A tobacco leaf curing method based on curing barn air volume adjustment

Abstract

The application discloses a tobacco curing method based on flue air volume adjustment, which is characterized by the following aspects: the hot air inlet and the return air inlet are transformed into flaps, the frequency conversion technology is adopted for the bidirectional circulating fan, the air volume before 42 DEG C of the dry ball temperature in the yellowing period and the dry muscle period is reduced, the return air volume before 42 DEG C and in the dry muscle period is increased, the return air volume after 42 DEG C and in the color fixing period is reduced, the automatic adjustment of the air inlet volume and the return air volume in the curing process is realized, the forced dehumidification of the flue in the large dehumidification stage is strengthened, the loss of air heat energy and tobacco aroma substances in the curing process is reduced, the risk of burnt tobacco leaves in the curing process is reduced, the uniformity and consistency of the tobacco leaves in the whole flue are realized, the consistency of the cured tobacco leaves is improved, and the aroma quality of the cured tobacco leaves is improved.

Description

Technical Field

[0001] This invention relates to a method for curing tobacco leaves based on the air volume regulation of the curing barn, belonging to the field of tobacco curing technology. Background Technology

[0002] Currently, intensive curing barns achieve dehumidification and tobacco leaf drying through forced ventilation. Forced ventilation uses a circulating fan to force hot air into the barn through the hot air inlet of the loading chamber, then dehumidifies through dehumidification louvers, and finally retains moisture and reduces heat loss through the return air vent. Existing intensive curing barns are mainly of two types: rising airflow and falling airflow. The hot air inlet size is 2700mm × 400mm, and the return air vent size is 1400mm × 400mm. Currently, both types of intensive curing barns have significant temperature differences between the upper and lower layers during curing, especially in four-layer loading barns. This is detrimental to improving the changes in tobacco leaves during curing and the uniformity and consistency of the initial curing raw materials, easily leading to significant differences in the internal and external quality of the cured tobacco leaves. Furthermore, although these two types of intensive curing barns can reduce curing losses, industry feedback indicates that the cured tobacco leaves from intensive curing barns currently have less aroma than those from conventionally ventilated curing barns. In addition, these two types of dense curing barns cannot achieve forced dehumidification for tobacco leaves of different parts, moisture content and curing barn loads, which leads to certain risks in the curing process.

[0003] Based on the above, patent document (publication number CN113261694A) discloses a dense tobacco curing barn with a reversible circulating fan. The barn includes a loading chamber and a heating chamber, with a partition between them. Air vents are located at the top and bottom of the partition. Dehumidification windows are provided on both the top and bottom sides of the barn. A fan reversing mechanism is located in the heating chamber, and the heating components are positioned below the fan reversing mechanism. Patent document (publication number CN109820225A) discloses a method for controlling the circulating fan in a dense curing barn to reduce the loss of aroma substances in tobacco leaves. During the yellowing stage, from ignition to the dry-bulb temperature reaching 40°C, the forward rotation time is 50 minutes, and the reverse rotation time is 10 minutes. During the color-fixing stage, the reverse rotation function is turned off, and the fan continues to rotate forward. During the drying stage, after the dry-bulb temperature reaches 57°C, the forward and reverse rotation functions are restarted, with a forward rotation time of 50 minutes and a reverse rotation time of 10 minutes, until curing is complete. By rotating the circulating fan in both directions, the changes in the tobacco leaves during the curing process and the uniformity and consistency of the initial-cured tobacco leaves are ensured.

[0004] Patent document (publication number CN201045862Y) discloses a tobacco curing barn with controllable return air, which adjusts the return air volume by installing a return air door at the return air inlet connecting the loading chamber and the heating chamber. Patent document (publication number CN215270533U) discloses an automatic return air control device for a tobacco curing barn, including a frame located at the return air inlet / return air duct of the curing barn, a rotating shaft running through both sides of the frame, a flap fixedly connected to the rotating shaft inside the frame, a motor fixedly connected to one end of the rotating shaft on one side of the frame, a dry temperature sensor located inside the loading chamber, and an electrical control box located on the outer wall of the curing barn, which is electrically connected to the motor and the dry temperature sensor respectively. Patent document (publication number CN214229820U) discloses a high-intensity curing barn circulating return air control system in the field of tobacco production and processing technology. The system includes a curing barn wall, an air distribution plate, a mounting shaft, an adjusting handle, and an indicator panel. An air inlet is provided on the curing barn wall. The size of the air distribution plate matches the size of the air inlet. The air distribution plate is located inside the air inlet and is fixedly connected to the mounting shaft. An indicator panel is loosely fitted on the mounting shaft and fixed to the right side of the curing barn wall. Two connecting blocks are provided at the right end of the mounting shaft, with a gap between them. The bottom of the adjusting handle is hinged between the two connecting blocks by a pin. The indicator panel also has a scale and an adjusting groove. The width of the adjusting groove matches the width of the adjusting handle. Patent document (publication number CN204812000U) discloses a controllable tobacco curing barn. A first fan is located near the air inlet at the lower part of the hot air chamber, and a second fan blowing upwards is located opposite the first fan at the lower part of the curing chamber. The tobacco hanging rack includes vertically arranged vertical rods and horizontally arranged horizontal rods, with multiple locking parts on the vertical rods to engage with the horizontal rods. The controllable tobacco curing barn also includes a motor located at the lower part of each vertical rod and a transmission rod connected to the motor, with the upper part of the transmission rod connected to the bottom of the vertical rod. An air inlet gate and an air return gate are respectively provided at the air inlet and return air inlet. During tobacco curing and non-curing processes, the tobacco curing chamber and the hot air chamber can be spatially independent or connected. Patent document (publication number CN201947926U) discloses a novel air duct system for tobacco curing, including a curing chamber with a drying zone for drying and dehumidifying the tobacco. At the bottom of the curing chamber, within the drying zone, multiple sets of air circulation devices are installed to dehumidify and heat the air in the drying zone using an external heat source, and to circulate the air after tobacco curing. These air circulation devices can also, based on humidity sensor readings within the curing chamber, mix the air returned from the drying zone with outside air in an appropriate proportion, dehumidify and heat it again, and then release it. At the top of the curing chamber, within the drying zone, multiple sets of return air circulation devices are installed to return the air from the drying zone to the air circulation devices. These return air circulation devices can also control the exhaust of the air from the drying zone outside the curing chamber based on the humidity level within the drying zone. The air circulation devices are connected to the return air circulation devices via pipelines.

