A rotary microwave vacuum pyrolysis device modified from a household microwave oven

Abstract

This invention belongs to the field of microwave vacuum pyrolysis technology, and relates to a turntable microwave vacuum pyrolysis device modified from a household microwave oven. It includes a vacuum pump, a drying device, a microwave oven, a rotating device with a mechanical seal, a pressure sensor, and a relay. The vacuum pump is connected to the drying device, and the rotating device is connected to both the drying device and the pressure sensor. A turntable is provided inside the microwave oven, and a vacuum chamber is located on the turntable. The rotating device passes through the microwave oven and connects to the vacuum chamber. The vacuum chamber is connected to the pressure sensor, which is connected to a computer. The pressure sensor detects the pressure within the vacuum chamber. The relay controls the switching on and off of the power supply to the vacuum pump based on the pressure displayed by the pressure sensor. This invention improves the uneven heating during pyrolysis, maintaining the vacuum level of the reaction chamber while preventing microwave leakage caused by drilling holes in the modified household microwave oven.

Description

Technical Field

[0001] This invention belongs to the field of microwave vacuum pyrolysis technology, and more specifically, relates to a turntable microwave vacuum pyrolysis device modified from a household microwave oven. Background Technology

[0002] Biomass pyrolysis reactors are a crucial component of biomass pyrolysis technology. The type and technical specifications of the reactor directly affect the product distribution and quality of biomass pyrolysis. Pyrolysis reactors are diverse, often distinguished by the heating and movement methods of the biomass feedstock and heat carrier. Examples include mechanically contacting rotary cone reactors, ablation reactors, and combined heating circulating fluidized bed reactors and jet bed reactors. However, these traditional pyrolysis reactors are limited by the shortcomings of heat conduction heating methods and cannot be improved. Microwave heating, as a novel heating method, has been applied in many fields and has recently begun to be used in pyrolysis. Microwaves refer to electromagnetic waves with frequencies between 300MHz and 300GHz, between infrared radiation and radio waves in the electromagnetic spectrum, i.e., electromagnetic waves with wavelengths between 1mm and 1m. Based on wavelength and frequency, they can be divided into four bands: decimeter waves, centimeter waves, millimeter waves, and submillimeter waves. Microwaves mainly possess three characteristics: penetration, reflection, and absorption. Polar molecules in the medium can be heated by microwaves. Under the influence of rapidly changing microwaves, polar molecules will change their polar orientation in response to variations in the external electric field. Microwave heating causes water molecules to spin, converting microwave energy into heat energy in the material being heated. This leads to a rapid increase in the material's temperature, resulting in a series of physicochemical processes, including thermochemical reactions, ultimately achieving microwave pyrolysis. Microwave heating utilizes the principle of dielectric loss and employs a holistic heating method. It directly heats materials through molecular polarization and ionic conductivity, offering advantages such as rapid heating and high thermal efficiency. However, microwave heating has a significant drawback: uneven heating. Furthermore, current research on microwave pyrolysis technology in a vacuum environment is limited. Maintaining the vacuum level within the reaction chamber while avoiding microwave leakage caused by modifications to the microwave oven remains a challenge. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a turntable microwave vacuum pyrolysis device modified from a household microwave oven. By installing a turntable in the microwave heating cavity, the material rotates in the resonant cavity, thereby overcoming the problem of uneven heating in the prior art.

[0004] To achieve the above objectives, this invention is implemented through the following technical solution: a turntable-type microwave vacuum pyrolysis device modified from a household microwave oven, comprising a vacuum pump, a drying device, a microwave oven, a rotating device with a mechanical seal, a pressure sensor connected to a computer, and a relay. The vacuum pump is connected to the drying device, and the rotating device is connected to both the drying device and the pressure sensor. A turntable is provided inside the microwave oven, and a vacuum chamber is provided on the turntable. The rotating device passes through the microwave oven and connects to the vacuum chamber. The vacuum chamber is connected to the pressure sensor, which detects the pressure within the vacuum chamber. The relay controls the switching on and off of the power supply to the vacuum pump based on the pressure displayed by the pressure sensor. The turntable drives the vacuum chamber and the rotating device to rotate, and the vacuum pump, drying device, rotating device, and vacuum chamber are interconnected. The rotating device helps to homogenize the absorption of microwaves by the material during heating, and the silicone gasket adsorbs water vapor at low pressure within the rotating device, helping to maintain the vacuum level.

