Microwave fluidized bed heat pump combined drying device based on flue-cured tobacco lamina distribution and control method

Abstract

A microwave fluidized bed heat pump combined drying device based on tobacco strip distribution and a control method are suitable for the field of tobacco processing equipment, and the device mainly comprises a microwave drying chamber, a high-speed camera, a touch screen, a temperature and humidity sensor, a return air speed meter, an optical fiber temperature sensor, a hot air heat exchanger, a return air centrifugal fan, an air inlet valve and other main components. The control system has the functions that a camera is used for collecting tobacco strip images to obtain the tobacco strip distance, the tobacco strip floating condition and the ignition condition are observed, and the air speed and the air direction are changed by adjusting and controlling the opening size and direction of an air inlet valve. Spontaneous combustion of sharp corners of the tobacco strips during microwave heating due to too small distance between the tobacco strips is prevented. And a multi-path optical fiber temperature sensor is combined to monitor the temperature and the form change rate of the tobacco strips, and the microwave power is controlled to prevent too high temperature and too fast drying. A temperature and humidity sensor on the loop is used for detecting relative humidity and controlling the moisture removal fan to be turned on and turned off. The flue-cured tobacco can be quickly and uniformly dried, and the flue-cured tobacco drying device has the advantages of low energy consumption and high product quality and is suitable for large-scale industrial application.

Description

Technical Field

[0001] This invention belongs to the field of tobacco drying, specifically relating to a combined microwave fluidized bed heat pump drying device and method for drying tobacco materials. Background Technology

[0002] In the tobacco processing industry, the drying of tobacco flakes is a crucial step in ensuring the quality of the final product and maintaining its excellent sensory characteristics. However, existing drying technologies have many limitations and cannot meet the refined quality control requirements of tobacco flakes, a high-value agricultural product. Hot air drying, the most widely used drying method in tobacco flake processing, works by heating the material through convection heating with heated air. This method has significant drawbacks: Firstly, the moisture content of tobacco flakes is unevenly distributed during hot air drying. Areas with lower moisture content will further lose water, making them more prone to breakage in subsequent processing, directly affecting the integrity and economic value of the product. Secondly, traditional hot air drying (especially electric or steam heating methods) is significantly affected by environmental climate. In rainy weather conditions, the relative humidity of the drying medium is high, significantly reducing its moisture-carrying capacity, leading to a sharp decline in tobacco flake drying efficiency, increased energy consumption, and a tendency to produce color differences and uneven quality.

[0003] Microwave drying, as a bulk heat source heating method, has the characteristic of heating from the inside out, which can even out the internal moisture content of tobacco flakes to a certain extent, and the heating speed is fast. However, microwave drying alone poses significant safety hazards and quality control challenges when processing tobacco flakes. Due to the selective heating effect of microwaves on moisture, the heating rate is extremely fast in areas of tobacco flakes with low initial moisture content. If the microwave power and heating time are not properly controlled, local overheating or even carbonization can easily occur, seriously threatening production safety and damaging the sensory quality and commercial value of the tobacco flakes.

[0004] To overcome the shortcomings of single drying methods, the tobacco industry has explored combined drying technologies that integrate multiple methods. The heat pump-microwave combined drying unit combines the bulk heat source effect and selective heating advantage of microwave drying with the active dehumidification and heating capabilities of heat pump drying. This provides a stable, low-temperature, low-humidity drying environment, significantly mitigating the adverse effects of high external humidity conditions. This combination effectively reduces the drying time of tobacco leaves, improves drying efficiency, and better preserves the original structure and color of the tobacco.

[0005] Although existing combined drying equipment has improved in energy efficiency and drying uniformity, its control systems mostly still rely on traditional macroscopic parameter sensors such as temperature, humidity, and wind speed. These systems lack the ability to perceive the physical state of the tobacco flakes themselves during the drying process (such as distribution density, morphological changes, and adhesion). Specifically, for drying materials such as tobacco flakes that are prone to adhesion and have high requirements for stratification, existing technologies cannot effectively solve the following two core problems:

[0006] Lack of control over the uniformity of tobacco flake distribution: Within the fluidized bed drying chamber, tobacco flakes are prone to overlapping, sticking, and localized aggregation due to their inherent characteristics. This aggregation not only affects drying uniformity but, more importantly, in the microwave field, the densely packed tobacco flakes are highly susceptible to localized overheating due to the concentrated electric field intensity, posing a potential quality and safety hazard. Currently, there is a lack of control methods capable of real-time monitoring and proactive adjustment of tobacco flake distribution.

