Continuous and efficient microwave expansion device, and control method therefor and use thereof

Abstract

The present invention provides a continuous and efficient microwave expansion device, comprising a microwave module, a circulating air module, and a material conveying module. When a circulating induced draft fan (18) of the circulating air module operates, and when the flowing direction of circulating air in a metal microwave cavity (1) is from an upper air hood (12) to a lower air hood (13), the air pressure in a lower cavity (102) is less than the air pressure in an upper cavity (101) which is less than atmospheric pressure, forming a slight negative pressure state. The present invention ensures, by maintaining a slight negative pressure state in the microwave expansion device, that the air pressure inside and outside the cavity remains substantially balanced, and has the advantages of a simple and reliable structure, smooth material flow, and prevention of material breakage and jamming during conveying. It is confirmed after continuous operation tests that the microwave expansion device of the present invention can better avoid phenomena such as oxidative browning, blackening, and even burning of tobacco stems at high temperatures, further improving the expansion quality of tobacco stems, and making the product have a bright color and distinct aroma.

Description

Continuous and efficient microwave expansion device, its control method and application

[0001] This invention claims a priority claim numbered AEP2024-02947, with a priority date of November 5, 2024, in the United Arab Emirates. Technical Field

[0002] This invention relates to microwave expansion equipment, and more particularly to a continuous and efficient microwave expansion device applicable to expanding tobacco stems, as well as a control method and application of the device. Background Technology

[0003] Tobacco stems, the coarse, hard veins of tobacco leaves, are a byproduct of the tobacco industry and have some economic value. To achieve the reuse of tobacco stems, existing technologies typically employ microwave expansion processes (such as Chinese invention patent application CN1387802A). This involves microwave-treating the tobacco stems and then cutting them into shreds to obtain expanded stem shreds suitable for tobacco products. To ensure the product's expansion rate, the microwave treatment requires a very high power density. Because tobacco stems are small, strip-shaped materials, under high-power-density microwave radiation with insufficient uniformity, localized areas subjected to extremely high energy treatment are prone to sparking, leading to scorching and burning of the tobacco stems, which in turn affects production continuity. Conversely, areas with insufficient energy cannot expand properly, reducing material utilization and expansion rate. Therefore, a common challenge in this technical field is ensuring that the tobacco stem material receives uniform high-power-density microwave energy to prevent sparking.

[0004] To address this challenge, Chinese invention patent application CN102613687A proposed a device for microwave expansion. Based on a conventional microwave heating chamber and material conveyor belt structure, it introduces a gaseous heating medium from the top of the microwave heating chamber, vertically spraying it onto the material. This gaseous heating medium improves the uniformity of heating the material, and the gas is collected at the bottom for recycling. However, in practical applications, this device failed to effectively solve the technical difficulties. Analysis revealed that when the gaseous heating medium is positively pressurized from the top of the chamber onto the tobacco stem material, although the conveyor belt and the tobacco stem material are not dense, there is significant resistance to the vertically sprayed gas. This creates a "flow resistance band" above the material, causing some of the vertically sprayed gas to be obstructed and change direction, subsequently diffusing outwards from the top of the material. This portion of gas reaches the side wall of the chamber and flows back upwards, forming a backflow and turbulence, losing its ability to pass through the gaps between the tobacco stems and the conveyor belt. If a gap is created between the side wall of the microwave heating chamber and the edge of the conveyor belt to avoid creating a "flow resistance zone," another portion of the gas will flow through this gap without passing through the tobacco stems and into the bottom of the chamber. This causes the gaseous heat medium to lose its function of improving heating uniformity. Therefore, the device is less effective than expected in improving the heating uniformity of the material, and it cannot prevent sparking caused by uneven heating. On the other hand, due to gas backflow and turbulence within the heating chamber, airlocks need to be installed at the inlet and outlet of the device to prevent high-temperature gas from overflowing. Because tobacco stems and expanded tobacco stems are small in volume and light in weight, they are prone to jamming and crushing when passing through the airlocks, seriously affecting the utilization rate of the tobacco stems. In addition, the inventors also found that the gas nozzles of the device, which are located at the top of the microwave heating chamber, need to be made of microwave-transparent material to avoid affecting microwaves. However, due to the high temperature and airflow environment inside the chamber, the tar in the tobacco stems will contaminate these components, thereby affecting microwave transmission and burning them, resulting in a high frequency of device downtime for maintenance. Summary of the Invention

[0005] The purpose of this invention is to address the difficulties existing in the prior art by providing a microwave expansion device with high heating uniformity. When processing materials with high power density, it can ensure that the materials are heated evenly, avoid local overheating and arcing, and ultimately achieve higher material utilization and expansion.

[0006] To achieve the above objectives, the present invention provides a continuous and efficient microwave expansion device, the device comprising a microwave module, a circulating air module and a material conveying module, the microwave module comprising a metal microwave cavity 1, a microwave power supply antenna 3 mounted on the top wall of the metal microwave cavity 1 and a microwave generator 2 connected to the antenna, the front end of the metal microwave cavity 1 being provided with a feeding end and the rear end being provided with a discharging end;

[0007] The material conveying module includes a guide roller 71 and a breathable conveyor belt 7 guided by the guide roller 71. The breathable conveyor belt 7 passes through the metal microwave cavity 1 through the feed end and the discharge end, dividing the space inside the metal microwave cavity 1 into an upper cavity 101 and a lower cavity 102.

