Efficient and energy-saving drying method for liquorice based on infrared and heat pump combined drying

Abstract

The invention discloses an efficient and energy-saving liquorice drying method based on infrared and heat pump combined drying, which adopts infrared drying equipment and heat pump drying equipment, and comprises the following steps: putting liquorice root strips with the diameter of 10 + / -2 mm into low-temperature freezing equipment, freezing at low temperature, and cutting into liquorice slices with the thickness of 4 + / -0.5 mm; putting the licorice slices into infrared drying equipment, and starting the infrared drying equipment; taking out the liquorice slices subjected to infrared drying, putting the liquorice slices in a well ventilated environment, and regaining moisture so as to uniformly redistribute moisture in the liquorice; and transferring the licorice slices after moisture regaining into heat pump drying equipment, and carrying out deep drying on the licorice. By optimizing the drying process and parameters, high-efficiency and energy-saving drying capable of ensuring the quality of liquorice is realized, the drying quality is ensured, meanwhile, the energy consumption is reduced, and the quality and market competitiveness of liquorice products are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of drying Chinese medicinal materials, and more specifically, to a highly efficient and energy-saving method for drying liquorice based on combined drying of infrared and heat pumps. Background Art

[0002] As an important Chinese medicinal material, licorice is widely used in medicine, food and other fields. In the processing of licorice, drying is a key link. There are many problems with the traditional licorice drying method. On the one hand, the natural drying method is greatly affected by weather conditions. When the weather is unstable, the drying time is difficult to control, which can easily cause the licorice to be in a wet state for a long time, causing problems such as mildew and reducing the quality of the licorice. In addition, natural drying occupies a large area and has extremely low drying efficiency, which cannot meet the needs of large-scale production. On the other hand, although some conventional hot air drying methods can increase the drying speed to a certain extent, the energy consumption is too high. During the hot air drying process, a large amount of heat is wasted in the environment and fails to fully act on the drying of licorice. At the same time, too high a drying temperature can easily destroy the effective ingredients of licorice, affecting its medicinal value. For example, active ingredients such as glycyrrhizic acid in licorice may decompose at high temperatures, reducing the efficacy of licorice. In addition, existing drying equipment has shortcomings in the precise control of licorice moisture content. For example, it is difficult to dynamically adjust drying parameters according to the real-time changes in licorice moisture content, resulting in uneven drying, some licorice is over-dried, and some is under-dried, which seriously affects the quality consistency of the product.

[0003] When trying to solve these problems, due to the characteristics of licorice itself, such as complex internal moisture distribution and sensitivity to temperature, it is difficult to develop an efficient, energy-saving and quality-guaranteed drying method. Therefore, a new licorice drying method is urgently needed to overcome the above problems. Summary of the invention

[0004] The present invention provides a high-efficiency and energy-saving drying method for licorice based on combined infrared and heat pump drying, which optimizes the drying process and parameters to achieve high-efficiency and energy-saving drying while ensuring the quality of licorice, thereby ensuring the drying quality, reducing energy consumption, and improving the quality and market competitiveness of licorice products.

[0005] In order to achieve these purposes and other advantages according to the present invention, a method for efficiently and energy-saving drying of licorice based on combined drying of infrared and heat pump is provided, which adopts infrared drying equipment and heat pump drying equipment, and the method comprises the following steps: Place licorice root strips with a diameter of 10±2 mm in a low-temperature freezing device and freeze them at a low temperature of -30℃ to -20℃ for 1~2 hours, then cut them into licorice slices with a thickness of 4±0.5 mm, and measure the moisture content of the licorice slices; Put the licorice slices into the infrared drying equipment and start the infrared drying equipment: for licorice slices with an initial moisture content ≥ 60%, the initial temperature of the infrared drying equipment is 65°C, the wind speed is 2.5 m / s, and the infrared power is 700 W; for licorice slices with an initial moisture content of < 60%, the initial temperature of the infrared drying equipment is 60°C, the wind speed is 2.3 m / s, and the infrared power is 650 W; the drying time is controlled at 1.5-3 hours, and the moisture content of the licorice slices is less than 40% when sampling and measuring. If the moisture content of the licorice slices is ≥ 40%, continue drying for 0.5-0.8 hours; Take out the infrared dried licorice slices and place them in a well-ventilated environment to rehydrate for 8 to 12 hours to allow the moisture inside the licorice to be evenly redistributed. The rehydrated licorice slices are transferred to the heat pump drying equipment for deep drying of the licorice. The drying temperature is set to 40~50℃, the relative humidity is 30~40%, the drying time is controlled to 6~8 hours, and the moisture content of the licorice slices is measured to be less than 12%. If the moisture content of the licorice slices is measured to be ≥12%, the heat pump drying equipment is controlled to perform pulse drying, with a cycle of drying for 20~30 minutes each time and pausing for 10~15 minutes to perform the remaining drying process.

