RU2741359C1 - Device for induction heating of contact drying drum - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to drying liquid pastes, concentrates and may be used in dairy, food and chemical industries. Device for induction heating of contact drying drum includes hollow cylindrical heating drum, reducing gear, electric motor, power supply unit, inductor arranged inside the heating drum casing and cooling element. Cooling element used is fan installed at drum end face and directed towards inductor. Device comprises a temperature sensor which is in contact with an inductor and transmits a temperature value to the control panel to monitor operation of the inductor, microcontroller, controlling the whole process and providing data exchange with control panel, control of fan, voltage regulator, engine rpm, generating PWM signal to driver and power IGBT module, feedback unit transmitting feedback from inductor and heated drum to microcontroller, and to which are output data of current transformer, installed in series with inductor and temperature sensors, tray for dried material, knife for removal of dried product from drum surface. Distance in radial direction between inner surface of hollow cylindrical drum and outer surface of inductor is set within 3-8 mm, inductor is litzendrat uniformly distributed on non-conductive frame along inner part of drum, with number of turns from 8 to 24, located at minimum distance between each other, width of inductor makes third part of internal surface area of drum, inductor is located so that it heats drum segment, generated induction current on surface of inductor increases due to perpendicular arrangement of concentrators relative to inductor.EFFECT: device has simplified design, and drum with induction heater is more efficient in use.1 cl, 2 dwg

Description

The present invention relates to a method for drying liquid pastes, concentrates and can be used in the dairy, food, and chemical industries.

There are spray drying methods, an important disadvantage of which is the high cost of equipment when it is necessary to obtain a dry product in a small volume. Another process used so far is the contact drying method on the surface of a steam heated drum, which is also disadvantageous in low tonnage production due to the high cost of equipment in relation to productivity and the high cost of generating steam. The optimal ratio of productivity to cost can be achieved by using the proposed technical solution, which has a relatively low cost and does not require steam for its operation.

The drum with an induction heater used in the present invention has many advantages over the drying drum proposed in RF patent 2020392. First, since no steam is used to heat the drum, the disadvantages inherent in a steam-heated drum are eliminated. Namely, the walls of the drum do not have to be thick-walled since there is no need to withstand high steam pressure. Thus, material savings are achieved. Moreover, this drum is much lighter and easier to handle than previous steam-heated drums. The power required to drive it and the load requirements on the bearings are not as high as in steam-heated dryers. In addition, this drum heats up faster, since it takes much less time to heat up by induction currents than to build up steam pressure in a boiler. In addition, a drum with an induction heater is more economical to use, because heating occurs at the direct contact point between the inside of the drum and the induction heater, because the distance between the heating elements and the drum surface is relatively small.

Known is the closest technical solution JP3556287B2, including a roller induction heating device having a rotating drum shell and an induction heating mechanism including an iron core and induction coils wound on an iron core. The disadvantages of this technical solution are: the use of several induction coils, the presence of liquid cooling, which complicates the design of the induction dryer, the use of lead electrical contacts excludes the use in the food industry.

The object of this invention is to provide an economical device with a simplified design for drying using a drum heated by induction currents.

The technical result from the use of the proposed device is to simplify the design of the induction dryer, while overheating the surface of the inductor from the heated drum is excluded.

To solve this problem, a device for induction heating of a contact drying drum is proposed, which contains a hollow cylindrical heating drum, a reduction gear, an electric motor, a power supply, an inductor located inside the housing of the heating drum, and a cooling element. A fan installed at the end of the drum and directed towards the inductor is used as a cooling element. The device contains a temperature detection sensor, which is in contact with the inductor and transmits the temperature value to the control panel to control the operation of the inductor, a microcontroller that controls the entire process and provides data exchange with the control panel, fan control, voltage regulator, engine speed, and generates a PWM signal to driver and power IGBT module, a feedback unit that transmits feedback from the inductor and the heated drum to the microcontroller, and to which the data of the current transformer is output, installed in series with the inductor and temperature sensors, a bath for the material to be dried, a knife for removing the product to be dried from the drum surface ... The distance in the radial direction between the inner surface of the hollow cylindrical drum and the outer surface of the inductor is set within 3-8 mm, the inductor is a litsedrat, evenly distributed on the non-conductive frame along the inner part of the drum with the number of turns from 8 to 24, located at a minimum distance between themselves, the width of the inductor is one third of the inner surface area of the drum, the inductor is located so that it heats the drum segment, the generated induction current on the surface of the inductor increases due to the perpendicular arrangement of the concentrators with respect to the inductor.

FIG. 1 shows a block diagram of an induction heating device for a contact drying drum, where

1 - control panel,

2 - microcontroller,

3 - feedback block,

4 - driver,

5 - voltage regulator,

6 - power supply,

7 - inductor cooling fan,

8 - power IGBT module,

9 - inductor,

10, 11 - temperature sensors,

12 - current transformer (alarm indicator),

13 - heating drum of contact drying,

14 - electric motor,

15 - reduction gear.

FIG. 2 shows a diagram of a drum of contact drying, where

16 - tray for the material to be dried,

17 - knife.