[0008] The portion of the top wall of the metal microwave cavity 1 without the microwave feed antenna 3 is formed by an upper vent plate 10, and the bottom wall of the metal microwave cavity 1 is formed by a lower vent plate 11. The circulating air module includes an upper vent shroud 12 located on the upper vent plate 10, a lower vent shroud 13 located on the lower vent plate 11, a lower circulating air duct 15 and an upper circulating air duct 14 connecting the upper vent shroud 12 and the lower vent shroud 13, and a circulating fan 18 located on the circulating air duct. When the circulating fan 18 is running, and when the direction of airflow in the metal microwave cavity 1 is from the upper vent shroud 12 to the lower vent shroud 13, the air pressure in the lower cavity 102 is less than the air pressure in the upper cavity 101, which is less than atmospheric pressure.

[0009] In this invention, for ease of description and not limitation, the direction toward feeding is referred to as "front" and the direction toward discharging is referred to as "rear" for the conveyor belt and microwave cavity, and the length direction of the microwave cavity is parallel to the conveying direction of the material in the cavity.

[0010] In a preferred embodiment, the circulating fan 18 is installed on the lower circulating air duct 15, so that the air pressure in the lower cavity 102 is 5 to 500 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 5 to 500 Pa lower than atmospheric pressure. This pressure difference ensures that the microwave cavity is in a slightly negative pressure state.

[0011] More preferably, the air pressure in the lower cavity 102 is 50-300 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 50-300 Pa lower than atmospheric pressure. If the pressure difference is too small, a small amount of circulating hot air will overflow from both ends of the suppressor; if the difference is too large, a large amount of external air will enter the cavity and mix with the circulating hot air, affecting the temperature of the circulating air and possibly blowing away the material.

[0012] Preferably, the air pressure in the lower cavity 102 is 200-300 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 50-100 Pa lower than atmospheric pressure, which can ensure that the circulating hot air can pass through the material vertically from top to bottom evenly and effectively, thereby improving the heat distribution effect.

[0013] For the circulating air module, the circulating air enters from the top of the microwave cavity and is drawn out from the bottom. After some of the exhaust gas is discharged, some fresh air is added as needed, and then it re-enters the microwave cavity to achieve circulation. Therefore, the terms "upstream" and "downstream" should be understood as the relative relationship of the gas flow within the module.

[0014] In this invention, the guide roller 71 is typically composed of multiple rollers. Those skilled in the art can arrange the guide roller 71 according to the length and position of the conveyor belt to ensure the cyclic movement of the breathable conveyor belt 7.

[0015] In this invention, the upper vent plate 10 and the lower vent plate 11 function as a gas distribution device, ensuring that the gas input from the upper hood 12 and output from the lower hood 13 is distributed as evenly as possible to various locations within the cavity. Those skilled in the art can also achieve the same function using other gas distribution devices depending on actual conditions.

[0016] In order to achieve air pressure regulation in the cavity, a preferred embodiment is to install an adjustable air outlet damper 17 on the lower circulation duct 15 and an adjustable air inlet damper 16 on the upper circulation duct 14.

[0017] Those skilled in the art can adjust the size of the air outlet damper 17 and the air inlet damper 16 so that the air pressure near the feed end and the discharge end of the metal microwave cavity 1 is slightly less than or almost equal to the external air pressure.

[0018] Unlike existing positive pressure jet technology, this invention places the circulating fan 18 on the lower circulating air duct 15. By adjusting the air volume of the circulating fan and the size of the air damper 17 and air inlet damper 16, the pressure inside the cavity can be made slightly lower than atmospheric pressure. The air pressure in the lower cavity 102 is slightly lower than the air pressure in the upper cavity 101. Therefore, the gas in the circulating air module is drawn in from the upper hood 12 and enters the upper cavity 101 under negative pressure. Under the action of pressure difference, it passes through the non-dense material and the permeable conveyor belt, and is then extracted from the lower hood 13 at the bottom of the lower cavity 102 for recycling.

[0019] Under the action of micro negative pressure, the upper vent plate 10 and the lower vent plate 11 achieve uniform air distribution, which can effectively prevent the formation of a "flow resistance zone" above the material on the conveyor belt. This ensures that the gas in the cavity can pass smoothly through the material under the guidance of negative pressure instead of spreading upward or around. Therefore, this micro negative pressure design can effectively prevent backflow and turbulence, and ensure that the material with a certain thickness on the conveyor belt can be uniformly radiated.

[0020] On the other hand, when the metal microwave cavity 1 is under a slight negative pressure, the airflow inside the cavity does not have the power to diffuse out of the cavity through the feed end or the discharge end. Therefore, there is no need to set an air lock at the feed end or the discharge end of the cavity, which naturally avoids the phenomenon of material jamming and crushing caused by air lock jetting. On the one hand, it simplifies the equipment structure, and on the other hand, it improves the utilization rate of raw materials.

[0021] In another embodiment of the present invention, a circulating fan 18 is installed on the upper circulating air duct 14. When the circulating fan 18 is running, the airflow direction within the metal microwave cavity 1 is from the lower shroud 13 to the upper shroud 12. Therefore, the air pressure in the upper cavity 101 is less than the air pressure in the lower cavity 102, which is less than atmospheric pressure. Preferably, the air pressure in the upper cavity 101 is 5-500 Pa lower than the air pressure in the lower cavity 102, and the air pressure in the lower cavity 102 is 5-500 Pa lower than atmospheric pressure.