[0006] Preferably, the step of subsequently cutting into liquorice slices having a thickness of 4±0.5 mm comprises: Select a disc slicer with speed adjustment function and set the speed of the slicer to 50 rpm.

[0007] Preferably, it also includes: An online near-infrared moisture meter is installed inside the infrared drying equipment. During the drying process, the online near-infrared moisture meter continuously detects the moisture content of the licorice slices and feeds the data back to the control system in real time. Once the moisture content reaches the standard of less than 40%, the control system immediately issues a command to stop the operation of the infrared drying equipment. Among them, the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute. The moisture meter is connected to the control system through a high-speed RS485 communication interface, and the detected moisture content data is transmitted to the control system in real time in the form of a digital signal; in the operation interface of the control system, the moisture content is set to less than 40% as the threshold for drying completion; the control system receives the data transmitted by the moisture meter in real time and performs logical judgment; once it detects that the moisture content of the licorice tablets is less than 40% for three consecutive times, the control system determines that the drying has met the standard; when the control system determines that the drying has met the standard, it immediately sends a stop operation command to the power control module of the infrared drying equipment; the power control module responds quickly, cuts off the heating power supply and fan power supply of the equipment, and stops the infrared drying equipment from working.

[0008] Preferably, the licorice tablets with an initial moisture content of ≥60% further include: When the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute, when the moisture content of the licorice tablets is detected to be 40%≤≤60%, the infrared power of the infrared drying equipment is reduced to 600 W.

[0009] Preferably, it also includes: During the drying process, if the moisture content is detected to decrease by less than 0.5% for 5 consecutive times, the infrared power will be increased by 50W to enhance the drying effect; If the moisture content is detected to decrease by more than 1% for 5 consecutive times, the drying power will be reduced by 50 W to make the moisture content fluctuation range of the drying process ≤±2%; In the whole drying process, the infrared power is increased no more than twice, and the infrared power is decreased no more than twice.

[0010] Preferably, if the moisture content of the licorice tablets is still ≥40% after drying for 0.5 to 0.8 hours, the rehumidification time is further increased by 3 to 4 hours after rehumidification for 8 to 12 hours.

[0011] Preferably, during the remaining drying process, if it is detected for 5 consecutive times that the moisture content decreases by less than 0.5% and the moisture content of the licorice slices is not greater than 15%, the operation of the heat pump drying equipment is stopped.

[0012] Preferably, when deep drying the licorice, the drying temperature is set to 45° C. and the relative humidity is set to 35%.

[0013] Preferably, the remaining drying process continues until the moisture content of the liquorice slices is less than 12% when sampled and measured.

[0014] Preferably, pulse drying comprises: The drying phase is 30 minutes: the first 10 minutes are operated at 30-50% of the designed drying power, and the last 20 minutes are operated at the designed drying power; and The pause period is 15 minutes.

[0015] The present invention has at least the following beneficial effects: First, the present invention mainly includes a freezing pretreatment step, an infrared drying step, a rehumidification step, and a heat pump deep drying step. By optimizing the drying process and parameters, efficient energy saving and quality-guaranteed drying of licorice can be achieved. In the freezing pretreatment step, frozen sections can make the internal structure of licorice loose, which is conducive to subsequent drying. In the infrared drying step, different infrared drying parameters are set according to the initial moisture content, which can improve the drying efficiency and avoid over-drying. In the rehumidification step, the rehumidification step makes the internal moisture of licorice uniform, laying a good foundation for subsequent deep drying. In the heat pump deep drying step, heat pump deep drying combined with pulse drying can not only ensure drying quality, but also reduce energy consumption. The entire process effectively improves the efficiency of licorice drying, ensures drying quality, and at the same time reduces energy consumption, thereby improving the quality and market competitiveness of licorice products.

[0016] Second, the present invention has a mechanism for power regulation based on the initial moisture content and the degree of moisture content decline, which greatly improves the stability and controllability of the drying process, reduces the difference in product quality caused by uneven drying, ensures the drying quality of licorice tablets, and retains their effective ingredients to the greatest extent. By accurately controlling the moisture content fluctuation, the difference in product quality caused by uneven drying is reduced, and the consistency and qualified rate of the product are improved. In addition, the number of power adjustments is limited, the service life of the equipment is extended, the equipment maintenance cost is reduced, and a guarantee is provided for the long-term stable operation of licorice drying production. It is ensured that the licorice tablets retain their effective ingredients to the greatest extent while reaching the qualified moisture content, improve the product quality, and at the same time achieve energy saving and consumption reduction, thereby improving the economy and sustainability of the production process.