[0005] Preferably, the rotating device includes a bushing with a T-valve at the top and the bottom connected to the microwave oven. The bushing contains a rotary joint, a free shaft, a hexagonal connector, a Teflon tube, and a Teflon female connector. The lower end of the T-valve is rotatably connected to the upper end of the rotary joint. The lower end of the rotary joint is sequentially connected to the free shaft, hexagonal connector, Teflon tube, and Teflon female connector. The lower end of the Teflon tube is connected to the vacuum chamber, and the Teflon female connector is located within the vacuum chamber. The T-valve, rotary joint, free shaft, hexagonal connector, Teflon tube, and Teflon female connector are interconnected, and all connections are sealed with sealing rings. Maintaining a seal at all connections preserves the vacuum level within the vacuum chamber.

[0006] Preferably, the bushing includes a first bushing and a second bushing, with the lower end of the first bushing connected to the upper end of the second bushing.

[0007] Preferably, the first bushing is a nylon bushing with a TC latex head at the bottom, the second bushing is a stainless steel bushing with a TC connector at the top and a flange at the bottom, and a TC silicone gasket is provided between the first bushing and the second bushing.

[0008] Preferably, the first bushing and the second bushing are connected by a clamp.

[0009] Preferably, the rotary joint is a single fluid rotary joint, and the rotating device has only one fluid channel.

[0010] Preferably, the lower end of the free shaft is rotatably connected to a Teflon shaft, and the lower end of the Teflon shaft is rotatably connected to a vacuum chamber.

[0011] Preferably, the hexagonal connector is laterally connected to the side of the free shaft and vertically connected to the Teflon tube.

[0012] Preferably, calcium oxide is used as a desiccant in the drying apparatus.

[0013] Preferably, the microwave oven includes a power switch, and a light source and a fan are installed inside the microwave oven cavity. The light source is used to observe the internal reaction of the microwave oven, and the fan is used to dissipate heat from the microwave oven cavity.

[0014] The present invention has the following beneficial effects:

[0015] (1) The microwave pyrolysis biomass reaction device of the present invention improves the uneven heating during the pyrolysis process; the equipment is simple, small in size and easy to operate, and can complete the continuous heating operation, which is convenient for operation and management and provides a basis for making larger equipment; microwave heating is fast, relatively uniform, without temperature gradient, and volume heating without hysteresis effect, which ensures the quality of the heated products; it can make biomass raw materials heat up quickly and undergo pyrolysis, which has the advantages of energy saving and consumption reduction; it realizes the automatic control of microwave heating and can also modify the heating program to flexibly meet production requirements.

[0016] (2) The present invention adds a turntable to the multimode vacuum microwave pyrolysis device, which not only maintains the vacuum level of the reaction chamber, but also avoids microwave leakage caused by drilling holes in the household microwave oven. The present invention maintains the vacuum level without being detected by microwave detectors, which meets national safety and health standards. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the microwave vacuum pyrolysis device of the present invention;

[0018] Figure 2 This is a schematic diagram of the rotating device in this invention;

[0019] Figure 3 This is a schematic diagram showing the effect of microwave power on the iodine adsorption value and yield of activated carbon.