[0007] The drying process is judged by a single indicator: existing systems mostly judge the drying process indirectly by preset time or ambient temperature and humidity, which cannot directly obtain key physical characteristics that reflect changes in the internal moisture content of tobacco leaves (such as morphological changes such as shrinkage rate and curling degree of tobacco leaves). This results in insufficient precision in controlling the drying process and affects the uniformity and quality of the final product.

[0008] In summary, there is an urgent need for an intelligent combined drying technology and device capable of real-time sensing and control of the distribution of tobacco flakes within the drying chamber, while simultaneously and accurately judging the drying process based on the physical changes of the tobacco flakes themselves. Only by deeply integrating machine vision, fiber optic temperature measurement, and heat pump-microwave combined drying technology to construct a closed-loop control system that can adaptively adjust according to the actual distribution and state of the tobacco flakes can the safety, quality, and efficiency issues faced by existing technologies in the tobacco flake drying process be fundamentally resolved, meeting the stringent requirements for raw material quality in high-end tobacco products. Summary of the Invention

[0009] The purpose of this invention is to provide a microwave fluidized bed heat pump combined drying device and control method based on tobacco leaf distribution, which solves the problems of uneven tobacco leaf distribution, inaccurate drying process control, high energy consumption, and poor safety in existing tobacco drying technologies.

[0010] The objective of this invention is achieved through the following technical solution:

[0011] A microwave fluidized bed heat pump combined drying device based on smoke distribution includes a microwave drying chamber, a high-speed camera and light source module for real-time acquisition of smoke images inside the drying chamber, a hopper installed in the drying chamber, a touch screen for centralized system control, and a hot air circulation system connected to the drying chamber. The hot air circulation system consists of a return air duct, a cyclone separator, a recovery duct, a hot air heat exchanger, an inlet regulating electric heating tube, an inlet centrifugal fan, a condenser heat exchanger, an inlet hood, and inlet valves. The return air duct is located at the top of the drying chamber, and the inlet valves are located in the inlet channel at the bottom of the drying chamber. There are three inlet valves: left, middle, and right. A return air velocity measuring instrument, a temperature and humidity sensor, and a dehumidifying fan are installed in the return air duct. The hopper is shaped like a flared mouth, wider at the top and narrower at the bottom, and has ventilation holes evenly distributed on its walls. Multiple fiber optic temperature sensors are installed in the hopper.

[0012] Furthermore, multiple fiber optic temperature sensors are installed at different heights in the hopper inside the drying chamber to monitor the surface temperature of the tobacco flakes.

[0013] Furthermore, the microwave drying chamber is equipped with an opening and closing door, and a transparent observation window is provided on the opening and closing door. The high-speed camera and light source module are located outside the transparent observation window.

[0014] Furthermore, a return air velocity measuring instrument and a temperature and humidity measuring instrument are installed in the return air duct.

[0015] The system's fan and air inlet valve are centrally controlled via a touchscreen; the air inlet valve is an air inlet butterfly valve, installed in the air inlet pipe near the bottom of the hopper, and the valve opening degree and opening direction can be adjusted to regulate the wind speed and air separation in the cavity, ensuring uniform distribution of tobacco flakes.

[0016] A control method for drying tobacco flakes using the aforementioned combined drying device is disclosed. After the tobacco flakes are placed in the dryer and the drying chamber door is closed, the device starts operation. The system achieves efficient drying through multi-threaded parallel control: a high-speed camera captures real-time images of the tobacco flakes, identifies their distribution and spacing, and dynamically adjusts the opening of the left and right butterfly valves and the fan speed to prevent tobacco flakes from accumulating and igniting; simultaneously, an image analysis thread continuously calculates the tobacco flake shrinkage rate and shape change rate to determine the drying stage and moisture content changes; a fiber optic temperature sensor monitors the surface temperature of the tobacco flakes and works in conjunction with a microwave power control thread to maintain it within the 55℃–95℃ range; a return air temperature and humidity sensor monitors the humidity signal and independently controls the start and stop of the exhaust fan; all control threads work collaboratively to achieve synchronous regulation of distribution, temperature, humidity, and drying process until the tobacco flake shrinkage rate reaches approximately 16%, indicating that its moisture content has been dried to approximately 10%, at which point the drying process automatically ends.