[0017] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to examples so that those skilled in the art can implement the invention with reference to the description.

[0019] It should be understood that terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0020] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial channels unless otherwise specified.

[0021] The present invention provides a high-efficiency and energy-saving method for drying liquorice based on combined infrared and heat pump drying, using infrared drying equipment and heat pump drying equipment, and the method comprises the following steps: S1: Place licorice root strips with a diameter of 10±2 mm in a low-temperature freezing device and freeze them at a low temperature of -30℃ to -20℃ for 1~2 hours. Then cut them into licorice slices with a thickness of 4±0.5 mm and take the licorice slices to measure the moisture content.

[0022] Low temperature can freeze the water inside the licorice root into ice crystals. The ice crystals expand in volume during the formation process, which will destroy the licorice cell structure and make the originally tight tissue structure loose. This loose structure is easier to cut during subsequent slicing. After being cut into 4±0.5 mm thick licorice slices, during the subsequent drying process, water can more easily migrate from the inside to the surface, greatly improving the drying efficiency. In addition, freezing treatment can inhibit the growth of microorganisms and the activity of enzymes to a certain extent, reduce the risk of deterioration of licorice before drying, and help maintain the quality of licorice.

[0023] S2: Place the licorice slices into the infrared drying equipment and start the infrared drying equipment: for licorice slices with an initial moisture content ≥ 60%, the initial temperature of the infrared drying equipment is set to 65°C, the wind speed is 2.5 m / s, and the infrared power is 700 W; for licorice slices with an initial moisture content of < 60%, the initial temperature of the infrared drying equipment is set to 60°C, the wind speed is 2.3 m / s, and the infrared power is 650 W; the drying time is controlled at 1.5 to 3 hours, and the moisture content of the licorice slices is measured to be < 40%. If the moisture content of the licorice slices is measured to be ≥ 40%, continue drying for 0.5 to 0.8 hours.

[0024] Put the licorice tablets into the infrared drying equipment and set different parameters according to the difference in initial moisture content. Infrared drying uses the thermal effect of infrared rays. Infrared rays can directly penetrate into the interior of the licorice tablets, intensify the vibration of water molecules inside the licorice tablets, generate internal heat, and thus achieve drying from the inside out. For licorice tablets with an initial moisture content of ≥60%, a higher initial temperature and power are set to quickly evaporate a large amount of water and improve drying efficiency; for licorice tablets with an initial moisture content of <60%, the temperature and power are appropriately reduced to avoid the surface of the licorice tablets from drying too quickly due to excessive temperature, forming a hard shell that hinders further loss of internal moisture, and ensuring the uniformity of drying. The drying time is controlled at 1.5~3 hours, and the moisture content is measured by sampling. When the moisture content is <40%, it meets the standard. If it is ≥40%, continue to dry for 0.5-0.8 hours. This flexible adjustment ensures that different batches of licorice tablets can reach the appropriate degree of drying, avoiding energy waste and quality degradation caused by excessive drying.

[0025] S3: Take out the infrared dried licorice slices and place them in a well-ventilated environment to allow them to rehydrate for 8 to 12 hours to allow the moisture inside the licorice to be evenly redistributed.

[0026] After infrared drying, the moisture on the surface of the licorice tablets decreases rapidly, but there is still a certain amount of moisture inside, and the distribution is uneven. During the rehumidification process, due to the effect of environmental humidity, moisture will diffuse from the environment with higher humidity to the inside of the licorice tablets, and the moisture inside the licorice tablets will also be redistributed. The well-ventilated environment accelerates moisture exchange, making the moisture inside the licorice tablets more uniform, creating good conditions for subsequent heat pump deep drying, avoiding partial over-drying and partial under-drying during deep drying due to uneven moisture distribution, and further improving the drying quality.

[0027] S4: Transfer the rehumidified licorice slices to the heat pump drying equipment for deep drying of the licorice. Set the drying temperature to 40~50℃, the relative humidity to 30~40%, and the drying time to 6~8 hours. Take samples to measure the moisture content of the licorice slices to be less than 12%. If the moisture content of the licorice slices is measured to be ≥12%, control the heat pump drying equipment to perform pulse drying, with each drying for 20~30 minutes and a pause of 10~15 minutes to perform the remaining drying process.

