products. A high-frequency pulse power supply is turned on to apply a pulsed electric field with a voltage of 5-10 kV and a frequency of 10-20 kHz to the electrode plates. The electrode induction process lasts for 60 minutes, during which the surface potential changes of the soy products are monitored in real time to ensure that the electric field uniformly covers all materials. The electric field improves the internal cross-linking structure of the protein molecules in the soy products, enhances molecular stability, and stimulates the transformation of flavor precursor substances. Step 5: Dynamic heat exchange drying and parameter control; continuously introduce hot nitrogen and maintain the internal pressure of the tank at 50-100 Pa. Monitor the surface temperature of the soybean products in real time using an internal temperature sensor to ensure the temperature remains stable at 35-40℃; dynamically adjust the nitrogen introduction rate and temperature according to the moisture content of the soybean products. In the initial stage (moisture content 40%-60%), maintain the nitrogen temperature at 45℃ and the aeration rate at 1 m³ / h; in the middle stage (moisture content 20%-40%), adjust to a nitrogen temperature of 42℃ and an aeration rate of 0.8 m³ / h; in the final stage (moisture content 10%-20%), adjust to a nitrogen temperature of 40℃ and an aeration rate of 0.5 m³ / h; replenish dry ice to the annular cavity in real time using a dry ice replenishment device to maintain a stable low-temperature environment outside the tank. Step 6: Humidity Monitoring and Condensation Drainage; Activate the in-tank condensation recovery system, which condenses the moisture evaporated from the hot nitrogen into liquid water through the condensation coils built into the tank wall. The temperature of the condensation coils is controlled between 0-5℃, and the condensate flows into the storage tank through the collection pipe. Monitor the humidity of the nitrogen in the tank in real time using a humidity sensor. When the humidity exceeds 30%, activate the nitrogen purification device to dehumidify and filter the circulating nitrogen before re-introducing it into the tank, ensuring that the humidity of the drying environment is stable between 10%-30%. Step 7: Drying Termination and Post-processing; When the moisture content of the soy products drops to 8%-12% (detected by the built-in moisture sensor, with a fluctuation of no more than 0.5% over 15 consecutive minutes), stop the supply of hot nitrogen and the electrode induction device; turn off the vacuum pumping system and slowly introduce dry air into the tank to gradually restore the pressure inside the tank to normal pressure (the restoration rate is 10Pa / min to avoid sudden pressure changes that could damage the structure of the soy products); open the vacuum tank door, remove the soy products, and place them in a constant temperature and humidity environment of 25℃ and 50% relative humidity for 30 minutes to cool, thus completing the drying process.

[0008] Furthermore: In step 1, the pretreated soy products need to undergo surface spraying treatment. The spraying solution is a mixed aqueous solution of 0.5% salt and 0.3% vitamin C, with a spraying volume of 0.1L per 1kg of soy products. After spraying, the product is left to stand for 15 minutes. Through electrolyte adjustment and antioxidant treatment, the stability and flavor retention rate of the soy products during the drying process are further improved. The diameter of the ventilation holes in the tray is 2mm, the spacing between the holes is 5mm, and they are distributed in a regular hexagonal pattern to ensure that hot nitrogen gas penetrates the material layer evenly. The thickness of the silicone heat-conducting pad is 3mm, and the thermal conductivity is ≥0.8W / (m・K), which enhances the heat transfer efficiency between the tray and the soy products.

[0009] Furthermore, in step 2, the vacuum tank adopts a double-layer stainless steel structure, with the inner layer made of 316L stainless steel and the outer layer made of 304 stainless steel. The space between the two layers is filled with polyurethane insulation material (10cm thick, thermal conductivity ≤0.02W / (m・K)). The vacuum pumping device uses two-stage vacuum pumps connected in series. The first stage is a rotary vane vacuum pump, which reduces the air pressure to 1000Pa. The second stage is a diffusion pump, which further reduces the pressure to 50-100Pa. During the pumping process, the air pressure inside the tank is monitored in real time by a vacuum gauge to ensure that the air pressure control accuracy error does not exceed 5Pa.

[0010] Furthermore: In step 3, food-grade solid carbon dioxide with a purity of ≥99.9% is used as dry ice. During the filling process, the temperature inside the annular cavity is monitored in real time by a temperature sensor. When the temperature is higher than -15℃, the automatic replenishment device is activated to add dry ice. The nitrogen preheating device uses an electric heating heat exchanger with a heating power of 5kW and is equipped with a temperature feedback control system to ensure that the nitrogen outlet temperature fluctuation does not exceed ±1℃. The annular gas distribution pipe has evenly distributed gas outlets with a diameter of 1mm, and the gas outlets are oriented at a 45° angle to the tray surface to form a spiral airflow, which enhances the uniformity of heat exchange.

[0011] Furthermore, in step 4, the platinum electrode plate is coated with a titanium nitride coating with a thickness of 5μm to enhance the electrode's corrosion resistance and electric field stability; the high-frequency pulse power supply is equipped with an electric field uniformity detection module, which monitors the electric field strength inside the tank in real time through multiple sampling points to ensure that the electric field strength distribution error does not exceed 10%; during the electrode induction process, the temperature change of the bean product is monitored simultaneously, and if the temperature exceeds 40℃, the pulse voltage is automatically reduced by 0.5kV to avoid local overheating affecting product quality.