[0017] Furthermore, the method for identifying the distribution and spacing of tobacco leaves is as follows: The distance between tobacco leaves is measured using punctuation marks, and the specific steps are as follows:

[0018] (1) Obtain the pixel coordinates (x1,x2),(y1,y2) of the two cigarettes in the image;

[0019] (2) Calculate the pixel spacing of the smoke sheet using the Euclidean distance formula:

[0020]

[0021] (3) Unit conversion to obtain the actual distance:

[0022] D = d pixel ×pixelSize

[0023] Where d pixel The pixel spacing is the distance between the two points, and pixelSize is the pixel size.

[0024] Furthermore, the specific method for dynamically adjusting the opening of the left and right butterfly valves and the fan speed is as follows: the fan speed and direction are controlled by controlling the size and direction of the butterfly valve openings. When the average spacing of the suspended smoke flakes in the drying chamber of the hopper is found to be less than 2mm, the fan inverter frequency is increased to increase the air speed in the chamber and thus increase the smoke flake spacing. If the smoke flake spacing is greater than 6mm, the fan inverter frequency is reduced to decrease the air speed and save fan energy. Initially, the opening of the butterfly valves in the left and right ventilation ducts is set to 80%, and the smoke flakes gather in the left corner of the hopper. The opening of the left ventilation butterfly valve is then adjusted to 90%, and the opening of the right ventilation butterfly valve is adjusted to 70%. The smoke flakes gather in the right corner of the hopper. The opening of the right ventilation butterfly valve is then adjusted to 90%, and the opening of the left ventilation butterfly valve is adjusted to 70% to ensure uniform distribution of the smoke flakes.

[0025] Furthermore, the image analysis thread continuously calculates the tobacco shrinkage rate and shape change rate, and determines the drying stage and moisture content change. This means using the tobacco shrinkage characteristics in the image to determine the tobacco drying process. The specific steps for analyzing the degree of tobacco shrinkage using image analysis are as follows:

[0026] Step 1: After image acquisition, the first step is to remove image noise. Median filtering algorithm is used to remove noise from the image to ensure image clarity and avoid the influence of stray light or other substances on image quality.

[0027] Step 2: Image enhancement is performed. Histogram equalization is used to enhance the contrast of the image, especially in low-light environments, which can improve the recognition accuracy of smoke particles. Then, grayscale transformation is performed to standardize the grayscale of the image, eliminating brightness differences under different shooting conditions and ensuring consistency in subsequent processing.

[0028] Step 3: After image preprocessing, an automatic thresholding segmentation algorithm is used to extract the tobacco flakes, converting the image into a binary image and extracting the contour and area of ​​the tobacco flakes. The tobacco flake area shrinkage rate (calculated by averaging all photos, taking the average of all tobacco flakes) and tobacco flake shape (the ratio of contour perimeter to area, after normalization) are obtained. Based on the shrinkage rate and tobacco flake shape, the shrinkage rate and shape change rate are calculated every 10 seconds for use in determining and calculating the drying rate.

[0029] Step 4: During the drying process of tobacco flakes, area shrinkage occurs due to water loss. The degree of shrinkage is used to judge the drying progress. Based on experience, as the shrinkage rate (calculated by averaging all photographed tobacco flakes) increases from 0 to approximately 11%, the initial moisture content of the tobacco flakes decreases from 20% to 15%. In the second stage, when the shrinkage rate increases from 10% to 13%, the moisture content decreases from 15% to 12%. In the third stage, when the shrinkage rate increases from 13% to 16%, the moisture content decreases from 12% to 10%, and drying is complete.