[0022] Similarly, more preferably, the air pressure in the upper cavity 101 is 50-300 Pa lower than the air pressure in the lower cavity 102, and the air pressure in the lower cavity 102 is 50-300 Pa lower than the atmospheric pressure. Particularly preferably, the air pressure in the upper cavity 101 is 200-300 Pa lower than the air pressure in the lower cavity 102, and the air pressure in the lower cavity 102 is 50-100 Pa lower than the atmospheric pressure, to ensure that the circulating air can flow vertically from the lower cavity to the upper cavity.

[0023] Choosing an appropriate pressure difference between the upper and lower chambers can improve the efficiency of the circulating air passing vertically through the material pile. If the pressure difference is too small or too large, it may reduce the efficiency of the circulating hot air passing vertically through the material from top to bottom, affecting the auxiliary heating effect of the circulating hot air on the material, and may also disrupt the negative pressure conditions in the upper chamber.

[0024] In this invention, to prevent gas from flowing out between the edge of the conveyor belt and the inner wall of the cavity, the width of the ventilated conveyor belt 7 should match the width of the metal microwave cavity 1. To ensure the position of the conveyor belt within the cavity and minimize gaps, a preferred embodiment is to provide a guide mechanism along the length of the cavity on the inner sides of the left and right walls of the metal microwave cavity 1. The guide mechanism has a conveyor belt insertion groove 35 and a guide groove 34 along the length of the cavity.

[0025] The breathable conveyor belt 7 includes a breathable mesh belt 31 and an impermeable belt 32 arranged on both sides of the breathable mesh belt 31 along the length direction, and a guide limiting edge 33 is provided along the edge of the impermeable belt 32 along the length direction.

[0026] When the edge of the airtight belt 32 is located in the conveyor belt insertion groove 35, the guide limit edge 33 engages with the guide groove 34. Through the engagement of the guide groove 34 and the guide limit edge 33, it is ensured that the airtight conveyor belt 7 is always taut, and the gas in the cavity can only pass through the material and the conveyor belt under the action of slight negative pressure, but cannot flow between the conveyor belt and the inner wall of the cavity.

[0027] According to another embodiment, the metal microwave cavity 1 further includes wave-transparent side baffles 41 arranged on the left and right sides of the cavity along the length direction of the cavity. The top of the wave-transparent side baffles 41 abuts against the top wall of the metal microwave cavity 1 and the bottom of the wave-transparent side baffles 41 abuts against the bottom wall of the metal microwave cavity 1. The wave-transparent side baffles 41 divide the internal space of the metal microwave cavity 1 into an inner cavity 42 and a cavity partition 43.

[0028] The guide mechanism is arranged along the length of the cavity on the inner sides of the left and right walls of the inner cavity 42;

[0029] The width of the breathable conveyor belt 7 matches the width of the inner cavity 42. When the edge of the non-breathable belt 32 is located in the conveyor belt insertion groove 35, the guide limit edge 33 cooperates with the guide groove 34.

[0030] In this invention, the airtight strip 32 is not used for stacking materials, but rather to prevent airflow from escaping near the side walls of the cavity. The width of the airtight strip 32 on one side is 50-1000 mm, preferably 100-250 mm. This is because commonly used microwave generators are typically 915 MHz or 2450 MHz, with corresponding microwave wavelengths λ of approximately 327 mm and 122 mm, respectively. When the distance between the material and the two cavity walls is too small, especially less than λ / 4, the microwave heating efficiency will decrease and the heating uniformity will decline. When the distance is greater than λ / 4, the heating uniformity will improve, but if the distance is too large, the cavity space utilization will decrease. Therefore, an area of ​​approximately (λ / 4) to (3λ / 4) is chosen as the width of the airtight strip on one side. Thus, an airtight strip 32 with a width of 100-250 mm is suitable for common 915 MHz or 2450 MHz microwave devices.

[0031] If the width is too small, the material will be too close to the microwave cavity wall, causing uneven heating. If the width is too large, it will reduce the space utilization of the cavity. Those skilled in the art can set an appropriate width according to the processing capacity of the microwave device. The material is piled on the breathable mesh belt 31 to ensure that the airflow in the cavity can flow through the material, thereby improving the uniformity of heating.

[0032] Preferably, the breathable mesh belt 31, the impermeable belt 32, the guide limiting edge 33, and the guiding mechanism are made of glass fiber material coated with polytetrafluoroethylene. The breathable mesh belt 31 has a thickness of 0.1-2 mm to ensure necessary belt strength and ease of manufacture; the equivalent diameter of the mesh openings is 1-20 mm, preferably 2-4 mm, to ensure that fine materials do not easily penetrate or clog the mesh openings, and that circulating air can pass through the mesh surface; the impermeable belt 32 has a thickness of 0.1-2 mm.

[0033] To ensure the stability of the circulating air module during continuous operation, it is preferable to install an exhaust gas duct 22 downstream of the circulating exhaust fan 18, with an exhaust gas exhaust fan 24 and an adjustable exhaust gas damper 23 installed on the exhaust gas duct 22; and to install a fresh air supply duct 19 upstream of the inlet damper 16, with a fresh air supply fan 21 and an adjustable fresh air supply damper 20 installed on the fresh air supply duct 19.