[0012] Furthermore, in step 5, the moisture content of the soy products is detected in real time using a microwave moisture sensor installed on the top of the vacuum tank. The sensor performs multi-point detection on the soy products on each tray every 10 minutes (5 points are detected on each tray). The detection data is transmitted to the central control system, which automatically generates a moisture content change curve and then dynamically adjusts the nitrogen parameters. The hot nitrogen circulation system is equipped with a high-efficiency heat exchanger to recover the waste heat of the nitrogen discharged during the drying process and use it to preheat the newly introduced nitrogen. The waste heat recovery rate is ≥60%, reducing energy consumption.

[0013] Furthermore: In step 6, the condenser coil is made of copper-nickel alloy and is spirally distributed on the inner wall of the vacuum tank, with a total heat exchange area of ​​≥2m²; the condensate collection pipe is made of stainless steel and equipped with a filter (filtration accuracy 1μm) to remove trace impurities from the condensate; the nitrogen purification device uses molecular sieve desiccant (model 3A) with a dehumidification efficiency of ≥95% and the purified nitrogen dew point ≤-40℃ to ensure the low humidity requirements of the drying environment.

[0014] Furthermore: In step 7, the moisture sensor adopts the capacitive measurement principle, with a measurement range of 0-100% and a measurement accuracy of ±0.5%. The sensor probe is in direct contact with the surface of the bean product, and the moisture content is calculated by multi-point averaging. During the cooling process, a gradient cooling method is adopted, first cooling at 25℃ for 15 minutes and then transferring to 20℃ for 15 minutes to avoid cracking of the bean product due to excessive temperature difference. After drying, the bean product needs to undergo quality testing, including indicators such as moisture uniformity (error ≤1%), protein retention rate (≥90%), and hardness (20-30N). Only after passing the tests can it be stored in the warehouse.

[0015] The beneficial effects of this invention patent: 1. Highly efficient and balanced low-temperature drying and nutrient retention: By constructing a heat exchange field through dry ice (-20℃ to -15℃) outside the vacuum tank and hot nitrogen (45-50℃) inside the tank, combined with a vacuum environment (50-100Pa), the surface temperature of soy products is stabilized at 35-40℃. This avoids high-temperature damage to heat-sensitive components and accelerates moisture evaporation through heat convection, solving the problem of low efficiency in traditional low-temperature drying. Ultimately, it can retain ≥90% of protein and active substances such as soy isoflavones, with a nutrient retention rate that is more than 20% higher than that of traditional hot air drying.

[0016] 2. Enhance product quality stability and flavor: Electrode-induced treatment (5-10kV pulsed electric field) optimizes the cross-linking structure of protein molecules in soy products, enhancing texture stability and reducing cracking after drying; simultaneously, it stimulates the conversion of flavor precursors, improving product flavor. Furthermore, by dynamically adjusting nitrogen parameters to adapt to changes in moisture content, combined with a uniform heat exchange design, the moisture content error of dried soy products is ≤1%, avoiding "dry outside, moist inside," and extending the shelf life by more than 3 months.

[0017] 3. Reduced energy consumption and improved industrial adaptability: The waste heat recovery rate of hot nitrogen is ≥60%, and the low temperature environment of dry ice reduces heat loss, resulting in an overall energy consumption reduction of 35% compared to conventional low temperature drying. All process parameters can be automatically controlled by sensors and control systems without extensive manual intervention. Furthermore, the layered design of the vacuum tank is suitable for a capacity of 8-12 tons / day, meeting the needs of large-scale industrial production and solving the problem of limited capacity in traditional vacuum drying.

[0018] 4. Ensuring production safety and ease of operation: The pretreatment stage features spraying antioxidant liquid, condensate drainage, and nitrogen purification design to prevent microbial growth and impurity residue; pressure recovery rate control (10Pa / min) and gradient cooling process prevent damage to the structure of soy products; real-time monitoring and automatic compensation of key parameters (such as dry ice replenishment and electric field adjustment) reduce operational difficulty and improve production safety. Attached Figure Description

[0019] Figure 1 This is a flowchart of the drying method described in this invention. Detailed Implementation

[0020] The following is in conjunction with the appendix Figure 1 The present invention will be described in detail as follows: A low-temperature drying method for soybean products based on heat exchange technology, the drying method is as follows: Step 1: Pre-processing and plating of soy products Select fresh soy products, remove surface impurities and excess moisture, and cut or shape them according to the type of soy product (such as tofu, dried tofu, and bean curd sticks) to ensure uniform size of individual pieces (error not exceeding 5%). Spread the processed soy products evenly on a high-temperature resistant tray with ventilation holes, and place a silicone heat-conducting pad at the bottom of the tray. The stacking height of the soy products should not exceed 3cm to avoid squeezing between layers and affecting moisture diffusion. In step 1, the pre-treated soy products need to undergo surface spraying. The spray solution is a mixed aqueous solution of 0.5% salt and 0.3% vitamin C, with a spraying volume of 0.1L per 1kg of soy products. After spraying, the product is left to stand for 15 minutes. Through electrolyte adjustment and antioxidant treatment, the stability and flavor retention of the soy products during the drying process are further improved. The diameter of the ventilation holes on the tray is 2mm, the spacing between the holes is 5mm, and they are distributed in a regular hexagonal pattern to ensure that hot nitrogen gas penetrates the material layer evenly. The thickness of the silicone heat-conducting pad is 3mm, and the thermal conductivity is ≥0.8W / (m・K), which enhances the heat transfer efficiency between the tray and the soy products.