[0005] While the above-mentioned methods can regulate the intake and exhaust air volumes during the curing process, there is still room for improvement in the aroma quality of the tobacco leaves. How to integrate air volume regulation into the curing process to enhance the aroma quality of the cured tobacco leaves remains to be studied. Furthermore, currently there are no corresponding control techniques for tobacco leaves of different parts, moisture contents, and the amount of tobacco loaded in the curing barn, which may lead to untimely dehumidification and damage to the tobacco leaves during curing. Summary of the Invention

[0006] Based on the above, the present invention provides a method for curing tobacco leaves based on the air volume regulation of the curing barn. By embedding air volume regulation into the curing process, the aroma quality of the cured tobacco leaves can be effectively improved.

[0007] The technical solution of this invention is: a method for curing tobacco leaves based on the air volume regulation of the curing barn, comprising:

[0008] S1, Intensive Baking Chamber Renovation: The circulating fan in the heating chamber is a bidirectional axial flow circulating fan. The hot air inlet and return air outlet are designed to be the same size. Automatically rotating flaps are installed in the inlet and return air outlet. Two dehumidification louvers are opened at the bottom and top of the two opposite walls of the smoke loading chamber connected by the heat insulation wall. Baffles are installed on the outside of the dehumidification louvers. When the airflow direction is upward, the baffles are controlled to close the dehumidification louvers at the bottom. When the airflow direction is downward, the baffles are controlled to close the dehumidification louvers at the top.

[0009] S2, Yellowing Stage: Before ignition, rotate the hot air inlet and return air vent flaps to 90 degrees, close the dehumidification louvers, and circulate the air in both directions for 1-2 hours. After ignition, raise the dry bulb temperature to 32-34°C and the wet bulb temperature to 32-33°C at a rate of 1°C / h. Rotate the hot air inlet and return air vent flaps to 60-80 degrees and maintain the temperature for 2-3 hours to initiate the yellowing process. Then, raise the dry bulb temperature to 35-36°C and the wet bulb temperature to 34-35°C at a rate of 1°C / h. Rotate the hot air inlet and return air vent flaps to 60-80 degrees and maintain the temperature for 4-6 hours until the upper and lower layers of tobacco leaves are 10-20% yellow. Afterward, maintain the temperature at a rate of 1°C / h... Raise the dry-bulb temperature to 38–40°C and the wet-bulb temperature to 36–37°C. Rotate the hot air inlet flap at 50–70 degrees and the return air inlet flap at 40–60 degrees. Maintain this temperature for 20–30 hours until the upper and lower layers of tobacco leaves turn 70–80% yellow and the middle layer turns 60–70% yellow, becoming soft. Then, raise the dry-bulb temperature to 42°C at a rate of 1°C / 2–3 hours, maintaining the wet-bulb temperature at 35–37°C. Rotate the hot air inlet flap at 90 degrees and the return air inlet flap at 30–50 degrees. Maintain this temperature for 18–25 hours until the upper and lower layers of tobacco leaves turn yellow with green veins, are fully wilted and soft, and have curled tips and edges. The reversal interval of the circulating fan should be 0.5 hours.

[0010] S3, Color Fixing Period: Raise the dry-bulb temperature to 44℃ at a rate of 1℃ / 2-3h, maintaining a wet-bulb temperature of 35-37℃. The hot air inlet flap should rotate at 90 degrees, and the return air inlet flap at 30-50 degrees. Maintain this temperature for 10-15h, removing any remaining green residue from the leaves until at least 1 / 3 of the tobacco leaves in both layers are dry. Afterward, raise the dry-bulb temperature to 47-48℃ at a rate of 1℃ / 2h, maintaining a wet-bulb temperature of 38-39℃. The hot air inlet flap should rotate at 90 degrees. The return air inlet flap rotates at an angle of 40–60 degrees, and the temperature is maintained for 10–15 hours until the tobacco leaves in the entire kiln turn yellow, the leaves are semi-dry, and they form small rolls. Afterward, the dry bulb temperature is raised to 53–54°C and the wet bulb temperature to 39–40°C at a rate of 1°C / 2 hours. The hot air inlet flap rotates at an angle of 90 degrees, and the return air inlet flap rotates at an angle of 50–70 degrees. The temperature is maintained for 20–25 hours until the tobacco leaves in the entire kiln are completely dry and form large rolls. The time interval between the forward and reverse rotation of the circulating fan is 1 hour.

[0011] S4, Drying Stage: Raise the dry bulb temperature to 59-60℃ at a rate of 1℃ / h, and stabilize the wet bulb temperature at 40-41℃. The hot air inlet flap rotates at 70-90 degrees, and the return air inlet flap rotates at 60-80 degrees. Maintain this temperature for 6-10 hours until more than 2 / 3 of the main stems of the tobacco leaves in both the upper and lower layers are dry. Raise the dry bulb temperature to 65-68℃ at a rate of 1℃ / h, and stabilize the wet bulb temperature at 41-42℃. The hot air inlet flap rotates at 60-80 degrees, and the return air inlet flap rotates at 60-80 degrees. Maintain this temperature for 20-30 hours until all the tobacco leaves in the kiln are completely dry. The time interval between forward and reverse rotation of the circulating fan is 1.5 hours. For densely packed curing barns with four layers of tobacco, the wet bulb temperature during the drying stage should not exceed 41.5℃.

[0012] Preferably, the length and width of both the hot air inlet and the return air outlet are 2700mm × 400mm.

[0013] Preferably, in steps S2 to S4, for standard dense drying barns with a smoke load greater than 360 rods, the dry bulb temperature is 38–40°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air vent flap is 30–40 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air vent flap is 30–40 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 50–60 degrees.

