Continuous Microwave Vacuum Dryer
Microwave drying process than conventional drying methods and processing to improve product quality, but due to the drying temperature is generally above 70 ℃, dry fast, easy internal gelatinization result in some products, lower product quality; microwave vacuum drying technology vacuum drying and microwave drying the characteristics of organic integration, the use of microwave energy for the dry processing of the material under vacuum conditions, a vacuum environment to ensure the material can be dried at low temperatures, the microwave drying material has instantaneous efficiency, so you can achieve a rapid low-temperature drying of materials [1 ~ 2]. The development of a continuous microwave vacuum drying equipment to ensure the material drying temperature at 40 ℃, drying rate is vacuum hot air dry a few times, greatly increasing the production capacity, and the dry product can effectively maintain the color, smell and taste , shape and nutritional content, improved product quality.
A main structure and key technologies 1.1 Main structure of microwave vacuum drying equipment drying system consisting of a vacuum system and microwave systems. The course of their work as follows: first turn off the flapper valve of access to materials, open the vacuum butterfly valve, start the vacuum pump, vacuum drying chamber to produce a certain degree of vacuum and deflated vacuum cut-off valve to maintain the differential pressure through the electromagnetic vacuum drying chamber. Material continuously into the feed hopper feed system into the microwave vacuum studio, this time sequence start the microwave source, the material of microwave vacuum drying process, roller scraper screw conveyor material, so that the material in the microwave vacuum drying Indoor slow lateral movement of upper and lower radial rotation, you can even microwave energy. System output through the material after the end of the drying treatment, completion of discharge. The device including the feed system, conveying systems, microwave systems, vacuum drying chamber, a feeding system and vacuum system of six parts. Continuous microwave vacuum drying equipment schematic diagram see Figure 1. Feed system conveyor system. Microwave systems. Vacuum drying chamber. A material system. 1.2 key technology of the vacuum system (1) microwave vacuum drying chamber under vacuum, vacuum reduction, reducing the air breakdown field strength, electric field ionization of gas molecules easily to gas breakdown and arc discharge phenomena, the phenomenon is most likely to occur in the microwave feed-forward coupled port and the cavity field strength Depot, will not only consume the microwave energy , and will damage the components and microwave reflection shorten the magnetron service life [3]. In a given range of vacuum and microwave power conditions should be properly designed to determine the structure and size of the microwave vacuum drying room, indoor air breakdown field strength within the safe range. The structure of the microwave vacuum drying chamber should also ensure that the microwave field uniformity, and avoid the overheating of the material medium due in part to the field strength strong, while the other part is due to the weak electric field and heat, the structure of the microwave vacuum drying chamber should also meet the pressure vessel design requirements and specifications.Based on the above design principles, to determine the structure and size parameters of the microwave vacuum drying chamber. (2) microwave vacuum seal structure of microwave vacuum drying equipment connections, both microwave and vacuum double-sealed, microwave leakage control in the safety standards within the vacuum level should also achieve the design requirements. Therefore, the microwave vacuum drying chamber and the feed device interface, the flange and the expected out, etc., it is necessary to a suitable microwave sealing material to prevent microwave leakage, while also using the rubber ring is vacuum sealed to prevent system leakage causing the reduction of the vacuum. Conductive rubber, conductive metal ring and soft ferrite materials such as microwave sealing material according to the junction of the different structure type, respectively. (3) continuous access to material structure for access to material structure to ensure the continuous production, due to the frequent movement access to materials, the structure need to have a good seal to keep the vacuum degree of the whole system and to prevent microwave leakage, so The seal is key to the parts. Vacuum out of the material structure of rotating closed wind device structure, the structure of continuous conveying the good uniform feed, but it is easy sealing, to seal badly worn seal wear causes the vacuum system leak, causing the vacuum instability . At the same time, the gap in the microwave along the seals wear out radiation over radiation safety standards, resulting in the microwave leakage. In this study, the double flapper valve structure of the material from the hopper into the microwave drying chamber, the discharge from the chamber to the atmospheric environment.