[0021] Analysis of the above technical content: This solution mainly adopts a combination design of pretreatment and shaping, spraying with antioxidant liquid, and a breathable tray with a silicone heat-conducting pad. Pretreatment precisely controls the individual size error of the soybean products (≤5%) and stacking height (≤3cm) to avoid interlayer compression hindering moisture diffusion; a spray solution of 0.5% salt and 0.3% vitamin C utilizes electrolytes to regulate protein stability and vitamin C's antioxidant properties to reduce nutrient loss and flavor deterioration during drying; hexagonally distributed ventilation holes (2mm diameter, 5mm spacing) ensure uniform penetration of hot nitrogen gas, and a high thermal conductivity silicone pad (thermal conductivity ≥0.8W / (m・K)) enhances heat transfer efficiency. This solution solves the problems of uneven heating, easy nutrient loss, and poor moisture diffusion in traditional drying methods, achieving uniform pretreatment and quality protection of soybean products before drying, laying the foundation for efficient subsequent drying. The innovation lies in combining electrolyte regulation with antioxidant pretreatment to improve stability during the drying process.

[0022] Step 2: Vacuum Can Pretreatment and Sealing; Place the tray containing the bean products into the stainless steel vacuum can, with the trays layered by the support, maintaining a 15cm gap between layers to ensure smooth airflow inside the can; Close the vacuum can door, start the vacuum pump, reduce the air pressure inside the can to 50-100Pa, maintain for 30 minutes, and remove the air inside the can and residual gas in the gaps between the bean products. In step 2, the vacuum tank adopts a double-layer stainless steel structure, with the inner layer made of 316L stainless steel and the outer layer made of 304 stainless steel. The space between the two layers is filled with polyurethane insulation material (10cm thick, thermal conductivity ≤0.02W / (m・K)). The vacuum pumping device uses two-stage vacuum pumps connected in series. The first stage is a rotary vane vacuum pump, which reduces the air pressure to 1000Pa. The second stage is a diffusion pump, which further reduces the pressure to 50-100Pa. During the pumping process, the air pressure inside the tank is monitored in real time by a vacuum gauge to ensure that the air pressure control accuracy error does not exceed 5Pa.

[0023] Analysis of the above technical content: This solution mainly adopts a double-layer stainless steel vacuum tank (inner layer 316L, outer layer 304) with a polyurethane insulation layer (10cm thick, thermal conductivity ≤0.02W / (m・K)), combined with two-stage vacuum pumps in series (rotary vane pump to 1000Pa, diffusion pump to 50-100Pa). Layered trays (15cm spacing between layers) ensure airflow, and a vacuum gauge monitors the air pressure in real time (error ≤5Pa). The double-layer insulation structure reduces heat exchange between the inside and outside of the tank, maintaining a stable vacuum environment inside; the two-stage extraction system quickly removes residual gas between air and materials, avoiding the impact of oxygen on the quality of bean products. This solution solves the problems of poor insulation, low pressure control accuracy, and poor airflow in traditional vacuum tanks, achieving precise construction of a stable vacuum environment inside the tank. The innovation lies in the combination of double-layer materials and insulation design with two-stage extraction, balancing vacuum level and insulation effect, adapting to the needs of continuous industrial production.

[0024] Step 3: Dry ice surround arrangement and heat exchange system start-up; install a heat insulation sleeve on the outside of the vacuum tank, forming a 5cm wide annular cavity between the insulation sleeve and the outer wall of the vacuum tank, and uniformly fill the cavity with dry ice to ensure full contact between the dry ice and the outer wall of the vacuum tank, maintaining the low temperature environment outside the tank (-20℃ to -15℃); at the same time, start the hot nitrogen supply system inside the tank, heat the nitrogen to 45-50℃ through the nitrogen preheating device, and uniformly introduce it into the vacuum tank through the annular gas distribution pipe inside the tank at a gas flow rate of 0.5-1m³ / h, forming a hot nitrogen convection field in the low temperature environment inside the tank; In step 3, food-grade solid carbon dioxide with a purity of ≥99.9% is used as dry ice. During the filling process, the temperature inside the annular cavity is monitored in real time by a temperature sensor. When the temperature is higher than -15℃, the automatic replenishment device is activated to add dry ice. The nitrogen preheating device uses an electric heating heat exchanger with a heating power of 5kW and is equipped with a temperature feedback control system to ensure that the nitrogen outlet temperature fluctuation does not exceed ±1℃. The annular gas distribution pipe has 1mm diameter gas outlets evenly distributed on it, with the gas outlets facing at a 45° angle to the tray surface to form a spiral airflow and enhance the uniformity of heat exchange.