[0014] Preferably, in steps S2 to S4, for standard dense drying barns with a smoke load of less than 360 rods, the dry bulb temperature is 38–40°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 60–70 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 60–70 degrees.

[0015] Preferably, in steps S2 to S4, for fresh tobacco leaves with a moisture content greater than 85%, the rotation angle of the return air inlet flap is 40 to 50 degrees when the dry bulb temperature is 38 to 40°C; 30 to 40 degrees when the dry bulb temperature is 42°C; 30 to 40 degrees when the dry bulb temperature is 44°C; 40 to 50 degrees when the dry bulb temperature is 47 to 48°C; 50 to 60 degrees when the dry bulb temperature is 53 to 54°C; and 50 to 60 degrees when the dry bulb temperature is 53 to 54°C.

[0016] Preferably, in steps S2 to S4, for fresh tobacco leaves with a moisture content of less than 85%, the rotation angle of the return air inlet flap is 50 to 60 degrees when the dry bulb temperature is 38 to 40°C; 40 to 50 degrees when the dry bulb temperature is 42°C; 40 to 50 degrees when the dry bulb temperature is 44°C; 50 to 60 degrees when the dry bulb temperature is 47 to 48°C; 60 to 70 degrees when the dry bulb temperature is 53 to 54°C; and 60 to 70 degrees when the dry bulb temperature is 53 to 54°C.

[0017] Preferably, in steps S2 to S4, for the lower fresh tobacco leaves, the dry bulb temperature is 38–40°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 50–60 degrees.

[0018] Preferably, in steps S2 to S4, for the upper and middle fresh tobacco leaves, the dry bulb temperature is 38–40°C, and the rotation angle of the return air inlet flap is 50–60 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air inlet flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 60–70 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 60–70 degrees.

[0019] Preferably, in steps S2 to S4, the bidirectional axial flow circulating fan adopts frequency conversion technology, with a frequency of 20 to 30 Hz before 38°C and after 60°C, a frequency of 30 to 40 Hz from the start of stable temperature baking at 38°C to 42°C, a frequency of 40 to 50 Hz from the start of stable temperature baking at 42°C to the end of stable temperature baking at 60°C.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention transforms a unidirectional circulating fan into a bidirectional circulating fan, and modifies the hot air inlet, return air inlet, dehumidification louver device and its operation, to achieve bidirectional circulation of hot airflow in the curing barn, reducing the temperature and humidity difference between different curing stages, improving the uniformity and consistency of tobacco leaf changes during curing, shortening the curing time, and improving the appearance quality and uniformity of the cured tobacco leaves. It effectively solves the problems of uneven yellowing of tobacco leaves and large temperature difference between upper and lower layers in the existing unidirectional airflow movement mode of curing barns.

[0022] 2. This invention, by modifying the hot air inlet and return air outlet to flaps and adopting variable frequency technology for the bidirectional circulating fan, reduces the air intake volume before the dry bulb temperature reaches 42℃ during the yellowing stage and during the drying stage, increases the return air volume before 42℃ and during the drying stage, and reduces the return air volume after 42℃ and during the color-fixing stage. This achieves automatic adjustment of the air intake and return air volume in the curing barn during the curing process, strengthens the forced dehumidification during the large dehumidification stage of the curing barn, reduces the loss of air heat energy and tobacco aroma substances during the curing process, reduces the risk of damaging tobacco leaves during the curing process, achieves uniformity and consistency of tobacco leaf changes throughout the curing barn, improves the consistency of the raw tobacco leaves after curing, and improves the aroma quality of the cured tobacco leaves.

[0023] 3. Based on the differences in the part of the fresh tobacco leaf, the moisture content of the fresh tobacco leaf, and the amount of tobacco loaded in the curing barn, this invention sets the parameter for the rotation angle of the return air vent flap during the curing process. This highlights the curing barn's moisture retention and forced dehumidification functions, reduces the risk of tobacco leaf curing, and effectively solves the problems of mismatch between the air intake and return air volume of existing curing barns and the curing process, as well as the problem of damaged tobacco leaves. Attached image description:

[0024] Figure 1 A schematic diagram showing the view of the insulation wall from inside the smoke loading chamber;

[0025] Figure 2 A schematic diagram showing the view of the insulation wall from outside the heating room;

[0026] Attached diagram labels: 1. Insulation wall, 2. Air inlet, 3. Return air inlet, 4. Flip panel, 5. Motor, 6. Dehumidification louver, 7. Baffle, 8. Electric push rod. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] refer to Figure 1 and Figure 2 The renovation of the intensive drying oven involves several modifications: The heating chamber's circulating fan is now a bidirectional axial flow fan with a frequency of 20-50Hz. The hot air inlet, originally 2700mm x 400mm, is now a lightweight, corrosion-resistant metal flap. Each flap has a rotating shaft at one end, connected to a temperature and humidity controller. The flap can rotate from 0 to 90 degrees. The return air vent, previously 1400mm x 400mm, is now 2700mm x 400mm. This new return air vent is also a lightweight, corrosion-resistant metal flap with rotating shafts at both ends. Each shaft has a motor connected to a temperature and humidity controller. The flap can rotate from 0 to 90 degrees. When the flap is at 90 degrees, both the inlet and return air vents are fully open; when it is at 0 degrees, both are closed. Two 400mm x 400mm desiccant louvers are installed at the bottom and top of the two opposite walls of the tobacco loading chamber connected to the insulation wall of the curing barn. A sliding baffle is installed on the outside of the desiccant louvers, connected to an electric push rod. The electric push rod moves the baffle, which is connected to a temperature and humidity controller for temperature and humidity regulation. When the airflow direction is upward, the motor controls the baffle to move and close the bottom desiccant louver; when the airflow direction is downward, the motor controls the baffle to move and close the top desiccant louver. To ensure the reliability of the baffle movement, guide rails are installed on both sides of the desiccant louvers, and the sides of the baffle are slidably mounted on the guide rails.