Two main components designed 2.1 microwave vacuum drying chamber microwave vacuum drying chamber using a cylindrical cavity, the magnetic field lines of the cylindrical heater is more concentrated material to heat up faster, more suitable for dry material extruded rapid warming requirements, while the cylindrical structure is easy to meet the pressure container design requirements. By the workload, the maximum allowable temperature, vacuum degree of the work and the air breakdown field strength and pressure relationship, determine the maximum safe working electric field strength using the following formula can calculate the work load of the maximum power dissipation density. Microwave power of the unit of drying chamber should be less than the work load of the maximum power dissipation density, which can calculate the minimum volume of the drying chamber, the formula to determine the minimum volume of the drying chamber, and to consider the material coefficient, power density and the microwave field uniformity, and other factors to determine the main parameters of the drying chamber. In the case of constant input power, the larger the size of the cavity mode appears, the more electric field superposition of different modes, making a total of superposition of electric field is uniform in the entire cavity of the body. Another important parameter of the drying chamber is the quality factor, quality factor, said the quality of the resonator, the higher its value, the higher the microwave efficiency of utilization of the 2.2 microwave system Microwave system uses multi-fed mouth independent input of microwave energy to the drying chamber to reduce the The fed can be coupled power density of the mouth to prevent gas breakdown and arc discharge phenomena, each independent microwave sources include microwave power and microwave transmission systems. Microwave power source electrical circuit shown in Figure 2, in which key components magnetron VE, the system uses a continuous wave magnetron, magnetron working properly required voltage provided by dedicated microwave with a high leakage inductance of transformer T, in the 220V AC voltage on the primary winding of the transformer, the secondary low voltage winding for magnetron cathode heating filament voltage at the same time, the secondary high voltage winding kV class high voltage alternating current through the high voltage capacitor C voltage doubler rectifier circuit is composed of high-voltage diode VD, added to the magnetron between the two poles, a negative high voltage for the magnetron cathode. Magnetron work will be distributed a lot of heat, cooling control, easy to use, usually with forced air cooling, and the upcoming fan installed in the magnetron near the heat sink for cooling the work of the magnetron. The microwave transmission system is the magnetron output standard waveguide microwave power to the lowest loss transmission of microwave vacuum drying chamber, the magnetron output antenna plug into a standard waveguide broadside on the hole in the head attached to ensure that its output antenna uniform wire mesh gasket with the flange of the waveguide hole flange contact and then tighten the fixing screws, you can use [4]. Waveguide and the drying chamber junctions Falan Jia a Teflon plate, can block the water vapor in the drying process, the groove of the flange into the rubber ring seal vacuum, vacuum drying chamber environment. The use of soft ferrite ring to prevent microwave leakage.
Microwave drying process than conventional drying methods and processing to improve product quality, but due to the drying temperature is generally above 70 ℃, dry fast, easy internal gelatinization result in some products, lower product quality; microwave vacuum drying technology vacuum drying and microwave drying the characteristics of organic integration, the use of microwave energy for the dry processing of the material under vacuum conditions, a vacuum environment to ensure the material can be dried at low temperatures, the microwave drying material has instantaneous efficiency, so you can achieve a rapid low-temperature drying of materials [1 ~ 2]. The development of a continuous microwave vacuum drying equipment to ensure the material drying temperature at 40 ℃, drying rate is vacuum hot air dry a few times, greatly increasing the production capacity, and the dry product can effectively maintain the color, smell and taste , shape and nutritional content, improved product quality.
A main structure and key technologies 1.1 Main structure of microwave vacuum drying equipment drying system consisting of a vacuum system and microwave systems. The course of their work as follows: first turn off the flapper valve of access to materials, open the vacuum butterfly valve, start the vacuum pump, vacuum drying chamber to produce a certain degree of vacuum and deflated vacuum cut-off valve to maintain the differential pressure through the electromagnetic vacuum drying chamber. Material continuously into the feed hopper feed system into the microwave vacuum studio, this time sequence start the microwave source, the material of microwave vacuum drying process, roller scraper screw conveyor material, so that the material in the microwave vacuum drying Indoor slow lateral movement of upper and lower radial rotation, you can even microwave energy. System output through the material after the end of the drying treatment, completion of discharge. The device including the feed system, conveying systems, microwave systems, vacuum drying chamber, a feeding system and vacuum system of six parts. Continuous microwave vacuum drying equipment schematic diagram see Figure 1. Feed system conveyor system. Microwave systems. Vacuum drying chamber. A material system. 