[0025] Analysis of the above technical content: This solution mainly utilizes a vacuum tank surrounded by dry ice (5cm annular cavity, temperature -20℃ to -15℃) and hot nitrogen convection inside the tank (45-50℃, ventilation rate 0.5-1m³ / h) to construct a highly efficient heat exchange field. Food-grade dry ice (purity ≥99.9%) is automatically replenished to maintain the low temperature, while an electrically heated heat exchanger (5kW) precisely controls the temperature of the nitrogen (fluctuation ±1℃), and an annular gas distribution pipe (1mm outlet, 45° angle) forms a spiral airflow. The temperature difference between the dry ice and hot nitrogen creates efficient heat exchange, the spiral airflow enhances the uniformity of heat transfer, and the automatic ice replenishment and temperature control system ensures environmental stability. This solves the problems of low heat exchange efficiency and uneven temperature distribution in traditional drying methods, achieving highly efficient heat convection in a low-temperature environment of 35-40℃. The innovation lies in combining the low temperature of external dry ice with the internal convection of hot nitrogen, improving the uniformity of heat exchange and reducing energy consumption through airflow guidance design.

[0026] Step 4: Electrode induction treatment and molecular structure optimization; Two sets of platinum electrode plates are symmetrically arranged in a vacuum chamber, with a distance of 8-10 cm between the electrode plates and the surface of the soy products. A high-frequency pulse power supply is turned on to apply a pulsed electric field with a voltage of 5-10 kV and a frequency of 10-20 kHz to the electrode plates. The electrode induction process lasts for 60 minutes, during which the surface potential changes of the soy products are monitored in real time to ensure that the electric field uniformly covers all materials. The electric field improves the internal cross-linking structure of the protein molecules in the soy products, enhances molecular stability, and stimulates the transformation of flavor precursor substances. In step 4, the platinum electrode plate is coated with a titanium nitride coating with a thickness of 5μm to enhance the electrode's corrosion resistance and electric field stability. The high-frequency pulse power supply is equipped with an electric field uniformity detection module, which monitors the electric field strength inside the tank in real time through multiple sampling points to ensure that the electric field strength distribution error does not exceed 10%. During the electrode induction process, the temperature change of the bean product is monitored simultaneously. If the temperature exceeds 40℃, the pulse voltage is automatically reduced by 0.5kV to avoid local overheating from affecting product quality.

[0027] Analysis of the above technical content: This solution mainly uses symmetrically arranged platinum electrode plates (coated with a 5μm titanium nitride coating), applying a pulsed electric field of 5-10kV and 10-20kHz, with an electrode spacing of 8-10cm, and continuously inducing for 60 minutes. An electric field uniformity detection module (error ≤10%) is used in conjunction with temperature control (voltage reduced by 0.5kV above 40℃). The pulsed electric field acts on the protein molecules of soy products, optimizing the cross-linking structure, enhancing stability, and simultaneously stimulating the transformation of flavor precursors; the titanium nitride coating improves the corrosion resistance of the electrodes and the stability of the electric field, and temperature control prevents local overheating. This solves the problems of unstable protein structure, insufficient flavor, and easy local overheating in traditional dried soy products, achieving simultaneous molecular structure optimization and flavor enhancement. The innovation lies in applying electrode induction technology to soy product drying, balancing structural optimization and quality protection through electric field control and temperature linkage.

[0028] Step 5: Dynamic heat exchange drying and parameter control; continuously introduce hot nitrogen and maintain the internal pressure of the tank at 50-100 Pa. Monitor the surface temperature of the soybean products in real time using an internal temperature sensor to ensure the temperature remains stable at 35-40℃; dynamically adjust the nitrogen introduction rate and temperature according to the moisture content of the soybean products. In the initial stage (moisture content 40%-60%), maintain the nitrogen temperature at 45℃ and the aeration rate at 1 m³ / h; in the middle stage (moisture content 20%-40%), adjust to a nitrogen temperature of 42℃ and an aeration rate of 0.8 m³ / h; in the final stage (moisture content 10%-20%), adjust to a nitrogen temperature of 40℃ and an aeration rate of 0.5 m³ / h; replenish dry ice to the annular cavity in real time using a dry ice replenishment device to maintain a stable low-temperature environment outside the tank. In step 5, the moisture content of the soy products is detected in real time by a microwave moisture sensor installed on the top of the vacuum tank. The sensor performs multi-point detection on the soy products on each tray every 10 minutes (5 points are detected on each tray). The detection data is transmitted to the central control system, which automatically generates a moisture content change curve and then dynamically adjusts the nitrogen parameters. The hot nitrogen circulation system is equipped with a high-efficiency heat exchanger to recover the waste heat of the nitrogen discharged during the drying process and use it to preheat the newly introduced nitrogen. The waste heat recovery rate is ≥60%, reducing energy consumption.

[0029] Analysis of the above technical content: This solution mainly adopts a method based on dynamic control of nitrogen parameters according to moisture content (initial 45℃ / 1m³ / h, intermediate 42℃ / 0.8m³ / h, final 40℃ / 0.5m³ / h), microwave moisture sensors detect moisture at multiple points every 10 minutes (5 points per tray), a central control system generates curves and automatically adjusts, and hot nitrogen waste heat is recovered (recovery rate ≥60%). Drying parameters are adjusted in stages according to changes in moisture content to precisely match the moisture evaporation rate; waste heat recovery reduces energy consumption, and real-time monitoring ensures parameter adaptability. This solves the problems of traditional static drying, such as inability to adapt to changes in moisture content, high energy consumption, and uneven drying, achieving dynamic and precise control and energy saving in the drying process. The innovation lies in establishing a dynamic linkage mechanism between moisture content and nitrogen parameters, combined with a waste heat recovery system, to optimize both efficiency and energy consumption.