[0028] After rehumidification, the licorice tablets are transferred to the heat pump drying equipment. The heat pump drying uses the reverse Carnot cycle principle to absorb heat from the environment and transfer it to the licorice tablets through the phase change of the refrigerant, realizing an efficient and energy-saving drying process. Appropriate temperature and humidity conditions can ensure the continuous evaporation of water and avoid the damage of high temperature to the effective ingredients of licorice, thus ensuring the medicinal value of licorice. If the moisture content of the dried sample is ≥12%, pulse drying is performed, which allows the licorice tablets to have time to redistribute the internal moisture during the drying process, preventing the surface moisture from evaporating too quickly and the internal moisture from migrating in time, reducing quality problems caused by uneven drying, and at the same time reducing the energy consumption of the equipment during the pause stage, achieving energy-saving effects, and finally reaching the drying standard of moisture content <12%, ensuring the drying quality and storage stability of the licorice tablets.

[0029] The above technical scheme mainly includes freezing pretreatment, infrared drying, rehumidification, and heat pump deep drying. By optimizing the drying process and parameters, efficient energy saving and quality-guaranteed licorice drying can be achieved. Frozen slicing in the freezing pretreatment stage can make the internal structure of licorice loose, which is conducive to subsequent drying. In the infrared drying stage, different infrared drying parameters are set according to the initial moisture content, which can improve the drying efficiency and avoid over-drying. In the rehumidification stage, the rehumidification step makes the internal moisture of licorice uniform, laying a good foundation for subsequent deep drying. In the heat pump deep drying stage, heat pump deep drying combined with pulse drying can not only ensure the drying quality, but also reduce energy consumption. The entire process effectively improves the efficiency of licorice drying, ensures the drying quality, and at the same time reduces energy consumption, thereby improving the quality and market competitiveness of licorice products.

[0030] In another technical solution, the step of cutting into licorice slices having a thickness of 4±0.5 mm in S1 comprises: Select a disc slicer with speed adjustment function and set the speed of the slicer to 50 rpm.

[0031] In the above technical scheme, the licorice root strips are conveyed to the rotating disc blade through the feeding system, and the shear force generated by the high-speed rotation of the blade cuts the licorice root strips, thereby completing the slicing process. Uniform slice thickness is crucial for the subsequent drying process, which can ensure that the water evaporation rate of each piece of licorice is relatively consistent during the drying process, avoiding the situation where some pieces are over-dried and some are under-dried due to thickness differences, thereby improving the stability of the drying quality. Licorice is relatively hard and rich in fiber. If the rotation speed is too fast, at the moment when the blade contacts the licorice root strips, the strong impact force generated by the high speed may cause the edges of the licorice slices to be uneven, tearing, breaking, etc., affecting the integrity and quality of the slices. If the rotation speed is too slow, although the slice quality can be guaranteed to a certain extent, it will greatly reduce the slice efficiency and cannot meet the needs of large-scale production. After a lot of practice and theoretical analysis, a speed of 50 rpm can achieve a good balance between ensuring slice quality and efficiency. At this speed, the cutting process of the blade on the licorice root strips is relatively stable, and the shear force is moderate, which can not only efficiently cut the licorice root strips into uniform slices, but also ensure that the slice edges are neat and complete.

[0032] In another technical solution, it also includes: An online near-infrared moisture meter is installed inside the infrared drying equipment. During the drying process, the online near-infrared moisture meter continuously detects the moisture content of the licorice slices and feeds back the data to the control system in real time. Once the moisture content reaches the standard of less than 40%, the control system immediately issues a command to stop the operation of the infrared drying equipment.

[0033] The online near-infrared moisture meter uses the characteristics of the interaction between near-infrared light and material molecules to detect the moisture content of licorice tablets. This non-contact detection method will not cause physical damage to the licorice tablets, and can obtain moisture content information in real time and quickly.

[0034] Among them, the online near-infrared moisture meter continuously detects the moisture content of licorice tablets at a high frequency. Specifically, the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute. The moisture meter is connected to the control system through a high-speed RS485 communication interface, and the detected moisture content data is transmitted to the control system in real time in the form of a digital signal. It is more stable during the transmission process and is not easily affected by noise, which can ensure the accuracy and integrity of the data. In the operation interface of the control system, based on the licorice drying process requirements, the moisture content is pre-set as the threshold for drying completion of 40%; the control system receives the data transmitted by the moisture meter in real time and performs logical judgment; once it is detected that the moisture content of the licorice tablets is less than 40% for three consecutive times, the control system determines that the drying is up to standard; when the control system determines that the drying is up to standard, it immediately sends a stop operation command to the power control module of the infrared drying equipment; the power control module responds quickly, and cuts off the heating power supply and fan power supply of the equipment through electrical components such as relays, so that the infrared drying equipment stops working. Cutting off the heating power stops the generation of infrared radiation, and cutting off the fan power stops the flow of air, so that the infrared drying equipment stops working immediately, accurately controls the drying process, and avoids over-drying.