[0029] The experimental results of this invention are verified below:

[0030] I. Comparative Analysis with Local Standard Intensive Drying Barns and Conventional Three-Stage Drying Process

[0031] The experiment was conducted in Fuquan City, Guizhou Province, from 2021 to 2022. The tested flue-cured tobacco variety was Yunyan 87, and the 11th and 12th leaves from the middle section were used as experimental materials. The tested tobacco leaves were cultivated and managed according to the local standardized practices for high-quality tobacco production, and harvested at maturity according to the tobacco leaf maturity standards. A comparative experiment was conducted using a standard intensive curing barn and a conventional three-stage curing process as controls, and a modified airflow dual-circulation intensive curing barn and the tested curing method as comparative treatments. Except for the curing barn structure and curing process conditions, all other factors, such as tobacco variety, quantity, and packing density, were the same.

[0032] (1) Baking process of the present invention

[0033] S1, tobacco loading, dense curing barn with three layers of tobacco loading, the amount of tobacco loaded is 350 sticks, the average moisture content of the tobacco leaves is 82%, and the tobacco leaves are from the middle part;

[0034] S2, Yellowing Stage: Before ignition, the hot air inlet and return air outlet flaps are rotated to 90 degrees, the dehumidification louvers are closed, and the circulating fan circulates in both directions for 1 hour each. After ignition, the dry bulb temperature is raised to 33°C and the wet bulb temperature to 32°C at a rate of 1°C / h. The hot air inlet and return air outlet flaps are rotated to 80 degrees, and the temperature is maintained for 2 hours to initiate the yellowing process of the tobacco leaves. Afterward, the dry bulb temperature is raised to 36°C and the wet bulb temperature to 35°C at a rate of 1°C / h. The hot air inlet and return air outlet flaps are rotated to 70 degrees, and the temperature is maintained for 5 hours until the upper and lower layers of tobacco leaves have turned 20% yellow. Afterward, the temperature is maintained at 1°C / h... The dry-bulb temperature was raised to 39℃, and the wet-bulb temperature to 36.5℃. The hot air inlet flap rotated at 70 degrees, and the return air flap rotated at 60 degrees. The leaves were baked at this stable temperature for 25 hours until the top and bottom layers of tobacco leaves turned 70% yellow and the middle layer turned 60-70% yellow, and the leaves softened. Then, the dry-bulb temperature was raised to 42℃ at a rate of 1℃ / 3 hours, and the wet-bulb temperature to 36℃. The hot air inlet flap rotated at 90 degrees, and the return air flap rotated at 50 degrees. The leaves were baked at this stable temperature for 20 hours until the top and bottom layers of tobacco leaves turned yellow with green veins, were fully wilted and softened, and had curled tips and edges. The time interval between the forward and reverse rotation of the circulating fan was 0.5 hours.

[0035] S3, Color Fixing Period: Raise the dry-bulb temperature to 44℃ and the wet-bulb temperature to 36℃ at a rate of 1℃ / 3h, with the hot air inlet flap rotating at 90 degrees and the return air inlet flap rotating at 50 degrees. Maintain this temperature for 12h, removing any remaining green on the leaves until more than 1 / 3 of the tobacco leaves in both layers are dry. Then, raise the dry-bulb temperature to 48℃ and the wet-bulb temperature to 39℃ at a rate of 1℃ / 2h, with the hot air inlet flap rotating at 90 degrees and the return air inlet flap rotating at 50 degrees. Maintain this temperature for 15h, until the tobacco veins of the entire batch turn yellow, the leaves are semi-dry, and the leaves are rolled into small rolls. Then, raise the dry-bulb temperature to 54℃ and the wet-bulb temperature to 39℃ at a rate of 1℃ / 2h, with the hot air inlet flap rotating at 90 degrees and the return air inlet flap rotating at 60 degrees. Maintain this temperature for 20h, until the tobacco leaves of the entire batch are completely dry and rolled into large rolls. The time interval between the forward and reverse rotation of the circulating fan is 1h.

[0036] S4, Drying stage: Increase the dry bulb temperature to 60℃ at a rate of 1℃ / h, stabilize the wet bulb temperature at 40℃, rotate the hot air inlet flap at 80 degrees and the return air inlet flap at 70 degrees, and bake at a stable temperature for 8 hours until the main stems of the upper and lower layers of tobacco leaves are more than 2 / 3 dry; Increase the dry bulb temperature to 68℃ at a rate of 1℃ / h, stabilize the wet bulb temperature at 41℃, rotate the hot air inlet flap at 70 degrees and the return air inlet flap at 60 degrees, and bake at a stable temperature for 25 hours until all the tobacco leaves in the kiln are completely dry; the time interval between forward and reverse rotation of the circulating fan is 1.5 hours.

[0037] Preferably, in steps S2 to S4, the bidirectional axial flow circulating fan adopts frequency conversion technology, with a frequency of 25Hz before 38℃ and after 60℃, a frequency of 35Hz from the start of stable temperature baking at 38℃ to 42℃, a frequency of 45Hz from the start of stable temperature baking at 48℃ to the end of stable temperature baking at 60℃, and a frequency of 45Hz from the start of stable temperature baking at 42℃ to 48℃.

[0038] (2) Conventional three-stage baking process

[0039] The local curing process follows the conventional three-stage curing process for flue-cured tobacco varieties (GB / T 23219—2008). As before, the dense curing barn is filled with three layers of tobacco, with a total load of 350 tobacco leaves. The average moisture content of the tobacco leaves is 82%, and the leaves are from the middle section.

[0040] Yellowing stage: After loading the tobacco, raise the temperature of the curing barn to 35℃ with a low flame, maintaining a wet-bulb temperature of 34℃. Once the leaf tips turn yellow, increase the dry-bulb temperature to 38℃ at a rate of 1℃ every 2 hours, and maintain this temperature for an extended period, controlling the wet-bulb temperature at 36℃. This will ensure that about 80% of the tobacco leaves in the curing barn, measured by the thermometer, reach 70% to 80% yellowing, while simultaneously softening the leaves (with a water loss of about 30%). Then, raise the temperature to 42℃, maintaining a wet-bulb temperature of 37℃ for an extended period, until the tobacco leaves are yellow with slightly green veins, wilting and collapsing, and the midrib softens.