[0030] Furthermore, a fiber optic temperature sensor collects the surface temperature signal of the tobacco flakes in real time. This temperature signal is compared with a preset threshold, and the microwave heating power is dynamically adjusted. When the temperature drops to the preset lower limit threshold of 55°C, the control system immediately increases the heating power to the preset high power state of 900W, causing the cavity temperature to rise rapidly. When the temperature exceeds the preset upper limit threshold of 95°C, microwave heating is turned off, ensuring that the temperature remains within a reasonable range throughout the drying process, achieving uniform and stable drying of the tobacco flakes. Combining the method of controlling microwave power based on the tobacco flake shrinkage rate and the rate of change in tobacco morphology, if the shrinkage rate exceeds a set threshold (e.g., 0.2% / s), the current microwave heating power is automatically reduced by 100W; if it is below the threshold (e.g., 0.1% / s), the heating temperature is increased, and the current microwave power is automatically increased by 100W. If the rate of change in shape exceeds a set threshold (e.g., 0.05 / s), indicating that the tobacco flakes are curling too quickly, the current microwave heating power is automatically reduced by 100W.

[0031] Furthermore, temperature and humidity sensors collect real-time data on the temperature and humidity parameters of the airflow within the duct circuit. When the detected relative humidity exceeds a preset threshold of 70%, the exhaust fan activates to accelerate the removal of moisture from the cavity, ensuring a high drying rate. When the relative humidity falls below the preset threshold of 50%, the exhaust fan shuts off, recovering the humid and hot air and improving energy efficiency. This closed-loop control maintains suitable humidity within the drying cavity, ensuring product quality.

[0032] The beneficial effects of this invention are that it enables real-time monitoring and active adjustment of tobacco flake distribution, improves drying uniformity, reduces safety hazards, and achieves precise control of the drying process by combining tobacco flake morphology changes with temperature and humidity parameters; it integrates the advantages of heat pump and microwave drying, making it energy-efficient and suitable for continuous industrial production; and it improves the drying quality of tobacco flakes while maintaining their original structure and sensory characteristics. Attached Figure Description

[0033] Figure 1 A schematic diagram of the device structure of the present invention (the figure below is a top view of the figure above);

[0034] Figure 2 Flowchart of the present invention for image recognition of smoke gap and control of air valve opening and direction;

[0035] Figure 3 Flowchart of the drying process control of this invention;

[0036] Figure 1The components are marked as follows: 1. Dryer base box, 2. Condenser heat exchanger, 3. Inlet centrifugal fan, 4. Glass observation window, 5. Drying chamber, 5.1 Drying chamber door, 6. Door closing limit switch, 7. Magnetron, 8. Touch screen, 9. Return air duct, 10. Return air velocity meter, 11. Temperature and humidity sensor, 12. Exhaust fan, 13. Cyclone separator, 14. Recovery duct, 15. Hopper, 16. Fiber optic temperature sensor, 17. Inlet air velocity sensor, 18. Inlet butterfly valve, 19. Inlet hood, 20. Hot air heat exchanger, 21. Inlet air regulator (electric heating element), 22. Fresh air inlet, 23. Centrifugal fan housing, 24. Return air centrifugal fan, 25. Infrared temperature sensor, 26. High-speed camera and light source module. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings (embodiments):

[0038] The structure of the combined drying device of the present invention is as follows: Figure 1 As shown:

[0039] A microwave fluidized bed heat pump combined drying device based on smoke distribution includes a microwave drying chamber 5, a high-speed camera and light source module 26 for real-time acquisition of smoke images in the drying chamber, a hopper 15 set in the drying chamber, a touch screen 8 for centralized system control, and a hot air circulation system connected to the drying chamber. The hot air circulation system consists of a return air duct 9, a cyclone separator 13, a recovery duct 14, a hot air heat exchanger 20, an air inlet regulating electric heating tube 21, an air inlet centrifugal fan 3, a condenser heat exchanger 2, an air inlet hood 19, and an air inlet valve 18. The return air duct 9 is located at the top of the drying chamber 5, and the air inlet butterfly valve 18 is located in the air inlet channel at the bottom of the drying chamber. The air inlet butterfly valve 18 includes three valves: left, middle, and right. A return air velocity measuring instrument 10, a temperature and humidity sensor 11, and a dehumidifying fan 12 are installed in the return air duct 9. The hopper 15 is shaped like a flared mouth with a larger top and a smaller bottom, and the hopper wall is evenly distributed with ventilation holes. Multiple fiber optic temperature sensors 16 are installed in the hopper 15.

