RU2737381C1 - Device for microwave drying of various materials in thin layer - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: device is intended for drying of various materials in thin layer by super-high frequency (SHF) electromagnetic field and allows drying both bulk materials of technical purpose, and agricultural and food products. Device for SHF drying of different materials in thin layer consists of multilevel conveyor system, having inlet device at loading, and at outlet of unloading device, microwave modules, each of which includes several microwave generators, assembled according to the scheme of power summation of magnetrons, fan units and SHF protection in the form of metal mesh, wherein microwave modules are located under multi-level conveyor system, distance from microwave modules emitters to upper belt of lower conveyor is equal to quarter wavelength of radiation (¼λ), and distance between upper belts of all conveyors is equal to or multiple to half of radiation wavelength (½λ).

EFFECT: reduction of weight and size characteristics as compared to existing devices for microwave drying, increase of SHF energy use factor and, as a result, reduction of power inputs per unit of dried product.

1 cl, 2 dwg

Description

The device is designed for drying various materials in a thin layer by an ultra-high-frequency (microwave) electromagnetic field and allows drying both bulk materials for technical purposes, as well as agricultural and food products. The technical field to which the invention relates.

The invention relates to a technology for drying a microwave electromagnetic field of various materials in a thin layer. The optimum layer thickness is from 1 to 15 mm, depending on the type and properties of the material to be dried. You can dry bulk materials for technical purposes: sawdust, fine coal, powders and much more. Also, the device allows you to dry agricultural and food products: cut fruits and vegetables, grain, herbs, and the like.

State of the art

The proposed device has low weight and size characteristics and provides more efficient use of microwave energy in comparison with existing conveyor-type microwave dryers. Such dryers are presented on the sites [http://materialdryer.ru ,. http://agroserver.ru/b/img/900915/l 111447 /]. In them, a thin layer of material located on a conveyor belt moves in an extended chamber, into which microwave power is supplied from several microwave generators located along the chamber. For example, in the patent [RF Patent, cl. Н05В 6/64 No. 2050704] (prototype) describes a 3-tier conveyor system in which the radiators of microwave generators are located almost close to each other, and the fields from them will intersect. This leads to a significant decrease in the total microwave power, since the generators in such devices are not synchronized. To avoid strong influence on each other, you have to place them at a sufficiently large distance from each other along the device [. http://agroserver.ru/b/img/900915/l 111447 /], and this leads to an increase in overall dimensions and, consequently, to an increase in the weight of the entire device. In addition, in such devices, the efficiency of using microwave power in the drying process is unknown, since a thin layer of material has a volume many times less than the volume of the chamber in which the microwave field is created, and it can absorb only part of the power of this field. Part of the energy of the microwave field not absorbed by the material goes to heating the elements of the device.

The technical result is a decrease in weight and size characteristics in comparison with existing devices for microwave drying, an increase in the utilization rate of microwave energy and, as a consequence, a decrease in energy consumption per unit of dried product.

The essence of the invention

In the proposed invention, modules are used as microwave generators that operate on the principle of coherent addition of the powers of generators on magnetrons to obtain the required total power [RF patent No. 2394357]. Microwave modules (1) are located under a multilevel conveyor system, each belt of which is at a given distance from the emitters of the modules (Fig. 1). The microwave field extends from the emitters vertically upward, and, passing through all layers of material on each tape, is absorbed by it until it is completely attenuated. The conveyor belts move synchronously with a speed that provides the required moisture content of the dried material at the exit.

λ), а расстояние между верхними лентами всех конвейеров равно или кратно половине длины волны излучения (