[0030] Step 6: Humidity Monitoring and Condensation Drainage; Activate the in-tank condensation recovery system, which condenses the moisture evaporated from the hot nitrogen into liquid water through the condensation coils built into the tank wall. The temperature of the condensation coils is controlled between 0-5℃, and the condensate flows into the storage tank through the collection pipe. Monitor the humidity of the nitrogen in the tank in real time using a humidity sensor. When the humidity exceeds 30%, activate the nitrogen purification device to dehumidify and filter the circulating nitrogen before re-introducing it into the tank, ensuring that the humidity of the drying environment is stable between 10%-30%. In step 6, the condenser coil is made of copper-nickel alloy and is spirally distributed on the inner wall of the vacuum tank, with a total heat exchange area of ​​≥2m². The condensate collection pipe is made of stainless steel and equipped with a filter (filtration accuracy 1μm) to remove trace impurities from the condensate. The nitrogen purification device uses molecular sieve desiccant (model 3A) with a dehumidification efficiency of ≥95% and the purified nitrogen dew point of ≤-40℃ to ensure the low humidity requirements of the drying environment.

[0031] Analysis of the above technical content: This solution mainly uses spiral condenser coils (copper-nickel alloy, heat exchange area ≥2m², temperature 0-5℃) on the tank wall to condense moisture, stainless steel collection pipes (1μm filter) to recover condensate, a molecular sieve dehumidifier (model 3A, dehumidification efficiency ≥95%) to purify nitrogen, and a humidity sensor for real-time monitoring (controlled between 10%-30%). The condenser coils rapidly condense water vapor, the filter removes impurities, the dehumidification system maintains a low humidity environment, and humidity-linked purification ensures stable drying conditions. This solves the problems of poor humidity control, easy moisture residue, and low nitrogen utilization in traditional drying methods, achieving precise control of the drying environment humidity and efficient moisture recovery. The innovation lies in combining condensate drainage with nitrogen dehumidification and purification, ensuring the low humidity stability of the drying environment through humidity-linked regulation, and improving product quality consistency.

[0032] Step 7: Drying Termination and Post-processing; When the moisture content of the soy products drops to 8%-12% (detected by the built-in moisture sensor, with a fluctuation of no more than 0.5% over 15 consecutive minutes), stop the supply of hot nitrogen and the electrode induction device; turn off the vacuum pumping system and slowly introduce dry air into the tank to gradually restore the pressure inside the tank to normal pressure (the restoration rate is 10Pa / min to avoid sudden pressure changes that could damage the structure of the soy products); open the vacuum tank door, remove the soy products, and place them in a constant temperature and humidity environment of 25℃ and 50% relative humidity for 30 minutes to cool, thus completing the drying process.

[0033] In step 7, the moisture sensor uses a capacitive measurement principle with a measurement range of 0-100% and a measurement accuracy of ±0.5%. The sensor probe is in direct contact with the surface of the bean product, and the moisture content is calculated using a multi-point averaging method. During the cooling process, a gradient cooling method is adopted, first cooling at 25℃ for 15 minutes, and then transferring to 20℃ for 15 minutes to avoid cracking of the bean product due to excessive temperature difference. After drying, the bean product needs to undergo quality testing, including indicators such as moisture uniformity (error ≤1%), protein retention rate (≥90%), and hardness (20-30N). Only after passing the tests can it be stored in the warehouse.

[0034] Analysis of the above technical content: This solution mainly uses a capacitive moisture sensor (accuracy ±0.5%) to detect moisture content (8%-12%, fluctuation ≤0.5% / 15 minutes), restores atmospheric pressure at a rate of 10Pa / min, and performs gradient cooling (25℃ for 15 minutes → 20℃ for 15 minutes). Finished product testing (moisture uniformity error ≤1%, protein ≥90%, hardness 20-30N). Slow pressure release avoids material structural damage, gradient cooling prevents cracking, and accurate detection ensures finished product quality. This solution solves the problems of inaccurate drying termination judgment, material damage from excessively rapid pressure release, and easy cracking during cooling in traditional methods. It achieves stable post-processing and quality control of dried materials. The innovation lies in combining accurate moisture content detection, slow pressure release, and gradient cooling, and through strict quality testing standards, ensures the stability and high quality of the finished product, adapting to the quality control requirements of industrial mass production.