[0040] Furthermore, multiple fiber optic temperature sensors 16 are installed at different heights in the hopper 15 of the drying chamber to monitor the surface temperature of the tobacco flakes.

[0041] Furthermore, the microwave drying chamber 5 is equipped with an opening and closing door 5.1, and a transparent observation window 4 is provided on the opening and closing door. The high-speed camera and light source module 24 are located outside the transparent observation window.

[0042] Furthermore, a return air velocity meter 10 and a temperature and humidity meter 11 are installed in the return air duct 9, and an infrared sensor 25 is installed above the drying chamber to measure the temperature of the sheet smoke.

[0043] The system's fans (including the inlet centrifugal fan 3, the return centrifugal fan 24, and the exhaust fan 12) and the inlet butterfly valve 18 are all centrally controlled via the touch screen 8; the inlet butterfly valve 18 can adjust the valve opening size and opening direction to regulate the wind speed and air separation in the cavity, ensuring uniform distribution of smoke.

[0044] The control method for drying tobacco flakes using a combined drying device is as follows: Tobacco flakes are placed into the hopper inside the dryer, and the drying chamber door is closed before the device starts operating. The system achieves efficient drying through multi-threaded parallel control: a high-speed camera captures real-time images of the tobacco flakes, identifies their distribution and spacing, and dynamically adjusts the opening of the left and right butterfly valves and the fan speed to prevent tobacco flakes from accumulating and igniting; simultaneously, an image analysis thread continuously calculates the tobacco flake shrinkage rate and shape change rate to determine the drying stage and moisture content changes; a fiber optic temperature sensor monitors the surface temperature of the tobacco flakes and works in conjunction with a microwave power control thread to maintain it within the 55℃–95℃ range; a return air temperature and humidity sensor monitors the humidity signal and independently controls the start and stop of the exhaust fan; all control threads work collaboratively to achieve synchronous control of distribution, temperature, humidity, and the drying process until the tobacco flake shrinkage rate reaches approximately 16% (moisture content 10%), at which point drying automatically ends.

[0045] The control method of the present invention includes the following steps:

[0046] The process of identifying the gap between smoke sheets and controlling the air valve is as follows: Figure 2 As shown, a high-speed camera acquires images of tobacco leaves and transmits them to an image processing unit. Image processing algorithms are used to identify the positions of the tobacco leaves and calculate the spacing between them. The specific method for identifying the tobacco leaf spacing is as follows:

[0047] (1) Obtain the pixel coordinates (x1,x2),(y1,y2) of the two cigarettes in the image;

[0048] (2) Calculate the pixel spacing of the smoke sheet using the Euclidean distance formula:

[0049]

[0050] (3) Unit conversion to obtain the actual distance:

[0051] D = d pixel ×pixelSize

[0052] Where d pixel The pixel spacing is between the two points, and pixelSize is the pixel size. The pixel size is then converted to the actual size.

[0053] After collecting the smoke flake spacing, if the average spacing is less than 2mm, increase the fan frequency and wind speed to disperse the smoke flakes; if the average spacing is greater than 6mm, decrease the fan frequency to reduce energy consumption; adjust the opening of the left and right air valves according to the smoke flake concentration location to achieve uniform distribution.

[0054] Drying process judgment and control process as follows Figure 3 As shown, the acquired tobacco flake images are preprocessed (denoising, enhancement, and segmentation); the tobacco flake area is extracted to determine the degree of shrinkage; the drying stage is determined based on the degree of shrinkage and the preset moisture content model; the microwave power is dynamically adjusted in conjunction with fiber optic temperature sensor data: if the temperature is below 55℃, the power is increased to 900W; if the temperature is above 95℃, microwave heating is turned off; the power is finely adjusted according to the shrinkage rate to prevent carbonization or low efficiency.