[0020] In the diagram: 1 Vacuum pump, 2 Drying device, 3 Rotary device, 4 Microwave oven, 5 Vacuum chamber, 6 Pressure sensor, 7 T valve, 8 Rotary joint, 9 Free shaft, 10 TC silicone gasket, 11 Second bushing, 12 First bushing, 13 Hexagonal joint, 14 Teflon tube, 15 Teflon female head, 16 Teflon shaft. Detailed Implementation

[0021] The embodiments of the present invention will be disclosed below with reference to the drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the present invention. That is, in some embodiments of the present invention, these practical details are not essential. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0022] A rotary microwave vacuum pyrolysis device modified from a household microwave oven includes a vacuum pump 1, a drying device 2, a microwave oven 4, a rotating device 3, a pressure sensor 6, and a relay (the relay is not labeled in the figure). The microwave oven includes a power switch. The microwave oven 4 has a built-in light source in its cavity. Turning on the light source switch allows observation of the internal reaction. The microwave oven cavity also has a built-in fan. Due to the high reaction temperature during pyrolysis, turning on the fan switch can dissipate heat from the microwave oven cavity to a certain extent. The fan indicator light shows whether the fan is operating normally. The internal structure of the microwave oven is existing technology, and those skilled in the art can make conventional selections as needed. No further limitations are made here. Calcium oxide is used as a desiccant in the drying device 2.

[0023] Vacuum pump 1 is connected to drying device 2, and rotating device 3 is connected to drying device 2 and pressure sensor 6 respectively.

[0024] The microwave oven is modified from a household microwave oven, with an internal space of 45L. Its magnetron has a maximum output power of 1000W and a frequency of 2450MHz. The microwave oven 4 contains a turntable, on which is a vacuum chamber 5. The vacuum chamber is made of polypropylene, which is non-toxic, colorless, odorless, and has excellent dielectric properties (dielectric constant, ε=2.2, loss tangent, tanδ= 0.0003-0.0004) and mechanical strength.

[0025] The rotating device 3 passes through the microwave oven 4 and is connected to the vacuum chamber 5. The vacuum chamber 5 is connected to the pressure sensor 6 connected to the computer. The pressure sensor 6 detects the pressure inside the vacuum chamber 5. The relay controls the power supply of the vacuum pump 1 to be turned on and off according to the pressure displayed by the pressure sensor 6.

[0026] The turntable drives the vacuum chamber 5 and the rotating device 3 to rotate. The vacuum pump 1, drying device 2, rotating device 3, and vacuum chamber 5 are interconnected. A pressure sensor is connected to the vacuum pump and microwave oven through a pipeline, which can monitor the pressure of the reaction environment in real time. When the pressure in the environment is lower than the set start pressure, the controller outputs 220V to power the vacuum pump. When the vacuum level reaches the set stop pressure, the controller outputs no power. This process repeats, keeping the vacuum level in the microwave reaction chamber essentially constant.

[0027] The rotating device helps to homogenize the absorption of microwaves by the material during the heating process. The rotating device 3 includes a first bushing 12 and a second bushing 11. The first bushing 12 is a nylon bushing with a TC latex head at the bottom. The second bushing 11 is a stainless steel bushing with a TC connector at the top and a flange at the bottom. A TC silicone gasket 10 is provided between the first bushing 12 and the second bushing 11. The silicone gasket adsorbs water vapor at low pressure in the rotating device to help maintain the vacuum degree of the device. The first bushing 12 and the second bushing 11 are connected by a stainless steel clamp.

[0028] The top of the first bushing 12 is equipped with a T valve 7, and the bottom of the second bushing 11 is connected to the microwave oven 4 through an internal threaded connector. The bushing is equipped with a rotary joint 8, a free shaft 9, a hexagonal joint 13, a Teflon tube 14, and a Teflon female head 15. The rotary joint adopts a single fluid rotary joint structure.

[0029] The lower end of T valve 7 is rotatably connected to the upper end of rotary joint 8. The lower end of rotary joint 8 is connected to free shaft 9. Hexagonal joint 13 is laterally connected to the side of free shaft 9 and vertically connected to Teflon tube 14. The lower end of Teflon tube 14 is connected to Teflon female head 15. The lower end of Teflon tube 15 is connected to vacuum chamber 5. Teflon female head 15 is located inside vacuum chamber 5.