[0035] Working Principle: This solution primarily achieves low-temperature, high-efficiency drying of soybean products by constructing a highly efficient heat exchange system and combining a vacuum environment with electrode induction technology. First, the soybean products are pre-treated by shaping and spraying with an antioxidant solution, laying a foundation for uniformity and stability during subsequent drying. Then, they are placed in a vacuum tank, where a two-stage vacuum pump evacuates them to a vacuum environment of 50-100 Pa, expelling air and residual gases from between the materials and lowering the boiling point of water to meet the requirements of low-temperature dehydration. Subsequently, dry ice is filled into the annular cavity outside the vacuum tank to create a low-temperature field of -20℃ to -15℃. Hot nitrogen gas at 45-50℃ is introduced into the tank, creating a highly efficient heat exchange field through the temperature difference between the inside and outside. Combined with the spiral airflow formed by the annular gas distribution pipe, this ensures uniform heat transfer and maintains a stable low-temperature environment of 35-40℃ inside the tank. Simultaneously, a pulsed electric field of 5-10kV and 10-20kHz is applied using symmetrically arranged platinum electrode plates to optimize the cross-linking structure of soybean product protein molecules and stimulate flavor transformation. Throughout the drying process, the moisture content is monitored in real time by a microwave moisture sensor, and the central control system dynamically adjusts the nitrogen temperature and ventilation rate. Combined with the condensation drainage and nitrogen purification system, a low humidity environment of 10%-30% is maintained. Finally, the drying process is completed through slow depressurization, gradient cooling, and quality testing, achieving a balance between efficient dehydration and quality retention.

[0036] The core innovation of this solution lies in proposing an integrated low-temperature drying system that combines "vacuum environment + dry ice-hot nitrogen heat exchange + electrode induction + dynamic parameter control." This system solves the technical problems in existing technologies for drying soybean products, such as "difficulty in balancing nutrient retention and efficiency, poor quality stability, high energy consumption, and insufficient industrial adaptability." Simultaneously, it combines electrode induction technology with low-temperature heat exchange drying for the first time, optimizing the protein molecular structure of soy products through pulsed electric fields, simultaneously achieving nutrient retention, flavor enhancement, and texture stability; it innovatively designs a heat exchange structure with dry ice surrounding the vacuum tank and hot nitrogen spiral convection inside, utilizing temperature difference to enhance heat transfer efficiency, and reducing energy consumption in conjunction with a waste heat recovery system; it establishes a dynamic parameter control mechanism based on changes in moisture content, adjusting nitrogen temperature and ventilation rate in stages through real-time sensor feedback and linkage with the central control system to avoid "dry outside and wet inside"; it adopts a double-layer insulated vacuum tank, a two-stage air extraction system, gradient cooling, and slow pressure relief structure and process design to ensure product quality stability and production safety; it incorporates pretreatment spraying of antioxidant liquid, condensate drainage purification, and precise quality testing into the entire process, forming a complete technology chain from raw material processing to finished product control, achieving the dual goals of large-scale industrial production and high-quality product output.

[0037] Technical Effects of Implementing this Solution: The technical effects of implementing this solution are significant. Firstly, in terms of balancing nutrient retention and drying efficiency, the 35-40℃ low-temperature environment and efficient heat exchange design avoid the damage of heat-sensitive nutrients caused by high temperatures while accelerating moisture evaporation. Protein retention is ≥90%, more than 20% higher than traditional hot air drying. Active substances such as soy isoflavones are also effectively preserved. Simultaneously, drying efficiency is more than 40% higher than conventional low-temperature drying, solving the pain point of traditional technologies struggling to balance efficiency and nutrition. Regarding product quality stability, electrode-induced technology optimizes the protein molecular structure, reducing cracking after drying. Dynamic parameter control and uniform heat exchange design ensure that the moisture content error of soy products is ≤1%, completely avoiding the "dry outside, wet inside" problem. The product has a uniform texture and good elasticity. Flavor precursors are enhanced after being excited by the electric field, and the shelf life is extended by more than 3 months compared to traditionally dried products, significantly improving quality consistency. In terms of energy consumption and industrial adaptability, the waste heat recovery rate of hot nitrogen is ≥60%, and the low-temperature environment of dry ice reduces heat loss. Overall energy consumption is reduced by 35% compared to conventional low-temperature drying. The layered design of the vacuum tank is suitable for a capacity of 8-12 tons / day. The fully automated control of the process requires minimal manual intervention, solving the problems of limited capacity and complex operation of traditional vacuum drying, and meeting the needs of large-scale industrial production. In terms of production safety and ease of operation, the pretreatment spraying of antioxidant liquid, condensate drainage, and nitrogen purification design effectively prevent microbial growth and impurity residue. The pressure recovery rate control and gradient cooling process prevent damage to the structure of soybean products. Real-time monitoring and automatic compensation systems for key parameters reduce operational difficulty and improve production safety. At the same time, the finished product undergoes strict quality testing to ensure that indicators such as moisture uniformity, protein retention rate, and hardness meet the standards, significantly improving the product qualification rate. This provides an efficient, high-quality, and energy-saving solution for the soybean product drying industry.

[0038] The relevant data for this plan is as follows: I. Comparative Experimental Design Fresh dried bean curd from the same batch (initial moisture content 55%, protein content 22%) was selected as the experimental subjects. Four groups of experiments were set up, with each group containing 10 kg of samples. All other conditions were the same, except for the drying method. The experimental results are as follows.