[0034] Optionally, a feed suppressor 5 is provided at the feed end of the metal microwave cavity 1, and a discharge suppressor 6 is provided at the discharge end. In one embodiment, a suppressor bracket 51 is fixed at the feed end and the discharge end of the metal microwave cavity 1, and the fixing height should be slightly higher than the height of the conveyor belt. Multiple downward protrusions 52 are provided on the suppressor bracket 51.

[0035] In this invention, the material stacking thickness is typically 10-200 mm.

[0036] As another preferred embodiment, a heat insulation layer 25 is provided on the outer wall of the metal microwave cavity 1 to reduce heat loss inside the cavity.

[0037] Preferably, the microwave expansion device further includes a circulating air heater disposed on the upper circulating air duct 14.

[0038] In this invention, both the microwave feed antenna 3 and the microwave generator 2 are commercially available components, and their connection and installation can be performed according to the product manual. Common 915MHz or 2450MHz microwave feed antennas 3 and microwave generators 2 can be used in the technical solution of this invention. Those skilled in the art can also set an appropriate number of microwave feed antennas 3 according to the size of the microwave cavity to ensure that the material on the conveyor belt can fully absorb energy.

[0039] The present invention also provides the application of the above-mentioned continuous and efficient microwave expansion device in expanding tobacco stems.

[0040] Furthermore, the present invention also provides a control method for the above-mentioned continuous and efficient microwave expansion device, the method comprising the following steps:

[0041] 1. Start the circulating exhaust fan 18 to make the metal microwave cavity 1, the lower hood 13, and the lower circulating air duct 15 all under negative pressure. Adjust the opening of the exhaust damper 17 and the intake damper 16 to make the upper cavity 101 and the lower cavity 102 under slight negative pressure. Turn on the circulating air heater.

[0042] 2. Start the fresh air supply fan 21 and the exhaust gas exhaust fan 24. Adjust the fresh air supply damper 20 and the exhaust gas exhaust damper 23 to make the exhaust gas flow rate 100%-150% of the fresh air supply flow rate, so that the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state under gas circulation.

[0043] 3. Place the material in the middle of the breathable conveyor belt 7. Under the action of the feed suppressor 5, the material is spread flat on the breathable mesh belt 31 of the conveyor belt. The thickness of the material spread is 10-200mm. Start the microwave generator 2 so that the material enters and passes through the metal microwave cavity 1 with the breathable conveyor belt 7 and is radiated by microwaves until the material utilization rate reaches 80%-99% based on the total material quantity and the volume expansion reaches 200%-400% based on the total material volume.

[0044] 4. Adjust the power of the exhaust fan 24 and the opening of the exhaust damper 23 to discharge excess water vapor from the cavity, ensuring that the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state during operation.

[0045] In this invention, a slightly negative pressure state refers to a situation where, when the circulating air flows from the upper shroud 12 to the lower shroud 13 within the metal microwave cavity 1, the air pressure in the lower cavity 102 is 5-500 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 5-500 Pa lower than atmospheric pressure. More preferably, the air pressure in the lower cavity 102 is 50-300 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 50-300 Pa lower than atmospheric pressure. Particularly preferably, the air pressure in the lower cavity 102 is 200-300 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is 50-100 Pa lower than atmospheric pressure.

[0046] Alternatively, the circulating air can flow in the opposite direction. That is, when the circulating air flows from the lower shroud 13 to the upper shroud 12 in the metal microwave cavity 1, the air pressure in the upper cavity 101 is 5 to 500 Pa lower than the air pressure in the lower cavity 102, and the air pressure in the lower cavity 102 is 5 to 500 Pa lower than the atmospheric pressure.

[0047] Preferably, since a large amount of water vapor is generated after the material is irradiated, in step 4, the flow rate of excess water vapor discharged from the cavity is 100%-150% of the amount of water vapor generated in the cavity due to the heating of the material, ensuring that the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state during operation.

[0048] In this invention, when the continuous and efficient microwave expansion device is running stably, the circulating air entering the metal microwave cavity 1 is 140-170°C.

[0049] In this invention, since the airflow can effectively pass through the gaps between materials and the mesh of the conveyor belt, it ensures that the tobacco stems of each layer of material in the material pile are uniformly heated by auxiliary external heating, balancing the microwave heating effect and serving as an effective supplement to microwave heating. Therefore, the temperature of the circulating air should be adapted to the temperature of the material passing through the microwave chamber. In order to avoid the circulating hot air temperature being too high and causing the material surface to scorch, it is preferably controlled at 140-170°C, which is beneficial to improving the appearance, color and aroma of the expanded material, especially the expanded tobacco stems.

[0050] Furthermore, the continuous and efficient microwave expansion device and its control method of the present invention can be applied to processing tobacco stems into expanded tobacco stems, and can also be applied to processing other materials (such as tea stems) into expanded products.

[0051] This invention improves the fit between the breathable conveyor belt 7 and the inner walls on both sides of the microwave cavity, avoiding the formation of airflow channels between the breathable conveyor belt 7 and the inner walls on both sides of the microwave cavity. This ensures that the circulating air in the device can pass correctly between the material and the breathable conveyor belt under negative pressure guidance, thereby preventing the circulating air from flowing back or turbulently in the cavity and preventing the jet flow from being blocked and changing direction.