[0035] In the above technical solution, the moisture content of licorice slices is monitored in real time and accurately during the drying process, which changes the traditional method of relying on manual timed sampling and detection, and greatly improves the frequency and accuracy of detection. This enables operators to grasp the drying process at any time and adjust the drying parameters in time. Through the automated control system, the equipment can be automatically stopped when the moisture content reaches the preset standard, which reduces manual intervention, reduces labor intensity, and improves production efficiency. The loss of active ingredients and the decline in product quality caused by over-drying are reduced. Accurate drying control also helps to improve energy utilization efficiency, reduce energy consumption, and provide strong support for the sustainable development of licorice drying production.

[0036] In another technical solution, the licorice tablets with an initial moisture content ≥ 60% further include: When the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute, when the moisture content of the licorice tablets is detected to be 40%≤≤60%, the infrared power of the infrared drying equipment is reduced to 600 W.

[0037] In the above technical solution, this regulation is based on the physical principle of water evaporation. Licorice tablets with an initial moisture content of ≥60% have a high moisture content in the early stage of drying. Drying with a higher infrared power (700 W) can quickly evaporate a large amount of water and improve drying efficiency. As the drying process progresses, the moisture content decreases, and the rate at which the moisture inside the licorice tablets migrates to the surface slows down. If the high power is still maintained at this time, the moisture on the surface of the licorice tablets will evaporate rapidly, forming a hard shell, which will hinder the further diffusion of the internal moisture, resulting in uneven drying, and may damage the quality of the licorice tablets due to local overheating. Reducing the power to 600 W can make the infrared radiation intensity moderate, allowing moisture to migrate from the inside to the surface and evaporate at a more reasonable rate, ensuring the uniformity and quality of drying. This method of dynamically adjusting the power according to the moisture content range effectively avoids drying defects caused by excessive power.

[0038] In another technical solution, it also includes: During the drying process, if the moisture content was detected to decrease by less than 0.5% for five consecutive times, it indicated that the drying rate was too slow. In this case, the infrared power was increased by 50 W to enhance the drying effect.

[0039] The slow drop in moisture content may be due to insufficient infrared radiation energy, which cannot effectively cause the internal moisture of the licorice tablets to evaporate and migrate to the surface. Increasing the power can increase the intensity of infrared radiation, provide more energy for moisture evaporation, and speed up the drying process.

[0040] If the moisture content is detected to decrease by more than 1% for 5 consecutive times, it indicates that the drying rate is too fast, which may cause local overheating of the licorice tablets and damage to their quality. In this case, the drying power will be reduced by 50 W to make the moisture content fluctuation range of the drying process ≤±2%, making the drying process more stable. Among them, during the entire drying process, in order to ensure system stability and equipment reliability, the infrared power is increased no more than twice, and the infrared power is reduced no more than twice, to avoid damage to the equipment due to frequent adjustments.

[0041] In the above technical solution, the power regulation mechanism based on the decrease in moisture content greatly improves the stability and controllability of the drying process. It avoids a series of problems caused by too fast or too slow drying rates, ensures the drying quality of licorice tablets, and retains their effective ingredients to the greatest extent. By accurately controlling the fluctuation of moisture content, the difference in product quality caused by uneven drying is reduced, and the consistency and qualified rate of products are improved. In addition, limiting the number of power adjustments prolongs the service life of the equipment, reduces the equipment maintenance cost, and provides a guarantee for the long-term stable operation of licorice drying production.

[0042] In another technical solution, if the moisture content of the licorice tablets is still measured to be ≥40% after drying for 0.5 to 0.8 hours, the rehumidification time is further increased by 3 to 4 hours after rehumidification for 8 to 12 hours.

[0043] In the above technical scheme, after the prescribed infrared drying time, even after continuing to dry for 0.5~0.8 hours, the moisture content of the licorice tablets is still ≥40%, which indicates that under the current drying conditions, the internal moisture migration of the licorice tablets is blocked and it is difficult to achieve the expected degree of drying. At this time, the rehumidification stage is entered. The conventional rehumidification time is 8~12 hours, and the rehumidification time is further increased by 3~4 hours on this basis. During the rehumidification process, the licorice tablets are in an environment with high relative humidity, and water molecules will diffuse from the environment to the inside of the licorice tablets. Prolonging the rehumidification time can allow more water to enter the inside of the licorice tablets, making the internal moisture distribution more uniform. This is based on the diffusion principle of water molecules. Driven by the concentration difference, moisture migrates from the high concentration area (environment) to the low concentration area (inside the licorice tablets). After sufficient rehumidification, the internal structure of the licorice tablets is restored to a certain extent, creating more favorable conditions for possible subsequent re-drying, so that moisture can migrate more smoothly from the inside to the surface in subsequent drying.