[0039] II. Comparative Experiment Data Statistics Table Experimental group Drying method Protein retention rate (%) Moisture content uniformity error (%) Drying time (h) Energy consumption (kWh) Storage period (months) Hardness (N) 1 Method of the present invention 92.5 0.8 4.5 85 12 25 2 Traditional hot air drying (65℃) 70.2 3.5 3.0 120 6 38 3 Conventional low-temperature drying (45℃) 80.5 2.2 8.0 140 8 32 4 Standard vacuum drying (40℃) 85.3 1.5 6.0 110 9 29 III. Data Validity Explanation Sample consistency: Fresh dried bean curd of the same batch and specifications was selected for the experiment. The error of key indicators such as initial moisture content and protein content was ≤2% to ensure that the basic conditions of the samples were consistent and to eliminate the interference of raw material differences on the experimental results.

[0040] Standardized testing methods: Protein retention rate was determined using the Kjeldahl method; moisture content uniformity was calculated using a multi-point (20 test points per sample group) capacitive measurement method; and hardness was determined using a texture analyzer (5mm probe diameter, 1mm / s test speed). All testing methods comply with food industry standards, and the accuracy of the data is traceable.

[0041] Strict variable control: The experiment only changed the drying method, while other parameters (such as sample stacking height, initial treatment process, storage environment, etc.) remained completely consistent, ensuring that the difference in experimental results was only caused by the different drying methods.

[0042] Parallel experimental verification: Three parallel samples were set up for each experiment, and the experimental data were the average value of the parallel samples with an error of ≤3%, to further ensure the reliability and repeatability of the data.

[0043] Industrialization scenario adaptation: The specifications of experimental equipment (vacuum tank volume, heat exchange system power, etc.) simulate the scale of industrial production, and the data can reflect the effect in actual production, which has practical application reference value.

[0044] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and all such equivalent transformations fall within the protection scope of the present invention.

Claims

1. A method for low-temperature drying of soybean products based on heat exchange technology, characterized in that: The drying method is as follows: Step 1: Pre-treatment and plating of soy products Select fresh soy products, remove surface impurities and excess moisture, and cut or shape them according to the type of soy products to ensure that the individual size is uniform and the error does not exceed 5%. Spread the processed soy products evenly on a high-temperature resistant tray with ventilation holes. Place a silicone heat-conducting pad at the bottom of the tray. The stacking height of the soy products should not exceed 3cm to avoid squeezing between layers and affecting moisture diffusion. Step 2: Vacuum Can Pretreatment and Sealing; Place the tray containing the bean products into the stainless steel vacuum can, with the trays layered by the support, maintaining a 15cm gap between layers to ensure smooth airflow inside the can; Close the vacuum can door, start the vacuum pump, reduce the air pressure inside the can to 50-100Pa, maintain for 30 minutes, and remove the air inside the can and residual gas in the gaps between the bean products. Step 3: Dry ice surround arrangement and heat exchange system start-up; install a heat insulation sleeve on the outside of the vacuum tank, forming a 5cm wide annular cavity between the insulation sleeve and the outer wall of the vacuum tank, and evenly fill the cavity with dry ice to ensure full contact between the dry ice and the outer wall of the vacuum tank, maintaining the low temperature environment outside the tank, normally -20℃ to -15℃; at the same time, start the hot nitrogen supply system inside the tank, heat the nitrogen to 45-50℃ through the nitrogen preheating device, and introduce it into the vacuum tank at a uniform speed through the annular gas distribution pipe inside the tank, with a gas flow rate of 0.5-1m³ / h, forming a hot nitrogen convection field in the low temperature environment inside the tank; Step 4: Electrode induction treatment and molecular structure optimization; Two sets of platinum electrode plates are symmetrically arranged in a vacuum chamber, with a distance of 8-10 cm between the electrode plates and the surface of the bean product. The high-frequency pulse power supply is turned on to apply a pulse electric field with a voltage of 5-10 kV and a frequency of 10-20 kHz to the electrode plates. The electrode induction process lasts for 60 minutes, during which the surface potential changes of soy products are monitored in real time to ensure that the electric field uniformly covers all materials. The electric field improves the internal cross-linking structure of soy protein molecules, enhances molecular stability, and stimulates the conversion of flavor precursor substances. Step 5: Dynamic heat exchange drying and parameter control; Hot nitrogen is continuously introduced and the internal pressure is maintained at 50-100 Pa. The surface temperature of the bean products is monitored in real time by a temperature sensor inside the tank to ensure that the temperature is stable at 35-40℃. The nitrogen introduction rate and temperature are dynamically adjusted according to the changes in the moisture content of the bean products. In the initial stage (moisture content 40%-60%), the nitrogen temperature is maintained at 45℃ and the aeration rate is 1 m³ / h. In the middle stage (moisture content 20%-40%), the nitrogen temperature is adjusted to 42℃ and the aeration rate is 0.8 m³ / h. In the final stage (moisture content 10%-20%), the nitrogen temperature is adjusted to 40℃ and the aeration rate is 0.5 m³ / h. Dry ice is continuously replenished to the annular cavity through a dry ice replenishment device to maintain a stable low temperature environment outside the tank. Step 6: Humidity Monitoring and Condensation Drainage; Activate the in-tank condensation recovery system, which condenses the moisture evaporated from the hot nitrogen into liquid water through the condensation coils built into the tank wall. The temperature of the condensation coils is controlled between 0-5℃, and the condensate flows into the storage tank through the collection pipe. Monitor the humidity of the nitrogen in the tank in real time using a humidity sensor. When the humidity exceeds 30%, activate the nitrogen purification device to dehumidify and filter the circulating nitrogen before re-introducing it into the tank, ensuring that the humidity of the drying environment is stable between 10%-30%. Step 7: Drying Termination and Post-processing; When the moisture content of the soy products drops to 8%-12%, the built-in moisture sensor detects the moisture content. If the value fluctuation does not exceed 0.5% for 15 consecutive minutes, stop the supply of hot nitrogen and the electrode induction device; turn off the vacuum pumping system and slowly introduce dry air into the tank to gradually restore the air pressure inside the tank to normal pressure. The restoration rate is 10 Pa / min to avoid sudden pressure changes that could damage the structure of the soy products; open the vacuum tank door, remove the soy products, and place them in a constant temperature and humidity environment of 25℃ and 50% relative humidity for 30 minutes to cool, thus completing the drying process.

2. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 1, the pre-treated soy products need to undergo surface spraying. The spray solution is a mixed aqueous solution of 0.5% salt and 0.3% vitamin C, with a spraying volume of 0.1L per 1kg of soy products. After spraying, the product is left to stand for 15 minutes. Through electrolyte adjustment and antioxidant treatment, the stability and flavor retention of the soy products during the drying process are further improved. The diameter of the ventilation holes on the tray is 2mm, the spacing between the holes is 5mm, and they are distributed in a regular hexagonal pattern to ensure that hot nitrogen gas penetrates the material layer evenly. The thickness of the silicone heat-conducting pad is 3mm, and the thermal conductivity is ≥0.8W / (m・K), which enhances the heat transfer efficiency between the tray and the soy products.

3. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 2, the vacuum tank adopts a double-layer stainless steel structure, with the inner layer made of 316L stainless steel and the outer layer made of 304 stainless steel. The space between the two layers is filled with polyurethane insulation material with a thickness of 10cm and a thermal conductivity of ≤0.02W / (m・K). The vacuum pumping device uses two-stage vacuum pumps connected in series. The first stage is a rotary vane vacuum pump, which reduces the air pressure to 1000Pa. The second stage is a diffusion pump, which further reduces the pressure to 50-100Pa. During the pumping process, the air pressure inside the tank is monitored in real time by a vacuum gauge to ensure that the air pressure control accuracy error does not exceed 5Pa.

4. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 3, food-grade solid carbon dioxide with a purity of ≥99.9% is used as dry ice. During the filling process, the temperature inside the annular cavity is monitored in real time by a temperature sensor. When the temperature is higher than -15℃, the automatic replenishment device is activated to add dry ice. The nitrogen preheating device uses an electric heating heat exchanger with a heating power of 5kW and is equipped with a temperature feedback control system to ensure that the nitrogen outlet temperature fluctuation does not exceed ±1℃. The annular gas distribution pipe has 1mm diameter gas outlets evenly distributed on it, with the gas outlets facing at a 45° angle to the tray surface to form a spiral airflow and enhance the uniformity of heat exchange.

5. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 4, the platinum electrode plate is coated with a titanium nitride coating with a thickness of 5μm to enhance the electrode's corrosion resistance and electric field stability; the high-frequency pulse power supply is equipped with an electric field uniformity detection module, which monitors the electric field strength inside the tank in real time through multiple sampling points to ensure that the electric field strength distribution error does not exceed 10%; During electrode induction, the temperature change of the soy products is monitored simultaneously. If the temperature exceeds 40℃, the pulse voltage is automatically reduced by 0.5kV to avoid local overheating from affecting product quality.

6. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 5, the moisture content of the soy products is detected in real time by a microwave moisture sensor installed on the top of the vacuum tank. The sensor performs multi-point detection on the soy products on each tray every 10 minutes. The detection data is transmitted to the central control system, which automatically generates a moisture content change curve and then dynamically adjusts the nitrogen parameters. The hot nitrogen circulation system is equipped with a high-efficiency heat exchanger to recover the waste heat of the nitrogen discharged during the drying process and use it to preheat the newly introduced nitrogen. The waste heat recovery rate is ≥60%, reducing energy consumption.

7. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 6, the condenser coil is made of copper-nickel alloy and is spirally distributed on the inner wall of the vacuum tank, with a total heat exchange area of ​​≥2m². The condensate collection pipe is made of stainless steel and equipped with a filter with a filtration accuracy of 1μm to remove trace impurities from the condensate. The nitrogen purification device uses molecular sieve desiccant with a dehumidification efficiency of ≥95%, and the purified nitrogen dew point is ≤-40℃ to ensure the low humidity requirements of the drying environment.

8. The method for low-temperature drying of soybean products based on heat exchange technology according to claim 1, characterized in that: In step 7, the moisture sensor uses a capacitive measurement principle with a measurement range of 0-100% and a measurement accuracy of ±0.5%. The sensor probe is in direct contact with the surface of the bean product, and the moisture content is calculated using a multi-point averaging method. During the cooling process, a gradient cooling method is adopted, first cooling at 25℃ for 15 minutes, and then transferring to 20℃ for 15 minutes to avoid cracking of the bean product due to excessive temperature difference. After drying, the bean product needs to undergo quality testing, including moisture uniformity with an error of ≤1%, protein retention rate ≥90%, and hardness of 20-30. Only after passing the tests can it be stored in the warehouse.

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