[0052] Because the circulating air is used more efficiently as a gaseous heat medium, the heating uniformity of the material is greatly improved, and the temperature around the material is stable and consistent. Therefore, the heating uniformity is better, avoiding local extreme heating or local insufficient heating. Thus, when using high power density microwave radiation treatment, problems such as material sparking, scorching, and combustion caused by microwaves can also be avoided.

[0053] Once the tobacco stem material stops igniting and charring, the splashing of harmful substances such as tar inside the chamber is significantly reduced, thus significantly improving the pollution inside the chamber and reducing the frequency of downtime maintenance.

[0054] The micro-negative pressure state of this invention can ensure that the air pressure inside and outside the microwave cavity is in a basically balanced state. Therefore, the high-temperature gas inside the cavity has no driving force to escape outward, and the low-temperature air outside the cavity will not enter the cavity in large quantities from the feed end or the discharge end. Therefore, there is no need to set up airlocks or other devices at the feed end or the discharge end. This makes the structure of material entering and exiting the metal microwave cavity simple and reliable, ensures smooth logistics, and avoids material breakage and jamming during the transportation process.

[0055] After continuous operation and testing, the microwave expansion device of the present invention has been confirmed to better avoid oxidation, browning, blackening, and even combustion of tobacco stems at high temperatures, thereby further improving the quality of tobacco stem expansion and making the product bright in color and with a distinct aroma. Attached Figure Description

[0056] Figure 1 is a schematic diagram of the microwave expansion device of the present invention;

[0057] Figure 2 is a schematic diagram of the microwave expansion device of the present invention (from another angle);

[0058] Figure 3 is a front view of the microwave module and the material conveying module of the microwave expansion device of the present invention;

[0059] Figure 4 is a left view of the microwave module and material conveying module (partial) of the microwave expansion device of Embodiment 1;

[0060] Figure 5 is a schematic diagram of the microwave module (partial) of the microwave expansion device in Example 1;

[0061] Figure 6 is a left view of the microwave module and material conveying module (partial) of the microwave expansion device in Embodiment 2;

[0062] Figure 7 is a structural diagram of the breathable conveyor belt of the present invention;

[0063] Figure 8 is a partial enlarged view of the edge of the breathable conveyor belt of the present invention;

[0064] Figure 9 is a schematic diagram of the suppressor structure of the present invention;

[0065] The components include: 1. Metal microwave cavity; 2. Microwave generator; 3. Microwave power antenna; 4. Antenna protective cover; 5. Feed suppressor; 6. Discharge suppressor; 7. Ventilated conveyor belt; 8. Guide side support; 9. Side sealing air plate; 10. Upper air vent plate; 11. Lower air vent plate; 12. Upper air hood; 13. Lower air hood; 14. Upper circulating air duct; 15. Lower circulating air duct; 16. Inlet air damper; 17. Outlet air damper; 18. Circulating exhaust fan; 19. Fresh air replenishment duct; 20. Fresh air replenishment duct. 21. Air damper; 22. Fresh air supply fan; 23. Exhaust duct; 24. Exhaust damper; 25. Exhaust exhaust fan; 36. Insulation layer; 37. Breathable mesh belt; 38. Impermeable belt; 39. Guide limit edge; 30. Guide groove; 31. Conveyor belt insertion groove; 32. Material; 43. Wave-transparent side baffle; 44. Inner cavity; 55. Cavity partition; 66. Suppressor bracket; 77. Protrusion; 88. Guide roller; 99. Upper cavity; 100. Lower cavity. Detailed Implementation

[0066] The following examples are used to explain the technical solutions of the present invention in a non-limiting manner.

[0067] Example 1

[0068] The microwave expansion device shown in Figure 1-2 includes a microwave module, a circulating air module, and a material conveying module.

[0069] The microwave module, as shown in Figure 3-5, includes a metal microwave cavity 1, a microwave feed antenna 3 mounted on the top wall of the metal microwave cavity 1, and a microwave generator 2 connected to the antenna. The front end of the metal microwave cavity 1 is referred to as the feed end, and the rear end as the discharge end, according to the material conveying direction. The portion of the top wall of the metal microwave cavity 1 without the microwave feed antenna 3 is replaced by an upper vent plate 10, and the bottom wall of the metal microwave cavity 1 is formed by a lower vent plate 11, making both the upper and lower walls of the metal microwave cavity 1 breathable structures to ensure that circulating air can pass through.

[0070] The material conveying module includes multiple guide rollers 71 and a breathable conveyor belt 7 guided by the guide rollers 71. The breathable conveyor belt 7 passes through the metal microwave cavity 1 from the inlet end and the outlet end, dividing the space inside the metal microwave cavity 1 into an upper cavity 101 and a lower cavity 102.

[0071] As shown in Figure 7, the breathable conveyor belt 7 includes a breathable mesh belt 31 and impermeable belts 32 arranged on both sides of the breathable mesh belt 31 along its length. Guide limiting edges 33 are provided along the edges of the impermeable belts 32 along their length. The width of the impermeable belt on one side is 25cm, and the width of the breathable mesh belt in the middle is 600mm.