[0041] Color fixation period: The dry-bulb temperature is first increased at an average rate of 1°C every 3 hours to 46°C and then kept stable for an extended period, causing the tobacco leaves to turn yellow and lose moisture to reach the small rolling stage. Then, the temperature is increased at a rate of 1°C every 2 hours to 54°C and kept stable for 10 hours to achieve leaf dryness. As the dry-bulb temperature rises, the wet-bulb temperature gradually rises and stabilizes at 39°C.

[0042] Drying stage: Increase the temperature from 54℃ to 68℃ at a rate of 1℃ per hour and maintain it until the tobacco leaves are completely dry. Before the dry bulb temperature reaches 60℃, maintain the wet bulb temperature at 41℃; after reaching 60℃, gradually close the inlet and outlet vents, reduce the ventilation volume, and maintain the wet bulb temperature at 42℃.

[0043] The following evaluation and analysis compares the tobacco leaves cured in this invention—including the uniformity of tobacco leaf changes during the curing process, the quality of the cured tobacco leaves, and the economic characteristics—with those cured in a standard airflow-rising intensive curing barn and a conventional three-stage curing process.

[0044] 1. The effect of different treatments on the softening, wilting, and yellowing of tobacco leaves during the curing process.

[0045] Table 1. Effects of different treatments on the softening, wilting, and yellowing of tobacco leaves during the curing process.

[0046]

[0047]

[0048] Two samples of tobacco leaves (two poles' distance from the loading chamber door) were taken from the bottom and top racks during the curing process. The degree of yellowing, softening of the leaves, and softening of the midrib were measured and statistically analyzed. The results are shown in Table 1. Table 1 shows that, compared with the standard intensive curing barn with rising airflow and the conventional three-stage curing process, the curing method of this invention can improve the uniformity of softening, wilting, yellowing, and dehydration of tobacco leaves in different racks during the curing process, which is beneficial to improving the appearance quality of the cured tobacco leaves.

[0049] 2. Effects of different treatments on the appearance quality of flue-cured tobacco leaves

[0050] Table 2. Effects of different treatments on the appearance quality of cured tobacco leaves

[0051]

[0052] As shown in Table 2, compared with the control, the appearance quality of the tobacco leaves after curing by the method of the present invention is better overall, especially in terms of tobacco leaf appearance color, oil content and chroma.

[0053] 3. Effects of different treatments on the grade and economic traits of cured tobacco leaves

[0054] Table 3. Effects of different treatments on the grade and economic traits of cured tobacco leaves.

[0055]

[0056] As shown in Table 3, compared with the control, the tobacco leaves roasted by the method of the present invention have a higher proportion of orange-yellow tobacco, a higher proportion of medium-grade tobacco, and a higher average price.

[0057] 4. Effects of different treatments on the content of aroma components in flue-cured tobacco leaves

[0058] Table 4. Effects of different treatments on the content of aroma components in cured tobacco leaves (μg / g)

[0059]

[0060] As shown in Table 4, compared with the control, the roasting method of the present invention has higher contents of aroma substances such as carotenoid degradation products, chlorophyll degradation product neophytediene, and Maillard browning reaction products in tobacco leaves after roasting.

[0061] 5. Effects of different treatments on the style characteristics, sensory quality, and industrial usability of cured tobacco leaves

[0062] Table 5. Effects of different treatments on the flavor characteristics, sensory quality, and industrial usability of cured tobacco leaves.

[0063]

[0064] (1) Each individual indicator has a maximum score of 9 points. The higher the intensity concentration, the higher the score. For other indicators, the better the quality characteristics, the higher the score. (2) Intensity and intensity are style characteristics and are not included in the calculation of the total score.

[0065] (3) Total sensory quality score = (aroma quality × 0.3 + aroma quantity × 0.3 + off-odors × 0.08 + irritation × 0.15 + aftertaste × 0.17) × 11.1.

[0066] As shown in Table 4, compared with the control, the roasting method of the present invention has higher scores in the evaluation of the style characteristics and sensory quality of the roasted tobacco leaves, and better industrial usability and formulation adaptability.

[0067] II. Comparative Analysis with Alternating Airflow Baking Process

[0068] The experiment was conducted in Suiyang County, Zunyi City, Guizhou Province from 2021 to 2022. The tested flue-cured tobacco variety was Yunyan 87, and the 11th and 12th leaves from the middle section were used as experimental materials. The tested tobacco leaves were cultivated and managed according to the local standardized production practices for high-quality tobacco leaves, and harvested at maturity according to the tobacco leaf maturity standards. A comparative experiment was conducted using an alternating airflow dense curing barn (without modifications to the air inlet and outlet) and a three-stage curing process as controls, and a modified dual-circulation airflow dense curing barn (with modified air inlet and outlet) and the tested curing method as comparative treatments. Except for air volume and curing barn structure conditions, all other factors, such as tobacco variety, quantity, and packing density, were kept the same.

[0069] (1) Baking process of the present invention

[0070] S1, tobacco loading, dense curing barn with three layers of tobacco loading, the amount of tobacco loaded is 380 sticks, the average moisture content of the tobacco leaves is 83%, and the tobacco leaves are from the middle part;