[0055] The present invention will now be described in detail with reference to the accompanying drawings and two specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0056] Example 1: Laboratory-level control scheme based on precise process research

[0057] This embodiment is applicable to a laboratory environment, focusing on the precise calibration of process parameters and model verification, providing a data foundation for industrial scale-up.

[0058] 1. System Configuration and Initial Parameter Settings

[0059] Drying device: such as Figure 1 The small-scale experimental microwave fluidized bed heat pump combined drying device shown has a drying chamber 5 with an effective volume of 50 liters. Vision system: The high-speed camera and light source module 26 uses an industrial camera with a resolution of 2048×2048 and a frame rate of 30fps, coupled with a uniform backlight to ensure clear, shadow-free images. Sensing system: Three fiber optic temperature sensors 16 are installed at heights of 10cm, 20cm, and 30cm from the material bed, respectively. The temperature and humidity sensor 11 in the return air duct is a high-precision type. Control interface: All parameters are set and monitored via a touchscreen 8, with a data acquisition frequency of 1 time / second.

[0060] Initial process parameters: Initial microwave power: 600W (low-power start-up for safety). Initial fan frequency: 35Hz, left and right air valve openings both 80%. Dehumidifier fan start / stop thresholds: On when relative humidity >70%, off when relative humidity <50%. Temperature safety thresholds: Upper limit 95℃, lower limit 55℃. Target drying endpoint for sheet tobacco: Moisture content 10%.

[0061] 2. Control process execution

[0062] Tobacco distribution control:

[0063] A high-speed camera acquires an image every second, and the image processing unit identifies the center point of the contours of all smoke flakes within the field of view in real time. The pixel distance between any two smoke flakes is calculated and converted to the actual physical distance (mm) through calibration. The system calculates the average spacing between all smoke flakes in the entire field.

[0064] Control logic: When the system detects an average spacing of <2.5mm over three consecutive sampling periods, it automatically increases the fan frequency by 50Hz to disperse the accumulated smoke using enhanced airflow. When the average spacing >5.5mm and remains so for one minute, the fan frequency is reduced by 35Hz to save energy. If smoke is detected accumulating in the left corner, the left air valve opening is increased to 85%, and the right air valve opening is reduced to 75%, guiding the airflow direction to achieve uniform distribution.

[0065] Drying process and temperature control:

[0066] Image Feature Extraction: The acquired images are processed every 10 seconds. Through median filtering, histogram equalization, and Otsu automatic thresholding, the contour of each individual tobacco leaf is accurately extracted, and its area and perimeter are calculated. The system records the initial area of ​​the tobacco leaf and calculates the area shrinkage rate in real time (averaging across all tobacco leaves in the captured images). Based on the empirical model summarized in the patent (shrinkage rate 0%–11% corresponds to moisture content of 20%–15%, 11%–13% corresponds to 15%–12%, and 13%–16% corresponds to 12%–10%), the system automatically determines the current drying stage.

[0067] Microwave power control:

[0068] Basic temperature control: If any fiber optic temperature sensor reading exceeds 95°C, immediately shut down the microwave magnetron (7); if all sensor readings are below 55°C, increase the microwave power to 800W.

[0069] Fine-tuning based on morphology: The system calculates the average shrinkage rate and shape change rate of the entire sheet of tobacco every 10 seconds. If the average shrinkage rate is >0.15% / s, the system determines that the drying is too fast and there is a risk of carbonization, and automatically reduces the microwave power by 50W. If the average shrinkage rate is <0.08% / s, the system determines that the drying efficiency is too low, and automatically increases the microwave power by 50W. If the shape change rate is >0.04s... -1 This indicates that the tobacco leaves are curling too quickly, increasing internal stress. The microwave power is automatically reduced by 50W to alleviate the drying stress.

[0070] Humidity control: Real-time data on return air humidity is used to control the exhaust fan 12. Exhaust is activated when the humidity exceeds 65% for 10 seconds; it is deactivated when the humidity remains below 45% for 30 seconds. This setting effectively maintains drying power in small laboratory spaces while preventing excessive energy loss.