[0044] In another technical solution, during the remaining drying process, if the moisture content is detected to decrease by less than 0.5% for 5 consecutive times, and the moisture content of the licorice tablets is not more than 15%, the heat pump drying equipment is stopped. A small decrease in moisture content indicates that the drying rate has slowed down, and a moisture content of no more than 15% is close to the target moisture content (<12%). Continuing to dry may lead to over-drying, resulting in energy waste, and may also damage the quality of the licorice tablets, such as degrading their active ingredients. Stopping the equipment at this time is based on a comprehensive consideration of the drying process and product quality, avoiding unnecessary energy consumption and product quality risks. This method of stopping drying based on dual indicators accurately controls the drying end point. It not only prevents the product from being unqualified due to stopping drying before the target moisture content is reached, but also avoids the adverse effects of over-drying on product quality and energy. It ensures that the licorice tablets retain their active ingredients to the greatest extent while reaching the qualified moisture content, improves product quality, and achieves energy saving and consumption reduction, thereby improving the economy and sustainability of the production process.

[0045] In another technical solution, when deep drying licorice, the drying temperature is set at 45°C, which can provide sufficient energy to promote the evaporation of water inside the licorice tablets, while not destroying the effective ingredients of the licorice due to excessively high temperature. The relative humidity of 35% creates an environment suitable for water evaporation, which will neither inhibit water evaporation due to excessive humidity nor cause excessive drying due to low humidity, thus affecting product quality. Under this temperature and humidity condition, the rate at which water migrates from the inside of the licorice tablets to the surface and evaporates reaches a relatively ideal equilibrium state, which is conducive to achieving efficient and high-quality drying.

[0046] In another technical solution, the remaining drying process continues until the moisture content of the licorice tablets is less than 12%. During the entire drying process, the moisture content is tested by regular sampling to monitor the drying progress in real time. As long as the moisture content does not reach the standard of less than 12%, drying will continue. This continuous monitoring and adjustment process ensures that the licorice tablets can eventually meet the qualified moisture content requirements and meet the product quality standards.

[0047] In another technical solution, pulse drying includes: The drying stage is 30 minutes: the first 10 minutes are operated at 30-50% of the designed drying power, which is a relatively low power operation. This allows the surface temperature of the licorice tablets to rise slowly, and the moisture to gradually evaporate, to avoid the instantaneous evaporation of large amounts of surface moisture due to excessive power, which would form a hard shell and hinder the migration of internal moisture. The next 20 minutes are operated at the designed drying power to accelerate moisture evaporation and improve drying efficiency. The pause stage is 15 minutes, during which the equipment stops heating, but the moisture inside the licorice tablets continues to diffuse and redistribute.

[0048] In the drying energy consumption comparison test, the grouping is shown in Table 1. Different drying treatments are performed on the licorice raw materials in each group to achieve a target moisture content of licorice tablets of <12%. The treatment results are shown in Table 2. The hardness (N) is measured using a hardness tester, and the glycyrrhizic acid retention rate (%) is determined using high performance liquid chromatography.

[0049] Table 1 Table 2 As can be seen from Table 2, in the total energy consumption data, the energy consumption of Example 1 seems to be high, mainly due to the energy consumption accumulation of multiple links and specific processes. However, it performs better in ensuring the drying quality of licorice, such as the retention rate of the active ingredient glycyrrhizic acid and the hardness of the texture. From the perspective of the comprehensive benefits of the product, it is reasonable.