[0071] S2, Yellowing Stage: Before ignition, the hot air inlet and return air outlet flaps are rotated to 90 degrees, the dehumidification louvers are closed, and the circulating fan circulates in both directions for 1.5 hours each. After ignition, the dry bulb temperature is raised to 32°C at a rate of 1°C / h, the wet bulb temperature is 32°C, the hot air inlet and return air outlet flaps are rotated to 60 degrees, and the temperature is maintained for 3 hours to initiate the yellowing process of the tobacco leaves. Afterward, the dry bulb temperature is raised to 36°C at a rate of 1°C / h, the wet bulb temperature is 35°C, the hot air inlet and return air outlet flaps are rotated to 60 degrees, and the temperature is maintained for 5 hours until the upper and lower layers of tobacco leaves have turned 20% yellow. Afterward, the temperature is raised to 1°C / h... The dry-bulb temperature is raised to 38℃ and the wet-bulb temperature to 36.5℃. The hot air inlet flap rotates at 70 degrees and the return air inlet flap rotates at 50 degrees. The temperature is maintained for 30 hours until the top and bottom layers of tobacco leaves turn 70% yellow and the middle layer turns 60% yellow, and the leaves become soft. Then, the dry-bulb temperature is raised to 42℃ and the wet-bulb temperature to 36℃ at a rate of 1℃ / 3 hours. The hot air inlet flap rotates at 90 degrees and the return air inlet flap rotates at 40 degrees. The temperature is maintained for 20 hours until the top and bottom layers of tobacco leaves turn yellow with green veins, are fully wilted and soft, and have curled tips and edges. The time interval between the forward and reverse rotation of the circulating fan is 0.5 hours.

[0072] S3, Color Fixing Period: Raise the dry-bulb temperature to 44℃ and the wet-bulb temperature to 37℃ at a rate of 1℃ / 3h, with the hot air inlet flap rotating at 90 degrees and the return air flap rotating at 35 degrees. Maintain this temperature for 12h, removing any remaining green on the leaves until more than 1 / 3 of the tobacco leaves in both layers are dry. Then, raise the dry-bulb temperature to 48℃ and the wet-bulb temperature to 38℃ at a rate of 1℃ / 2h, with the hot air inlet flap rotating at 90 degrees and the return air flap rotating at 45 degrees. Maintain this temperature for 15h, until the tobacco veins of the entire batch turn yellow, the leaves are semi-dry, and the leaves are rolled into small coils. Then, raise the dry-bulb temperature to 54℃ and the wet-bulb temperature to 39℃ at a rate of 1℃ / 2h, with the hot air inlet flap rotating at 90 degrees and the return air flap rotating at 60 degrees. Maintain this temperature for 20h, until the tobacco leaves of the entire batch are completely dry and rolled into large coils. The time interval between the forward and reverse rotation of the circulating fan is 1h.

[0073] S4, Drying stage: Increase the dry bulb temperature to 59℃ at a rate of 1℃ / h, stabilize the wet bulb temperature at 40℃, rotate the hot air inlet flap at 80 degrees and the return air inlet flap at 70 degrees, and bake at a stable temperature for 8 hours until the main stems of the upper and lower layers of tobacco leaves are more than 2 / 3 dry; Increase the dry bulb temperature to 67℃ at a rate of 1℃ / h, stabilize the wet bulb temperature at 41℃, rotate the hot air inlet flap at 70 degrees and the return air inlet flap at 65 degrees, and bake at a stable temperature for 25 hours until all the tobacco leaves in the kiln are completely dry; the time interval between forward and reverse rotation of the circulating fan is 1.5 hours.

[0074] Preferably, in steps S2 to S4, the bidirectional axial flow circulating fan adopts frequency conversion technology, with a frequency of 28Hz before 38℃ and after 60℃, a frequency of 40Hz from the start of stable temperature baking at 38℃ to 42℃, from the start of stable temperature baking at 48℃ to the end of stable temperature baking at 60℃, and a frequency of 48Hz from the start of stable temperature baking at 42℃ to 48℃.

[0075] (2) Conventional three-stage baking process

[0076] The local curing process follows the conventional three-stage curing process for flue-cured tobacco varieties (GB / T 23219—2008). As before, the dense curing barn is filled with tobacco in three layers, with a total load of 380 tobacco leaves. The average moisture content of the tobacco leaves is 83%, and the leaves are from the middle section.

[0077] Yellowing stage: After loading the tobacco, raise the temperature of the curing barn to 35℃ with a low flame, maintaining a wet-bulb temperature of 34℃. Once the leaf tips turn yellow, increase the dry-bulb temperature to 38℃ at a rate of 1℃ every 2 hours, and maintain this temperature for an extended period, controlling the wet-bulb temperature at 36℃. This will ensure that about 80% of the tobacco leaves in the curing barn, measured by the thermometer, reach 70% to 80% yellowing, while simultaneously softening the leaves (with a water loss of about 30%). Then, raise the temperature to 42℃, maintaining a wet-bulb temperature of 37℃ for an extended period, until the tobacco leaves are yellow with slightly green veins, wilting and collapsing, and the midrib softens.

[0078] Color fixation period: The dry-bulb temperature is first increased at an average rate of 1°C every 3 hours to 46°C and then kept stable for an extended period, causing the tobacco leaves to turn yellow and lose moisture to reach the small rolling stage. Then, the temperature is increased at a rate of 1°C every 2 hours to 54°C and kept stable for 10 hours to achieve leaf dryness. As the dry-bulb temperature rises, the wet-bulb temperature gradually rises and stabilizes at 39°C.

[0079] Drying stage: Increase the temperature from 54℃ to 68℃ at a rate of 1℃ per hour and maintain it until the tobacco leaves are completely dry. Before the dry bulb temperature reaches 60℃, maintain the wet bulb temperature at 41℃; after reaching 60℃, gradually close the inlet and outlet vents, reduce the ventilation volume, and maintain the wet bulb temperature at 42℃.

[0080] The control group consisted of an alternating airflow dense curing barn (without modification of the air inlet and return vent) and a three-stage curing process. The treatment group consisted of a modified dual-circulation airflow dense curing barn (with modification of the air inlet and return vent) and this curing method. The following evaluation and analysis will be conducted on the content of aroma components in the cured tobacco leaves, the style characteristics of the cured tobacco leaves, the sensory quality, and the industrial usability.

[0081] 1. Effects of different treatments on the content of aroma components in flue-cured tobacco leaves

[0082] Table 6. Effects of different treatments on the content of aroma components in cured tobacco leaves (μg / g)

[0083]

[0084] As shown in Table 6, compared with the control, the roasting method of the present invention has higher content of aroma substances such as carotenoid degradation products, chlorophyll degradation product neophytediene, and Maillard browning reaction products in tobacco leaves after roasting.