[0071] This embodiment, through high-precision image recognition and frequent adjustments, is suitable for studying the morphological changes of tobacco leaves under different drying conditions, providing reliable data support for establishing accurate drying mathematical models and optimizing industrial control parameters. Experiments show that this method can control the standard deviation of the moisture content of the final product within 0.5%, effectively verifying the feasibility of the morphology-based drying process judgment method.

Claims

1. A microwave fluidized bed heat pump combined drying device based on tobacco leaf distribution, characterized in that, The system includes a microwave drying chamber, a high-speed camera and light source module for real-time acquisition of images of the smoke inside the drying chamber, a hopper located in the drying chamber, a touch screen for centralized system control, and a hot air circulation system connected to the drying chamber. The hot air circulation system consists of a return air duct, a cyclone separator, a recovery duct, a hot air heat exchanger, an inlet regulating electric heating tube, an inlet centrifugal fan, a condenser heat exchanger, an inlet hood, and inlet valves. The return air duct is located at the top of the drying chamber, and the inlet valves are located in the inlet channel at the bottom of the drying chamber. There are three inlet valves: left, middle, and right. A return air velocity measuring instrument, a temperature and humidity sensor, and a dehumidifying fan are installed in the return air duct. The hopper is shaped like a flared mouth, wider at the top and narrower at the bottom, and has ventilation holes evenly distributed on its walls. Multiple fiber optic temperature sensors are installed in the hopper.

2. The combined drying apparatus according to claim 1, characterized in that: Multiple fiber optic temperature sensors are installed at different heights in the hopper to monitor the temperature of the tobacco flakes.

3. The combined drying apparatus according to claim 1, characterized in that: The microwave drying chamber is equipped with an opening and closing door, and a transparent observation window is provided on the opening and closing door. The high-speed camera and light source module are located outside the transparent observation window.

4. The combined drying apparatus according to claim 1, characterized in that: The return air duct is equipped with a return air velocity meter and a temperature and humidity meter.

5. The combined drying apparatus according to claim 1, characterized in that: The system's fan and air inlet valve are centrally controlled via a touchscreen; the air inlet valve is an air inlet butterfly valve, installed in the air inlet pipe near the bottom of the hopper, and the valve opening degree and opening direction can be adjusted to regulate the wind speed and air separation in the cavity, ensuring uniform distribution of tobacco flakes.

6. A method for controlling the drying of tobacco flakes using the combined drying apparatus described in claims 1-5, characterized in that: After the tobacco flakes are placed into the dryer and the drying chamber door is closed, the device starts operating. The system achieves efficient drying through multi-threaded parallel control: a high-speed camera captures real-time images of the tobacco flakes, identifies their distribution and spacing, and dynamically adjusts the opening of the left and right butterfly valves and the fan speed to prevent the tobacco flakes from accumulating and igniting; simultaneously, the image analysis thread continuously calculates the shrinkage rate and shape change rate of the tobacco flakes to determine the drying stage and moisture content changes; a fiber optic temperature sensor monitors the surface temperature of the tobacco flakes and works in conjunction with the microwave power control thread to maintain it within the range of 55℃–95℃; a return air temperature and humidity sensor monitors the humidity signal and independently controls the start and stop of the exhaust fan; all control threads work together to achieve synchronous regulation of distribution, temperature, humidity, and drying process until the tobacco flake shrinkage rate reaches approximately 16%, indicating that its moisture content has been dried to approximately 10%, at which point the drying process automatically ends.

7. The control method according to claim 6, characterized in that: The method for identifying the distribution and spacing of tobacco leaves is as follows: The distance between tobacco leaves is measured using punctuation marks. The specific steps are as follows: (1) Obtain the pixel coordinates (x1,x2),(y1,y2) of the two cigarettes in the image; (2) Calculate the pixel spacing of the smoke sheet using the Euclidean distance formula: (3) Unit conversion to obtain the actual distance: D=d pixel ×pixelSize Where d pixel The pixel spacing is the distance between the two points, and pixelSize is the pixel size.