λ). Это связано с волновой природой распространения электромагнитного поля, максимумы которого приходятся на верхние ленты с располагаемым на них материалом, который будет нагреваться. Часть СВЧ поля поглотиться материалом на нижнем конвейере, прошедшая часть поля будет поглощаться в слоях материала на последующих конвейерах до полного затухания. При установившемся режиме работы устройства материал на нижнем конвейере будет иметь минимальную влажность и не сильно поглощать СВЧ поле, а максимум поглощения поля будет на верхнем конвейере на материале с исходной влажностью. В результате эффективность использования мощности СВЧ поля приближается к максимальному. Все конвейеры приводятся в движение от одного управляемого двигателя, синхронно движутся навстречу друг другу, и материал всегда будет перемещаться через максимумы СВЧ поля с одинаковой скоростью. Регулировкой скорости движения всего конвейера можно получать на выходе материал с требуемой влажностью.The device for microwave drying of various materials in a thin layer consists of a multilevel conveyor system and several microwave modules, the number of which is determined by the required performance of the device, and the number of magnetrons in one module is determined by the configuration of the device. Microwave modules are located under the conveyor system so that the microwave field from the emitters is directed vertically upward. The distance from the emitters to the upper belt of the lower conveyor is equal to a quarter of the radiation wavelength (

λ), and the distance between the upper belts of all conveyors is equal to or a multiple of half the radiation wavelength (

λ). This is due to the wave nature of the propagation of the electromagnetic field, the maxima of which fall on the upper ribbons with the material placed on them, which will be heated. Part of the microwave field will be absorbed by the material on the lower conveyor, the passed part of the field will be absorbed in the layers of material on subsequent conveyors until it is completely attenuated. In the steady state of operation of the device, the material on the lower conveyor will have a minimum moisture content and not strongly absorb the microwave field, and the maximum absorption of the field will be on the upper conveyor on the material with the initial moisture content. As a result, the efficiency of using the power of the microwave field approaches the maximum. All conveyors are driven by a single controlled motor, move synchronously towards each other, and the material will always move through the maxima of the microwave field at the same speed. By adjusting the speed of the entire conveyor, you can get the material with the required moisture at the exit.

Implementation of the invention

The device is a multilevel conveyor system consisting of several belt conveyors (4), located one above the other, as shown in the diagram (Fig. 1), and has a common drive (not shown in the diagram), which ensures synchronous movement of belts towards each other. On the diagram, arrows indicate the direction of movement of each tape. Material (5) at the entrance from the loading-loading hopper (2) is fed to the upper conveyor. Moving through the microwave field and heating up, the material is poured onto the lower conveyor and, passing through a more intense field in the opposite direction, heats up even more; and so on up to the device for unloading into the receiving hopper (3) at the exit. As a conveyor belt, propylene (or other material with a low microwave absorption coefficient) is used in the form of a mesh with a suitable mesh size, or a solid belt of the required thickness. On each side of the multilevel conveyor there are fan units (7), one of which pumps air and the other pulls it out (Fig. 2). Air removes moisture from the conveyor zone, leaving the material when heated, and cools the material surface and moving parts of the conveyors. Microwave modules with emitters (1) are located under the lower belt of the lower conveyor, forming the directivity diagram of the microwave field vertically upward. Each microwave module creates a vertical material heating zone on all conveyors. The distance between the microwave modules along the conveyor is selected from the condition of the minimum interaction of their microwave fields (must be at least one meter), and a sufficient degree of cooling of the dried material when moving from one heating zone to another. In the case of using magnetrons for household microwave ovens operating in the frequency range 2430 ÷ 2470 MHz, which corresponds to a wavelength of ~ 12 cm, the distance between the cuts of the emitters and the upper belt of the lower conveyor is 30 mm, and between the upper belts of all conveyors - 60 mm. Between the fan blocks and the device, as well as on its other sides, there is a metal mesh (6), which protects the surrounding space from an unused microwave field (Fig. 2). Fan blocks and microwave protection grid are designed to provide access to the device for its maintenance. From the control panel microwave modules, fan units, conveyor drive are switched on, and the conveyor speed is changed.

Claims (1)

A device for microwave drying of various materials in a thin layer, consisting of a multi-level conveyor system with a loading device at the input and an unloading device at the output, microwave modules, each of which includes several microwave generators assembled according to the scheme of adding the powers of magnetrons, fan blocks and Microwave protection in the form of a metal mesh, characterized in that the microwave modules are located under a multi-level conveyor system, the distance from the microwave modules emitters to the upper belt of the lower conveyor is equal to a quarter of the radiation wavelength (

λ), and the distance between the upper belts of all conveyors is equal to or a multiple of half the radiation wavelength (

λ).

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