[0085] 2. Effects of different treatments on the style characteristics, sensory quality, and industrial usability of flue-cured tobacco leaves

[0086] Table 7. Effects of different treatments on the flavor characteristics, sensory quality, and industrial usability of cured tobacco leaves.

[0087]

[0088] (1) Each individual indicator has a maximum score of 9 points. The higher the intensity concentration, the higher the score. For other indicators, the better the quality characteristics, the higher the score. (2) Intensity and intensity are style characteristics and are not included in the calculation of the total score.

[0089] (3) Total sensory quality score = (aroma quality × 0.3 + aroma quantity × 0.3 + off-odors × 0.08 + irritation × 0.15 + aftertaste × 0.17) × 11.1.

[0090] As shown in Table 7, compared with the control, the roasting method of the present invention has higher scores in the evaluation of the style characteristics and sensory quality of the roasted tobacco leaves, and better industrial usability and formulation adaptability.

[0091] III. Optimization Experiment of Return Air Volume Parameters in Intensive Drying Barrel

[0092] The experiment was conducted in Fuquan City and Zunyi City, Guizhou Province from 2020 to 2022. The tested flue-cured tobacco variety was Yunyan 87, and the 11th to 12th leaves from the middle part of the plant were used as experimental materials. The tested tobacco leaves were cultivated and managed according to the local standardized production standards for high-quality tobacco leaves, and were harvested at maturity according to the tobacco leaf maturity standards. Based on the modified airflow dual-circulation intensive curing barn, comparative curing experiments were carried out on tobacco leaves with different loading amounts, moisture contents, and parts of the plant. The following is an example of the experimental setup for different loading amounts. The experiment set up three loading amount treatments (320, 360, and 400 stems) and two curing process treatments, as shown in Table 8. Except for the differences in loading amount and return air volume in the curing process, all other factors, such as the curing barn structure and tobacco variety, were the same.

[0093] Table 8. Effects of different treatments on the economic traits, total score of style characteristics, total score of sensory quality evaluation, and industrial usability of cured tobacco leaves.

[0094]

[0095] Baking Process 1 Key Parameter Settings and Operations: Dry bulb temperature 38~40℃, return air vent flap rotation angle 40~50 degrees; Dry bulb temperature 42℃, return air vent flap rotation angle 30~40 degrees; Dry bulb temperature 44℃, return air vent flap rotation angle 30~40 degrees; Dry bulb temperature 47~48℃, return air vent flap rotation angle 40~50 degrees; Dry bulb temperature 53~54℃, return air vent flap rotation angle 50~60 degrees; Dry bulb temperature 53~54℃, return air vent flap rotation angle 50~60 degrees.

[0096] Baking Process 2 Key Parameter Settings and Operations: Dry bulb temperature 38-40℃, return air vent flap rotation angle 50-60 degrees; Dry bulb temperature 42℃, return air vent flap rotation angle 40-50 degrees; Dry bulb temperature 44℃, return air vent flap rotation angle 40-50 degrees; Dry bulb temperature 47-48℃, return air vent flap rotation angle 50-60 degrees; Dry bulb temperature 53-54℃, return air vent flap rotation angle 60-70 degrees; Dry bulb temperature 53-54℃, return air vent flap rotation angle 60-70 degrees.

[0097] Table 8 shows that different tobacco loading treatments were used to evaluate the economic traits, total score of style characteristics, total score of sensory quality, and industrial usability of the cured tobacco leaves. The results indicate that with a tobacco loading of 320 sticks, curing process 2 resulted in better economic traits, total score of style characteristics, total score of sensory quality, and industrial usability of the cured tobacco leaves. With a tobacco loading of 360 sticks, there were no significant differences in these indicators among the different curing processes. With a tobacco loading of 400 sticks, curing process 1 resulted in better economic traits, total score of style characteristics, total score of sensory quality, and industrial usability of the cured tobacco leaves.