[0072] A pair of guide mechanisms matching the guide limiting edge 33 are provided on the inner sides of the left and right walls of the metal microwave cavity 1 along the length of the cavity. In this embodiment, the guide mechanism on each side consists of a guide side support 8 and a side sealing gas sheet 9 covering its upper part. The gap between the guide side support 8 and the side sealing gas sheet 9 serves as a conveyor belt insertion groove 35, and the upper surface of the guide side support 8 is slotted in the extension direction as a guide groove 34. When the edge of the airtight belt 32 and the guide limiting edge 33 are engaged with the guide mechanism, the edge of the airtight belt 32 is in the conveyor belt insertion groove 35, while the guide limiting edge 33 is in the guide groove 34, so that the ventilated conveyor belt 7 is installed in the cavity and can always move along the guide mechanism with the movement of the guide roller 71, avoiding dislocation. In this case, the width of the ventilated conveyor belt 7 matches the width of the metal microwave cavity 1, so there is no gas flow channel between the edge of the ventilated conveyor belt 7 and the inner wall of the cavity, forcing the gas in the cavity to pass through the vent holes in the middle area of ​​the conveyor belt.

[0073] Both the guiding mechanism and the breathable conveyor belt 7 are made of glass fiber coated with polytetrafluoroethylene. This type of material has a certain strength and has the advantages of being stain-resistant and heat-resistant. The conveyor belt is 1mm thick and the equivalent diameter of the breathable mesh in the middle is 2.5mm.

[0074] The circulating air module includes an upper hood 12 located above the upper vent plate 10, a lower hood 13 located below the lower vent plate 11, a lower circulating air duct 15 and an upper circulating air duct 14 connecting the upper hood 12 and the lower hood 13. An adjustable exhaust damper 17 is installed on the lower circulating air duct 15, and an adjustable inlet damper 16 is installed on the upper circulating air duct 14. A circulating exhaust fan 18 is also installed on the lower circulating air duct 15. A separate exhaust exhaust duct 22 is installed downstream of the circulating exhaust fan 18, and an exhaust exhaust fan 24 and an adjustable exhaust exhaust damper 23 are installed on the exhaust exhaust duct 22. A fresh air supply duct 19 is installed upstream of the inlet damper 16, and a fresh air supply fan 21 and an adjustable fresh air supply damper 20 are installed on the fresh air supply duct 19.

[0075] The airflow and pressure of the circulating air within the circulating air module are controlled by adjusting the power of the three fans and the opening of the four dampers.

[0076] Taking tobacco stems as an example, the operating steps of this microwave expansion device include:

[0077] 1. Start the circulating fan 18 to bring the metal microwave cavity 1, the lower hood 13, and the lower circulating air duct 15 into a negative pressure state. Then adjust the opening of the air outlet damper 17 and the air inlet damper 16 until the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state. Under the slightly negative pressure state, the circulating air can pass through the conveyor belt and circulate normally in the circulating air system, and will not escape from the feed end or the discharge end. The air outside the cavity will also hardly have any driving force to enter the cavity from the feed end or the discharge end. Therefore, the air pressure inside and outside the microwave cavity is in a balanced state.

[0078] 2. Start the fresh air supply fan 21 and the exhaust gas exhaust fan 24. Adjust the fresh air supply damper 20 and the exhaust gas exhaust damper 23 to make the exhaust gas flow rate slightly higher than the fresh air supply flow rate, so that the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state under the gas circulation state.

[0079] 3. Start the material conveying module, pile the material in the middle of the breathable conveyor belt 7, and spread the material on the breathable mesh belt 31 of the conveyor belt under the action of the feed suppressor 5. Adjust the height of the feed suppressor to spread the material about 50mm; start the microwave generator 2.

[0080] 4. When the tobacco stem material is heated, a large amount of water vapor will be generated. Adjust the power of the exhaust fan 24 and the opening of the exhaust damper 23 to discharge the excess water vapor in the cavity, so as to ensure that the upper cavity 101 and the lower cavity 102 are in a slightly negative pressure state and remain stable during operation. The air pressure in the lower cavity 102 is about 200 Pa lower than the air pressure in the upper cavity 101, and the air pressure in the upper cavity 101 is about 50 Pa lower than the atmospheric pressure.

[0081] Because the circulating fan 18 is installed on the lower circulating air duct 15, the airflow in the microwave cavity changes from the conventional "positive pressure injection" to "negative pressure extraction". By adjusting the airflow of the circulating fan, the size of the air outlet damper 17 and the air inlet damper 16, the cavity can be made to be in a slightly negative pressure state. Under the action of negative pressure, the gas is drawn in from the upper hood 12 and enters the upper cavity 101. Under the action of pressure difference, it passes through the non-dense material and the breathable conveyor belt, and is then extracted from the lower hood 13 at the bottom of the lower cavity 102 for recycling.

[0082] This micro-negative pressure prevents the formation of a "flow resistance band" above the material, ensuring that the gas inside the cavity can pass smoothly through the material under the guidance of negative pressure instead of diffusing upwards or around. Therefore, this micro-negative pressure design can effectively avoid backflow and turbulence, ensuring that materials of a certain thickness on the conveyor belt can be uniformly radiated.

[0083] In this embodiment, the tobacco stem raw material is subjected to an expansion process.

[0084] The properties of the tobacco stem raw material before entering the expansion device are as follows:

[0085] The bulk density of this batch of tobacco stem raw materials is approximately 380 kg / m³. 3 The raw material has a moisture content of approximately 12 wt%.