1.2 key technology of the vacuum system (1) microwave vacuum drying chamber under vacuum, vacuum reduction, reducing the air breakdown field strength, electric field ionization of gas molecules easily to gas breakdown and arc discharge phenomena, the phenomenon is most likely to occur in the microwave feed-forward coupled port and the cavity field strength Depot, will not only consume the microwave energy , and will damage the components and microwave reflection shorten the magnetron service life [3]. In a given range of vacuum and microwave power conditions should be properly designed to determine the structure and size of the microwave vacuum drying room, indoor air breakdown field strength within the safe range. The structure of the microwave vacuum drying chamber should also ensure that the microwave field uniformity, and avoid the overheating of the material medium due in part to the field strength strong, while the other part is due to the weak electric field and heat, the structure of the microwave vacuum drying chamber should also meet the pressure vessel design requirements and specifications.Based on the above design principles, to determine the structure and size parameters of the microwave vacuum drying chamber. (2) microwave vacuum seal structure of microwave vacuum drying equipment connections, both microwave and vacuum double-sealed, microwave leakage control in the safety standards within the vacuum level should also achieve the design requirements. Therefore, the microwave vacuum drying chamber and the feed device interface, the flange and the expected out, etc., it is necessary to a suitable microwave sealing material to prevent microwave leakage, while also using the rubber ring is vacuum sealed to prevent system leakage causing the reduction of the vacuum. Conductive rubber, conductive metal ring and soft ferrite materials such as microwave sealing material according to the junction of the different structure type, respectively. (3) continuous access to material structure for access to material structure to ensure the continuous production, due to the frequent movement access to materials, the structure need to have a good seal to keep the vacuum degree of the whole system and to prevent microwave leakage, so The seal is key to the parts. Vacuum out of the material structure of rotating closed wind device structure, the structure of continuous conveying the good uniform feed, but it is easy sealing, to seal badly worn seal wear causes the vacuum system leak, causing the vacuum instability . At the same time, the gap in the microwave along the seals wear out radiation over radiation safety standards, resulting in the microwave leakage. In this study, the double flapper valve structure of the material from the hopper into the microwave drying chamber, the discharge from the chamber to the atmospheric environment.
Two main components designed 2.1 microwave vacuum drying chamber microwave vacuum drying chamber using a cylindrical cavity, the magnetic field lines of the cylindrical heater is more concentrated material to heat up faster, more suitable for dry material extruded rapid warming requirements, while the cylindrical structure is easy to meet the pressure container design requirements. By the workload, the maximum allowable temperature, vacuum degree of the work and the air breakdown field strength and pressure relationship, determine the maximum safe working electric field strength using the following formula can calculate the work load of the maximum power dissipation density. Microwave power of the unit of drying chamber should be less than the work load of the maximum power dissipation density, which can calculate the minimum volume of the drying chamber, the formula to determine the minimum volume of the drying chamber, and to consider the material coefficient, power density and the microwave field uniformity, and other factors to determine the main parameters of the drying chamber. In the case of constant input power, the larger the size of the cavity mode appears, the more electric field superposition of different modes, making a total of superposition of electric field is uniform in the entire cavity of the body. Another important parameter of the drying chamber is the quality factor, quality factor, said the quality of the resonator, the higher its value, the higher the microwave efficiency of utilization of the 2.2 microwave system Microwave system uses multi-fed mouth independent input of microwave energy to the drying chamber to reduce the The fed can be coupled power density of the mouth to prevent gas breakdown and arc discharge phenomena, each independent microwave sources include microwave power and microwave transmission systems. Microwave power source electrical circuit shown in Figure 2, in which key components magnetron VE, the system uses a continuous wave magnetron, magnetron working properly required voltage provided by dedicated microwave with a high leakage inductance of transformer T, in the 220V AC voltage on the primary winding of the transformer, the secondary low voltage winding for magnetron cathode heating filament voltage at the same time, the secondary high voltage winding kV class high voltage alternating current through the high voltage capacitor C voltage doubler rectifier circuit is composed of high-voltage diode VD, added to the magnetron between the two poles, a negative high voltage for the magnetron cathode. Magnetron work will be distributed a lot of heat, cooling control, easy to use, usually with forced air cooling, and the upcoming fan installed in the magnetron near the heat sink for cooling the work of the magnetron. The microwave transmission system is the magnetron output standard waveguide microwave power to the lowest loss transmission of microwave vacuum drying chamber, the magnetron output antenna plug into a standard waveguide broadside on the hole in the head attached to ensure that its output antenna uniform wire mesh gasket with the flange of the waveguide hole flange contact and then tighten the fixing screws, you can use [4]. Waveguide and the drying chamber junctions Falan Jia a Teflon plate, can block the water vapor in the drying process, the groove of the flange into the rubber ring seal vacuum, vacuum drying chamber environment. The use of soft ferrite ring to prevent microwave leakage.