[0098] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for curing tobacco leaves based on the air volume regulation of the curing barn, characterized in that, include: S1, Intensive Baking Chamber Renovation: The circulating fan in the heating chamber is a bidirectional axial flow circulating fan. The hot air inlet and return air outlet are designed to be the same size. Automatically rotating flaps are installed in the inlet and return air outlet. Two dehumidification louvers are opened at the bottom and top of the two opposite walls of the smoke loading chamber connected by the heat insulation wall. Baffles are installed on the outside of the dehumidification louvers. When the airflow direction is upward, the baffles are controlled to close the dehumidification louvers at the bottom. When the airflow direction is downward, the baffles are controlled to close the dehumidification louvers at the top. S2, Yellowing Stage: Before ignition, rotate the hot air inlet and return air vent flaps to 90 degrees, close the dehumidification louvers, and circulate the air in both directions for 1-2 hours. After ignition, raise the dry bulb temperature to 32-34°C and the wet bulb temperature to 32-33°C at a rate of 1°C / h. Rotate the hot air inlet and return air vent flaps to 60-80 degrees and maintain the temperature for 2-3 hours to initiate the yellowing process. Then, raise the dry bulb temperature to 35-36°C and the wet bulb temperature to 34-35°C at a rate of 1°C / h. Rotate the hot air inlet and return air vent flaps to 60-80 degrees and maintain the temperature for 4-6 hours until the upper and lower layers of tobacco leaves are 10-20% yellow. Afterward, maintain the temperature at a rate of 1°C / h... Raise the dry-bulb temperature to 38–40°C and the wet-bulb temperature to 36–37°C. Rotate the hot air inlet flap at 50–70 degrees and the return air inlet flap at 40–60 degrees. Maintain this temperature for 20–30 hours until the upper and lower layers of tobacco leaves turn 70–80% yellow and the middle layer turns 60–70% yellow, becoming soft. Then, raise the dry-bulb temperature to 42°C at a rate of 1°C / 2–3 hours, maintaining the wet-bulb temperature at 35–37°C. Rotate the hot air inlet flap at 90 degrees and the return air inlet flap at 30–50 degrees. Maintain this temperature for 18–25 hours until the upper and lower layers of tobacco leaves turn yellow with green veins, are fully wilted and soft, and have curled tips and edges. The reversal interval of the circulating fan should be 0.5 hours. S3, Color Fixing Period: Raise the dry-bulb temperature to 44℃ at a rate of 1℃ / 2-3h, maintaining a wet-bulb temperature of 35-37℃. The hot air inlet flap should rotate at 90 degrees, and the return air inlet flap at 30-50 degrees. Maintain this temperature for 10-15h, removing any remaining green residue from the leaves until at least 1 / 3 of the tobacco leaves in both layers are dry. Afterward, raise the dry-bulb temperature to 47-48℃ at a rate of 1℃ / 2h, maintaining a wet-bulb temperature of 38-39℃. The hot air inlet flap should rotate at 90 degrees. The return air inlet flap rotates at an angle of 40–60 degrees, and the temperature is maintained for 10–15 hours until the tobacco leaves in the entire kiln turn yellow, the leaves are semi-dry, and they form small rolls. Afterward, the dry bulb temperature is raised to 53–54°C and the wet bulb temperature to 39–40°C at a rate of 1°C / 2 hours. The hot air inlet flap rotates at an angle of 90 degrees, and the return air inlet flap rotates at an angle of 50–70 degrees. The temperature is maintained for 20–25 hours until the tobacco leaves in the entire kiln are completely dry and form large rolls. The time interval between the forward and reverse rotation of the circulating fan is 1 hour. S4, Drying stage: Increase the dry bulb temperature to 59-60℃ at a rate of 1℃ / h, and stabilize the wet bulb temperature at 40-41℃. The hot air inlet flap rotates at 70-90 degrees, and the return air inlet flap rotates at 60-80 degrees. Maintain this temperature for 6-10 hours until more than 2 / 3 of the main stems of the tobacco leaves in both the upper and lower layers are dry. Increase the dry bulb temperature to 65-68℃ at a rate of 1℃ / h, and stabilize the wet bulb temperature at 41-42℃. The hot air inlet flap rotates at 60-80 degrees, and the return air inlet flap rotates at 60-80 degrees. Maintain this temperature for 20-30 hours until all the tobacco leaves in the kiln are completely dry. The time interval between forward and reverse rotation of the circulating fan is 1.5 hours. During the drying stage of the four layers of tobacco in the dense curing barn, the wet bulb temperature should not exceed 41.5℃.

2. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, The dimensions of both the hot air inlet and the return air outlet are 2700mm × 400mm.

3. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for standard dense drying barns with a smoke load greater than 360 rods, the dry bulb temperature is 38–40°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air vent flap is 30–40 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air vent flap is 30–40 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 50–60 degrees.

4. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for standard dense drying barns with a smoke load of less than 360 rods, the dry bulb temperature is 38–40°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air vent flap is 40–50 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air vent flap is 50–60 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 60–70 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air vent flap is 60–70 degrees.

5. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for fresh tobacco leaves with a moisture content greater than 85%, the dry-bulb temperature is 38–40°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry-bulb temperature is 42°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry-bulb temperature is 44°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry-bulb temperature is 47–48°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry-bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 50–60 degrees; the dry-bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 50–60 degrees.

6. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for fresh tobacco leaves with a moisture content of less than 85%, the rotation angle of the return air inlet flap is 50 to 60 degrees when the dry bulb temperature is 38 to 40°C; 40 to 50 degrees when the dry bulb temperature is 42°C; 40 to 50 degrees when the dry bulb temperature is 44°C; 50 to 60 degrees when the dry bulb temperature is 47 to 48°C; 60 to 70 degrees when the dry bulb temperature is 53 to 54°C; and 60 to 70 degrees when the dry bulb temperature is 53 to 54°C.

7. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for the lower fresh tobacco leaves, the dry bulb temperature is 38–40°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 42°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry bulb temperature is 44°C, and the rotation angle of the return air inlet flap is 30–40 degrees; the dry bulb temperature is 47–48°C, and the rotation angle of the return air inlet flap is 40–50 degrees; the dry bulb temperature is 53–54°C, and the rotation angle of the return air inlet flap is 50–60 degrees. The dry bulb temperature is 53-54℃, and the rotation angle of the return air vent flap is 50-60 degrees.

8. The method for tobacco curing based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, for the upper and middle fresh tobacco leaves, when the dry bulb temperature is 38–40°C, the rotation angle of the return air inlet flap is 50–60 degrees; when the dry bulb temperature is 42°C, the rotation angle of the return air inlet flap is 40–50 degrees; when the dry bulb temperature is 44°C, the rotation angle of the return air inlet flap is 40–50 degrees; when the dry bulb temperature is 47–48°C, the rotation angle of the return air inlet flap is 50–60 degrees; and when the dry bulb temperature is 53–54°C, the rotation angle of the return air inlet flap is 60–70 degrees. The dry bulb temperature is 53-54℃, and the rotation angle of the return air vent flap is 60-70 degrees.

9. A method for curing tobacco leaves based on the air volume adjustment of the curing barn according to claim 1, characterized in that, In steps S2 to S4, the bidirectional axial flow circulating fan adopts frequency conversion technology. Before 38℃ and after 60℃, the frequency is 20-30Hz. From the start of stable temperature baking at 38℃ to 42℃ and from the start of stable temperature baking at 48℃ to the end of stable temperature baking at 60℃, the frequency is 30-40Hz. From the start of stable temperature baking at 42℃ to 48℃, the frequency is 40-50Hz.

10. A method for curing tobacco leaves based on the air volume adjustment of the curing barn according to claim 1, characterized in that, When there are contradictions in the rotation angle of the return air vent flap based on the amount of tobacco loaded in the curing barn, the moisture content of the tobacco leaves, and the tobacco leaves in different parts, the return air volume should be adjusted according to the principle that the amount of tobacco loaded in the curing barn is more important than the moisture content of the tobacco leaves, and the moisture content of the tobacco leaves is more important than the tobacco leaves in different parts.

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