[0086] Adjust the position of the feed suppressor so that the average stack height of the tobacco stem raw material is about 30mm and the average stack width is 600mm.

[0087] The microwave module uses a 915MHz microwave feed antenna 3 and a microwave generator 2, with a circulating air temperature of approximately 165℃.

[0088] The average material utilization rate of the expanded tobacco stems after passing through the discharge suppressor is 99% by weight of raw materials, and the average bulk density of the material is approximately 95 kg / m³. 3 The volume expansion is 400% of the total raw material volume, and the average stack height is about 120mm.

[0089] The microwave energy consumption is approximately 45 kW·h / t of expanded tobacco stem product.

[0090] After 24 hours of continuous operation, observation revealed that due to the constant slight negative pressure within the silo, the circulating air effectively passed through the gaps in the tobacco stems and the conveyor belt, preventing reverse backflow and turbulence above the material. Under negative pressure, the material remained stably attached to the breathable conveyor belt without being blown away. Therefore, the airflow velocity had no significant impact on system operation. Inspection of the silo after 24 hours of continuous operation showed no tobacco stems flying up or falling randomly. Testing of the expanded tobacco stems revealed no sparking; only a few stems showed slight localized charring. This localized charring occurred in less than ten grams per ton of expanded tobacco stems, a proportion less than one part per million.

[0091] In comparison, using the existing expansion device disclosed in CN102613687A, processing the same tobacco stem raw material with the same feed parameters, after 24 hours of continuous operation, it was found that approximately 20% of the material in the discharge (based on the feed mass, the same below) was not effectively expanded and basically remained in the state at the time of feeding; approximately 10% of the material showed obvious charring characteristics; and approximately 10% of the material broke into fragments, falling to the bottom of the conveyor belt and being difficult to recover, or popping out from the discharge port, or getting stuck inside the equipment. The average material utilization rate was approximately 60%, and the volume expansion rate was 150% of the total raw material volume.

[0092] In addition, during a shutdown inspection, obvious arcing marks were found on the inner wall of the microwave cavity, with some areas showing brownish-black tar-like substances adhering to or splashing. The outer protective cover of the microwave antenna also showed obvious signs of splashing, indicating serious contamination inside the cavity.

[0093] Therefore, this invention controls the air pressure within the microwave cavity to create a slightly negative pressure device, allowing circulating air to effectively pass through the material. Taking tobacco stems as an example, because the material is heated more evenly, the tobacco stems no longer ignite or char. Therefore, for the equipment, this invention reduces the splashing of harmful substances such as tar within the cavity, thus significantly improving the internal contamination situation and extending the equipment downtime maintenance interval.

[0094] Regarding the materials, the expanded tobacco stems of this invention achieve a raw material utilization rate of 99% and an expansion volume of 400%. No oxidation, browning, blackening, or scorching phenomena were found in the resulting products, effectively improving the quality of tobacco stem expansion.