[0030] The lower end of the free shaft 9 is rotatably connected to the Teflon shaft 16, and the lower end of the Teflon shaft 16 is rotatably connected to the vacuum chamber 5;

[0031] The T-valve 7, rotary joint 8, free shaft 9, hexagonal joint 13, Teflon tube 14, and Teflon female head 15 are interconnected, and all connections are sealed with sealing rings. There is only one fluid channel in the rotating device (dashed line part).

[0032] Microwave energy attenuates when it passes through a circular waveguide with a diameter smaller than that allowing power to propagate freely. Such circular waveguides are generally called "cut-off tubes" and are widely used in the design of microwave cavity openings. The power attenuation rate is a function of its wavelength and the radius of the cut-off tube, based on the following attenuation constant:

[0033]

[0034] Where λ c (Cutoff wavelength) = 3.413 × tube radius, λ0 (wavelength in unbounded medium) = 0.1224m, the tube radius measured in this study is 0.02185m, and the attenuation is 580dB / m obtained from the formula.

[0035] When measured at a distance of 5 cm from the emission source, the maximum output radiation intensity of industrial equipment and electrical appliances should not exceed 1 mW / cm². 2 .

[0036]

[0037] Therefore, for the microwave oven used, the minimum cut-off tube length is (13.03dB) / (580dB / m) = 0.0225m. Due to deformation in the edge region of the cut-off waveguide and microwave operating area, there is an uncertainty in the attenuation rate in this region. Therefore, an additional length of one cut diameter is added before completely leaving the waveguide, equivalent to 0.0225 + 0.0437 = 0.0662m. On the other hand, the Teflon shaft and Teflon tube are adequate in terms of attenuation due to the low dielectric constant of the cut-off tube. Therefore, the final design length of the cut-off tube is 0.07m.

[0038] The microwave vacuum pyrolysis apparatus provided by this invention is used to perform pyrolysis analysis on waste cotton residue, as detailed below:

[0039] (1) After drying the waste cotton residue at 105℃ for 24 hours, weigh 4g of it and mix it with 2g of ferrous sulfate and 12g of 60% phosphoric acid for 24 hours (phosphoric acid is used as an activator and ferrous sulfate is used as an auxiliary agent). Place it near the edge of the round tray in the vacuum chamber.

[0040] (2) Close the microwave oven door. In evaluating the effect of microwave power on pyrolysis, the microwave oven is operated at five power levels: 300W, 400W, 500W, 600W, and 700W.

[0041] (3) The microwave oven operates in a timed cycle, repeating from maximum power to zero power. In this study, the microwave cycle was 29 seconds. At a power level of 1000W, the magnetron was always in the "on" state. At a power level of 700W, the magnetron was "on" within 20 seconds and "off" within 9 seconds. At a power level of 600W, the magnetron was "on" within 17 seconds and "off" within 12 seconds. At a power level of 500W, the magnetron was "on" within 14 seconds and "off" within 15 seconds. At a power level of 400W, the magnetron was "on" within 11 seconds and "off" within 18 seconds.

[0042] (4) Investigate the effect of microwave power in the range of 300~700 W on the iodine adsorption value and yield of activated carbon from waste cotton residue. See Figure 3 .