[0050] As can be seen from Table 2, in the hardness data, Example 1 is better than Comparative Examples 1-6. The freezing pretreatment freezes the internal water of the licorice root strips into ice crystals, and the expansion of the ice crystals destroys the cell structure, making the tissue structure loose, and the subsequent slicing more uniform, laying the foundation for good texture. During infrared drying and heat pump deep drying, the water is evenly lost, and there is no deformation of the internal structure due to too fast or too slow drying. Pulse drying plays a buffering role in the heat pump deep drying link, allowing the licorice tablets to have time to redistribute the internal water, avoiding the texture being too hard or too soft, and ensuring that the licorice tablets have a good balance of brittleness and toughness. Comparative Example 1 has no freezing pretreatment, the licorice texture itself is hard and rich in fiber, and it may not be uniform when slicing. The water loss is uneven during the drying process, which easily leads to hardening of the texture, affecting the taste and subsequent processing. Comparative Example 2 does not undergo infrared drying to initially remove water and regain moisture to make the water evenly distributed. Direct heat pump drying will cause the internal water migration of the licorice tablets to be chaotic, some areas are dried too fast, and some are too slow, resulting in uneven texture and overall hardness. In the first half of infrared drying, the moisture in Comparative Example 3 gradually evaporated as expected, and the structure of the licorice tablets gradually stabilized. However, as the drying time increased, excessive drying damaged the internal fiber structure of the licorice tablets, and because the bound water could not be further removed by deep drying with a heat pump, the licorice tablets still retained a lot of moisture, resulting in the inability to form a tight structure, showing a soft texture, which was not conducive to storage and transportation. In Comparative Example 4, the drying effects of licorice tablets with different moisture contents were inconsistent, resulting in uneven texture, some of which were over-dried and hard, and some of which were insufficiently dried and soft. In Comparative Example 5, there was no buffering of pulse drying, and a large amount of moisture was lost in a short period of time. The internal structure of the licorice tablets shrank rapidly, resulting in a hard texture. However, compared with Comparative Examples 1 and 2, the texture was relatively uniform due to freezing pretreatment and reasonable pre-drying links. In Comparative Example 6, the constant power resulted in different drying effects of licorice tablets with different moisture contents, inconsistent water loss rates, and uneven texture and overall hardness.

[0051] As can be seen from Table 2, in the glycyrrhizic acid retention rate data, Example 1 is better than Comparative Examples 1-6. In the freezing pretreatment link, low temperature can inhibit the growth of microorganisms and the activity of enzymes, reducing the possibility of glycyrrhizic acid being decomposed before drying. The infrared drying link can quickly evaporate water and avoid the damage of glycyrrhizic acid by high temperature by dynamically adjusting the temperature and power according to the initial moisture content. The rehumidification link redistributes the internal moisture of licorice evenly, creating good conditions for heat pump deep drying. Heat pump deep drying is carried out at suitable temperature and humidity, and pulse drying prevents the surface moisture from evaporating too quickly, reduces local overheating caused by obstruction of internal moisture migration, and further protects effective ingredients such as glycyrrhizic acid. Due to the lack of freezing pretreatment in Comparative Example 1, microorganisms and enzymes may have begun to decompose glycyrrhizic acid before drying. In the subsequent drying process, there is no structural optimization brought by the freezing link, and moisture migration is relatively difficult, which may cause local overheating and increase the risk of glycyrrhizic acid decomposition. Comparative Example 2 directly enters the heat pump drying, lacking infrared drying and rehumidification links. Without infrared drying to quickly reduce the moisture content, the heat pump drying time will be extended, and due to the uneven distribution of moisture in the early stage, local overheating is prone to occur during the drying process, resulting in a large amount of decomposition of glycyrrhizic acid. Although Comparative Example 3 has frozen pretreatment and infrared drying, although the infrared drying can quickly evaporate moisture in the initial stage, as the drying time is extended, the continued heat effect may still cause some heat-sensitive glycyrrhizic acid to decompose. In addition, there is a lack of heat pump deep drying, and it is in a state of high moisture content for a long time. Microorganisms and enzymes still have certain activity and may continue to decompose glycyrrhizic acid. In the infrared drying link of Comparative Example 4, the initial moisture content setting parameters are not distinguished. Some licorice slices with high moisture content may not be dried enough, and some licorice slices with low moisture content may be over-dried. The over-dried part of the glycyrrhizic acid is easy to decompose, and the overall retention rate is affected. Comparative Example 5 lacks pulse drying. During the heat pump deep drying, the surface moisture evaporates quickly, and the internal moisture migration is not smooth, which is easy to cause local overheating, causing the glycyrrhizic acid to decompose. Compared with the present application method, the retention rate will be reduced. In comparative example 6, the power of the infrared drying link is constant and cannot be adjusted according to the drying process, which easily leads to uneven drying, resulting in partial decomposition of glycyrrhizic acid and a decrease in the overall retention rate.

[0052] The number of devices and processing scales described here are used to simplify the description of the present invention. Applications, modifications and variations of the present invention will be obvious to those skilled in the art.

[0053] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the examples shown and described herein.