Claims

A continuous and efficient microwave expansion device, the device includes a microwave module, a circulating air module and a material conveying module. The microwave module includes a metal microwave cavity (1), a microwave feeding antenna (3) installed on the top wall of the metal microwave cavity (1) and a microwave generator (2) connected to the antenna. The front end of the metal microwave cavity (1) is provided with a feeding end and the rear end is provided with a discharging end. The material conveying module includes a guide roller (71) and a breathable conveyor belt (7) guided by the guide roller (71). The breathable conveyor belt (7) passes through the metal microwave cavity (1) through the feed end and the discharge end, dividing the space inside the metal microwave cavity (1) into an upper cavity (101) and a lower cavity (102). Its features The part of the top wall of the metal microwave cavity (1) without the microwave feed antenna (3) is composed of an upper air vent plate (10), and the bottom wall of the metal microwave cavity (1) is composed of a lower air vent plate (11). The circulating air module includes an upper air hood (12) set on the upper part of the upper air vent plate (10), a lower air hood (13) set on the lower part of the lower air vent plate (11), a lower circulating air duct (15) and an upper circulating air duct (14) for connecting the upper air hood (12) and the lower air hood (13), and a circulating fan (18) set on the circulating air duct. When the circulating fan (18) is running, and when the direction of the circulating air flow in the metal microwave cavity (1) is from the upper air hood (12) to the lower air hood (13), the air pressure in the lower cavity (102) is less than the air pressure in the upper cavity (101) and less than atmospheric pressure. The continuous and efficient microwave expansion device according to claim 1 is characterized in that... The air pressure in the lower cavity (102) is 5 to 500 Pa lower than the air pressure in the upper cavity (101), and the air pressure in the upper cavity (101) is 5 to 500 Pa lower than atmospheric pressure. The continuous and efficient microwave expansion device according to claim 1 is characterized in that... The air pressure in the lower cavity (102) is 200-300 Pa lower than the air pressure in the upper cavity (101), and the air pressure in the upper cavity (101) is 50-100 Pa lower than atmospheric pressure. The continuous and efficient microwave expansion device according to claim 1 is characterized in that... An adjustable air outlet damper (17) is installed on the lower circulating air duct (15), and an adjustable air inlet damper (16) is installed on the upper circulating air duct (14). The continuous and efficient microwave expansion device according to claim 1 is characterized in that... A waste gas exhaust duct (22) is installed downstream of the circulating exhaust fan (18), and a waste gas exhaust fan (24) and an adjustable waste gas exhaust damper (23) are installed on the waste gas exhaust duct (22). The continuous and efficient microwave expansion device according to claim 4 is characterized in that... A fresh air supply pipe (19) is installed upstream of the intake air damper (16), and a fresh air supply fan (21) and an adjustable fresh air supply damper (20) are installed on the fresh air supply pipe (19). The continuous and efficient microwave expansion device according to claim 1 is characterized in that... When the circulating fan (18) is running, and when the direction of the circulating air flow in the metal microwave cavity (1) is from the lower hood (13) to the upper hood (12), the air pressure in the upper cavity (101) is less than the air pressure in the lower cavity (102), which is less than atmospheric pressure. The continuous and efficient microwave expansion device according to claim 7 is characterized in that... The air pressure in the upper cavity (101) is 5 to 500 Pa lower than the air pressure in the lower cavity (102), and the air pressure in the lower cavity (102) is 5 to 500 Pa lower than the atmospheric pressure. The continuous and efficient microwave expansion device according to claim 8 is characterized in that... The air pressure in the upper cavity (101) is 200-300 Pa lower than the air pressure in the lower cavity (102), and the air pressure in the lower cavity (102) is 50-100 Pa lower than the atmospheric pressure. The continuous and efficient microwave expansion device according to claim 1 is characterized in that... A guide mechanism is provided on the inner side of the left and right walls of the metal microwave cavity (1) along the length of the cavity. The guide mechanism has a conveyor belt insertion groove (35) and a guide groove (34) along the length of the cavity. The breathable conveyor belt (7) includes a breathable mesh belt (31) and an impermeable belt (32) arranged on both sides of the breathable mesh belt (31) along the length direction, and a guide limiting edge (33) is provided at the edge of the impermeable belt (32) along the length direction; The width of the breathable conveyor belt (7) matches the width of the metal microwave cavity (1). When the edge of the impermeable belt (32) is located in the conveyor belt insertion groove (35), the guide limit edge (33) cooperates with the guide groove (34). The continuous and efficient microwave expansion device according to claim 10 is characterized in that... The metal microwave cavity (1) also includes wave-transparent side baffles (41) arranged on the left and right sides of the cavity along the length of the cavity. The top of the wave-transparent side baffles (41) abuts against the top wall of the metal microwave cavity (1) and the bottom of the wave-transparent side baffles (41) abuts against the bottom wall of the metal microwave cavity (1). The wave-transparent side baffles (41) divide the internal space of the metal microwave cavity (1) into an inner cavity (42) and a cavity partition (43). The guide mechanism is arranged along the length of the cavity on the inner side of the left and right walls of the inner cavity (42); The width of the breathable conveyor belt (7) matches the width of the inner cavity (42). When the edge of the non-breathable belt (32) is located in the conveyor belt insertion groove (35), the guide limit edge (33) cooperates with the guide groove (34). The continuous and efficient microwave expansion device according to claim 1 is characterized in that... A heat insulation layer (25) is provided on the outer wall of the metal microwave cavity (1). The continuous and efficient microwave expansion device according to claim 1 is characterized in that... The microwave expansion device also includes a circulating air heater installed on the upper circulating air duct (14). The application of the continuous and efficient microwave expansion device according to any one of claims 1-14 in expanding tobacco stems. The control method for the continuous and efficient microwave expansion device according to any one of claims 1-6 and 10-13, the method comprising the following steps: (1) Start the circulating fan (18) to make the metal microwave cavity (1), the lower hood (13) and the lower circulating air duct (15) all in a negative pressure state. Adjust the opening of the air outlet damper (17) and the air inlet damper (16) to make the upper cavity (101) and the lower cavity (102) in a slightly negative pressure state. Turn on the circulating air heater. (2) Start the fresh air supply fan (21) and exhaust gas exhaust fan (24). Adjust the fresh air supply damper (20) and exhaust gas damper (23) to make the exhaust gas flow rate 100%-150% of the fresh air supply flow rate, so that the upper cavity (101) and lower cavity (102) are in a slightly negative pressure state under gas circulation. (3) The material is piled in the middle of the breathable conveyor belt (7). Under the action of the feed suppressor (5), the material is spread flat on the breathable mesh belt (31) of the conveyor belt. The thickness of the material is 10-200mm. The microwave generator (2) is started so that the material enters and passes through the metal microwave cavity (1) along with the breathable conveyor belt (7) and is radiated by microwave until the material utilization rate reaches 80%-99% based on the total material quantity and the volume expansion reaches 200%-400% based on the total material volume. (4) Adjust the power of the exhaust fan (24) and the opening of the exhaust damper (23) to discharge excess water vapor in the cavity, and ensure that the upper cavity (101) and the lower cavity (102) are in a slightly negative pressure state during operation. The method according to claim 15, characterized in that The micro-negative pressure is such that the air pressure in the lower cavity (102) is 5 to 500 Pa lower than the air pressure in the upper cavity (101), and the air pressure in the upper cavity (101) is 5 to 500 Pa lower than atmospheric pressure. The method according to claim 16, characterized in that In step (4), the flow rate of excess water vapor discharged from the cavity is 100%-150% of the amount of water vapor generated in the cavity due to the heating of the material. The method according to claim 16, characterized in that When the continuous and efficient microwave expansion device is running stably, the circulating air entering the metal microwave cavity (1) is 140-170°C.

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