[0043] With increasing microwave power, the iodine adsorption value increased synchronously, while further increases in microwave power led to a decrease in the iodine adsorption value. The maximum iodine adsorption value reached 1180 mg / g at a microwave power of 500 W. It can also be seen that the rate of increase in iodine adsorption value from 300 W to 500 W was significantly higher than the rate of decrease after 500 W. With increasing microwave power, the yield of activated carbon from waste cotton residue showed a trend of first increasing and then decreasing. Below 500 W, the yield increased with increasing microwave power. Because the energy transferred by microwave radiation is relatively small at low power, the heat received by the raw material is insufficient, resulting in insufficient activation reaction and leaving room for increased activated carbon yield. With increasing microwave power, the activation reaction of waste cotton residue further increased, and the yield reached its peak at 500 W.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. However, the above description is merely a specific embodiment of the present invention, and the technical features of the present invention are not limited thereto. Any other embodiments derived by those skilled in the art without departing from the technical solution of the present invention should be covered within the patent scope of the present invention.

Claims

1. A rotary microwave vacuum pyrolysis device modified from a household microwave oven, characterized in that, Includes a vacuum pump (1), a drying device (2), a microwave oven (4), a rotating device (3) with a mechanical seal, a pressure sensor (6) connected to a computer, and a relay. The vacuum pump (1) is connected to the drying device (2), and the rotating device (3) is connected to the drying device (2) and the pressure sensor (6) respectively. The microwave oven (4) is equipped with a turntable, and a vacuum chamber (5) is provided on the turntable. The rotating device (3) passes through the microwave oven (4) and is connected to the vacuum chamber (5). The vacuum chamber (5) is connected to the pressure sensor (6). The pressure sensor (6) detects the pressure in the vacuum chamber (5). The relay controls the power supply of the vacuum pump (1) to be turned on and off according to the pressure displayed by the pressure sensor (6). The turntable drives the vacuum chamber (5) and the rotating device (3) to rotate, and the vacuum pump (1), the drying device (2), the rotating device (3), and the vacuum chamber (5) are interconnected. The rotating device (3) includes a bushing, with a T valve (7) at the top inside the bushing and the bottom of the bushing connected to the microwave oven (4). The bushing contains a rotary joint (8), a free shaft (9), a hexagonal joint (13), a Teflon tube (14), and a Teflon female head (15). The lower end of the T valve (7) is rotatably connected to the upper end of the rotary joint (8). The lower end of the rotary joint (8) is sequentially connected to the free shaft (9), the hexagonal joint (13), the Teflon tube (14), and the Teflon female head (15). The lower end of the Teflon tube (14) is connected to the vacuum chamber (5), and the Teflon female head (15) is located inside the vacuum chamber (5). The T valve (7), rotary joint (8), free shaft (9), hexagonal joint (13), Teflon tube (14), and Teflon female head (15) are interconnected, and each connection is sealed with a sealing ring. The bushing includes a first bushing (12) and a second bushing (11), with the lower end of the first bushing (12) connected to the upper end of the second bushing (11); The first bushing (12) and the second bushing (11) are connected by a clamp; The rotary joint (8) is a single fluid rotary joint, and the rotary device (3) has only one fluid channel; The lower end of the free shaft (9) is rotatably connected to the Teflon shaft (16), and the lower end of the Teflon shaft (16) is rotatably connected to the vacuum chamber (5). The hexagonal connector (13) is laterally connected to the side of the free shaft (9) and vertically connected to the Teflon tube (14).

2. The rotary microwave vacuum pyrolysis device modified from a household microwave oven according to claim 1, characterized in that, The first bushing (12) is a nylon bushing with a TC latex head at the bottom, and the second bushing (11) is a stainless steel bushing with a TC connector at the top and a flange at the bottom. A TC silicone gasket (10) is provided between the first bushing (12) and the second bushing (11).

3. The rotary microwave vacuum pyrolysis device modified from a household microwave oven according to claim 1, characterized in that, The drying device (2) uses calcium oxide as a desiccant.

4. The rotary microwave vacuum pyrolysis device modified from a household microwave oven according to claim 1, characterized in that, The microwave oven (4) includes a power switch. A light source and a fan are installed inside the cavity of the microwave oven (4). The light source is used to observe the internal reaction of the microwave oven (4), and the fan is used to dissipate heat from the cavity of the microwave oven (4).

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