Claims

1. An efficient and energy-saving drying method for licorice based on combined infrared and heat pump drying, using infrared drying equipment and heat pump drying equipment, characterized in that: The method comprises the following steps: Place licorice root strips with a diameter of 10±2 mm in a low-temperature freezing device and freeze them at a low temperature of -30℃ to -20℃ for 1~2 hours, then cut them into licorice slices with a thickness of 4±0.5 mm, and measure the moisture content of the licorice slices; Put the licorice slices into the infrared drying equipment and start the infrared drying equipment: for licorice slices with an initial moisture content ≥ 60%, the initial temperature of the infrared drying equipment is 65°C, the wind speed is 2.5 m / s, and the infrared power is 700 W; for licorice slices with an initial moisture content of < 60%, the initial temperature of the infrared drying equipment is 60°C, the wind speed is 2.3 m / s, and the infrared power is 650 W; the drying time is controlled at 1.5-3 hours, and the moisture content of the licorice slices is less than 40% when sampling and measuring. If the moisture content of the licorice slices is ≥ 40%, continue drying for 0.5-0.8 hours; Take out the infrared dried licorice slices and place them in a well-ventilated environment to rehydrate for 8 to 12 hours to allow the moisture inside the licorice to be evenly redistributed. The rehydrated licorice slices are transferred to the heat pump drying equipment for deep drying of the licorice. The drying temperature is set to 40~50℃, the relative humidity is 30~40%, the drying time is controlled to 6~8 hours, and the moisture content of the licorice slices is measured to be less than 12%. If the moisture content of the licorice slices is measured to be ≥12%, the heat pump drying equipment is controlled to perform pulse drying, with a cycle of drying for 20~30 minutes each time and pausing for 10~15 minutes to perform the remaining drying process.

2. The efficient and energy-saving drying method for liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: The steps of cutting into 4±0.5 mm thick licorice slices include: Select a disc slicer with speed adjustment function and set the speed of the slicer to 50 rpm.

3. The efficient and energy-saving drying method for liquorice based on combined infrared and heat pump drying according to claim 2, characterized in that: Also includes: An online near-infrared moisture meter is installed inside the infrared drying equipment; During the drying process, the online near-infrared moisture meter continuously detects the moisture content of the licorice tablets and feeds the data back to the control system in real time; once the moisture content reaches the standard of less than 40%, the control system immediately issues a command to stop the operation of the infrared drying equipment; Among them, the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute. The moisture meter is connected to the control system through a high-speed RS485 communication interface, and the detected moisture content data is transmitted to the control system in real time in the form of a digital signal; in the operation interface of the control system, the moisture content is set to less than 40% as the threshold for drying completion; the control system receives the data transmitted by the moisture meter in real time and performs logical judgment; once it detects that the moisture content of the licorice tablets is less than 40% for three consecutive times, the control system determines that the drying has met the standard; when the control system determines that the drying has met the standard, it immediately sends a stop operation command to the power control module of the infrared drying equipment; the power control module responds quickly, cuts off the heating power supply and fan power supply of the equipment, and stops the infrared drying equipment from working.

4. The efficient and energy-saving drying method for liquorice based on combined infrared and heat pump drying according to claim 3, characterized in that: Licorice tablets with an initial moisture content ≥60% also include: When the online near-infrared moisture meter detects the moisture content of licorice tablets at a frequency of once per minute, when the moisture content of the licorice tablets is detected to be 40%≤≤60%, the infrared power of the infrared drying equipment is reduced to 600 W.

5. The efficient and energy-saving drying method for liquorice based on combined infrared and heat pump drying according to claim 3, characterized in that: Also includes: During the drying process, if the moisture content was detected to decrease by less than 0.5% for five consecutive times, the infrared power was increased by 50 W to enhance the drying effect; If the moisture content is detected to decrease by more than 1% for 5 consecutive times, the drying power will be reduced by 50 W to make the moisture content fluctuation range of the drying process ≤±2%; In the whole drying process, the infrared power is increased no more than twice, and the infrared power is decreased no more than twice.

6. The efficient and energy-saving method for drying liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: If after drying for 0.5 to 0.8 hours, the moisture content of the licorice tablets is still measured to be ≥ 40%, then after 8 to 12 hours of rehumidification, continue to increase the rehumidification time by 3 to 4 hours.

7. The method for efficiently and energy-saving drying of liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: During the remaining drying process, if the moisture content is detected to decrease by less than 0.5% for 5 consecutive times and the moisture content of the licorice slices is not greater than 15%, the heat pump drying equipment is stopped.

8. The efficient and energy-saving method for drying liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: When deep drying licorice, set the drying temperature to 45°C and the relative humidity to 35%.

9. The method for efficiently and energy-saving drying of liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: The remaining drying process continues until the moisture content of the licorice tablets is less than 12%.

10. The method for efficiently and energy-saving drying of liquorice based on combined infrared and heat pump drying according to claim 1, characterized in that: Pulse drying includes: The drying phase is 30 minutes: the first 10 minutes are operated at 30-50% of the designed drying power, and the last 20 minutes are operated at the designed drying power; and The pause period is 15 minutes.

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