8. The control method according to claim 6, characterized in that: The specific method for dynamically adjusting the opening of the left and right butterfly valves and the fan speed is as follows: the fan speed and direction are controlled by controlling the size and direction of the butterfly valve openings. When it is found that the average spacing between the suspended tobacco flakes in the drying chamber above the hopper is less than 2mm, the fan inverter frequency is increased to increase the air speed in the chamber and increase the spacing between the tobacco flakes. If the spacing between the tobacco flakes is greater than 6mm, the fan inverter frequency is reduced to decrease the air speed and save fan energy. Initially, the opening of the butterfly valves in the left and right ventilation ducts is set to 80%, and the tobacco flakes gather in the left corner of the silo. The opening of the butterfly valve in the left ventilation duct is then adjusted to 90%, and the opening of the butterfly valve in the right ventilation duct is adjusted to 70%. The tobacco flakes gather in the right corner of the silo. The opening of the butterfly valve in the right ventilation duct is then adjusted to 90%, and the opening of the butterfly valve in the left ventilation duct is adjusted to 70% to ensure uniform distribution of the tobacco flakes.

9. The control method according to claim 6, characterized in that: The image analysis thread continuously calculates the shrinkage rate and shape change rate of tobacco leaves, and determines the drying stage and moisture content changes. This means using the shrinkage characteristics of tobacco leaves in images to determine the drying process. The specific steps for analyzing the degree of shrinkage of tobacco leaves using images are as follows: Step 1: After image acquisition, the first step is to remove image noise. Median filtering algorithm is used to remove noise from the image to ensure image clarity and avoid the influence of stray light or other substances on image quality. Step 2: Image enhancement is performed. Histogram equalization is used to enhance the contrast of the image, especially in low-light environments, which can improve the recognition accuracy of smoke particles. Then, grayscale transformation is performed to standardize the grayscale of the image, eliminating brightness differences under different shooting conditions and ensuring the consistency of subsequent processing. Step 3: After image preprocessing, an automatic threshold segmentation algorithm is used to extract the tobacco flakes and convert the image into a binary image. The contour and area of ​​the tobacco flakes are extracted, and the area shrinkage rate and shape of the tobacco flakes are obtained. Based on the shrinkage rate and shape of the tobacco flakes, the shrinkage rate and shape change rate are calculated every 10 seconds for the purpose of determining and calculating the drying rate. Step 4: During the drying process of tobacco flakes, the area shrinks due to water loss. The drying progress is judged by the degree of tobacco flake shrinkage. Based on experience, when the tobacco flake shrinkage rate increases from 0 to about 11%, the initial moisture content of the tobacco flakes decreases from 20% to 15%. In the second stage, when the shrinkage rate increases from 10% to 13%, the moisture content decreases from 15% to 12%. In the third stage, when the shrinkage rate increases from 13% to 16%, the moisture content decreases from 12% to 10%, and the drying process ends.

10. The control method according to claim 6, characterized in that: The surface temperature signal of the tobacco flakes is collected in real time by an optical fiber temperature sensor. The temperature signal is compared with a preset threshold, and the microwave heating power is dynamically adjusted. When the temperature drops to the preset lower limit threshold of 55°C, the control system immediately increases the heating power to the preset high power of 900W to rapidly raise the cavity temperature. When the temperature exceeds the preset upper limit threshold of 95°C, the microwave heating is turned off to ensure that the temperature is always kept within a reasonable range during the drying process, achieving uniform and stable drying of the tobacco flakes. The microwave power is controlled by combining the shrinkage rate and shape change rate of the tobacco flakes. If the shrinkage rate exceeds the set threshold, for example, 0.2% / s, the current microwave heating power is automatically reduced by 100W. If it is below the threshold, for example, 0.1% / s, the heating temperature is increased, and the current microwave power is automatically increased by 100W. If the shape change rate exceeds the set threshold, for example, 0.05 / s, it indicates that the tobacco flakes are curling too quickly, and the current microwave heating power is automatically reduced by 100W. The temperature and humidity sensor collects the temperature and humidity parameters of the airflow in the duct circuit in real time. When the detected relative humidity exceeds the preset threshold of 70%, the dehumidification fan is turned on to accelerate the discharge of moisture from the cavity and ensure the drying rate. When the relative humidity is lower than the preset threshold of 50%, the dehumidification fan is turned off to recover the humid and hot air and improve energy utilization.

Images