Induction heating is an electromagnetic heating technology that has several advantages such as high security, scalability, and high energy efficiency. Induction heating is currently used in metalworking and medicine. However, the application of this technology in the food industry is still at an early stage. Although there are many patents on the use of induction heating for processing food materials, there is still a need for more scientific and technical solutions that increase the productivity and energy efficiency of induction heating technology applied in various unit operations such as drying, pasteurization, sterilization and roasting in food processing. This is necessary to optimize various design and operating parameters such as the current frequency applied, the type of materials used, the size and configuration of the equipment, and the coil configuration.

The technical solution we offer is a hollow drum (13) fixed to the frame with bearings, which is driven through a gearbox (15) by an electric motor (14). The magnetic flux inductor (9) is located inside the rotating drum body (13) and thereby heats the drum segment using the induction current.

To prevent the possibility of a short circuit and damage to the induction coil, to simplify the design (exclude liquid cooling) and reduce the drum heating time, the distance in the radial direction between the inner surface of the hollow cylindrical drum body and the outer surface of the inductor (induction coil) is set within 3-8 mm.

When the radial distance between the outer surface of the inductor (9) and the inner surface of the hollow heating drum (13) is less than 3 mm, the adverse effect of heat radiation on the inductor from the hollow drum needs to be prevented by additional air cooling. When the distance is more than 8 mm, then the efficiency of thermal action on the induction coil is minimal, but the power of the magnetic field directed to the surface of the hollow drum decreases.

Power is supplied to the inductor (9) from an external power source using a contact wire. The fan (7) is installed at the end of the drum and is directed towards the inductor (9).

The temperature sensor (thermocouple) (11) is in contact with the inductor (9). The temperature value is transmitted to the control panel (1) to control the operation of the inductor.

The proposed technical solution, which makes it possible to exclude overheating of the inductor surface from the heated drum and maximally concentrate the variable induction field on the inner surface of the drum, consists in a certain shape of the inductor.

The working inductor is litz wire, evenly distributed on a non-conductive frame along the inner part of the drum, with the number of turns from 8 to 24. This solution eliminates the need for liquid cooling of the inductor. The maximum concentration of the alternating magnetic field on the surface of the inductor is achieved through the use of special concentrators of the magnetic field, consisting of carbonyl and oxide iron. The width of the inductor with a plurality of turns located at a minimum distance from each other is one third of the inner surface area of the drum. The generated induction current on the inductor surface is increased due to the perpendicular arrangement of the concentrators in relation to the inductor.

The microcontroller (2) controls the entire process and communicates with the control panel (1) (buttons and display), controls the fan (7) and voltage regulator (5), receives feedback from the inductor (9) and the heated drum (13) through the unit feedback (3) and generates a PWM signal to the driver (4) and the IGBT half-bridge (8).

A 15 volt power supply (6) for powering the IGBT driver, fan, relays and feedback circuits, and 5 volts are needed to power the rest of the microcircuits, including the microcontroller.

The feedback unit (3) displays data from the current transformer (12) installed in series with the inductor and temperature sensors (10, 11) (inductor, heating drum, material to be dried).

The outer side of the drum (13) is supported by bearings on the frame and is driven through a gearbox (15) by an electric motor (14).

The rotation speed of the drum (13) is changed (in the range from 0 to 10 rpm) by changing the rotation speed of the engine (14), which is controlled by the microcontroller (2).

The heated drum, inductor, power module form a resonant oscillatory LC circuit with a constant resonant frequency. The amplitude of the meander supplied to the inductor is formed by the value of the voltage applied to the upper arm of the IGBT half-bridge (8). By changing the voltage (in our case 175-325 volts), we change the intensity of the drum heating.

Because the microcontroller generates a PWM signal to the half-bridge driver, we can program it for several operating protocols on the principle of modulating the signal density (the resonant frequency is known and unchanged). By skipping part of the pulses that open the power switches of the IGBT (if we skip every second signal, we get 50% of the power). Further, choosing the working protocol, we change the drum heating rate.

The inductor heats up the drum segment in the most cooled part (in the area where the material to be dried is fed to the drum). Knowing the temperature of the material to be dried, its moisture content, the speed of the drum, we can, by changing the intensity and speed of heating the drum, go to the required temperature mode of operation of the device (uniform heating of the drum around the perimeter and the required moisture content of the material being dried while removing it from the drum with a knife).

The proposed device for induction heating of the drum of contact drying does not require time to warm up the surface of the drum, in contrast to resistive and infrared heating. The efficiency of this heating method is about 90%, in contrast to 60-70% from other methods. The main feature is that induction heating is carried out only at the resonant frequency. The resonance parameters are set by the inductance and capacitance of the installation itself. Feedback is carried out using temperature sensors that control the drum heating temperature. The change in the intensity of the induction effect is carried out by changing the density of the signal supplied to the inductor and changing the power of the signal supplied to the power section.

Example

Whole milk 3 - 6% fat after pasteurization, heated to 60 ° C, is fed into the tray for the material to be dried (16). The drum (13), fixed to the frame by means of bearings, is driven through the gearbox (15) by an electric motor (14) at a preset speed of 3 rpm, set on the control panel (1). The heated drum (13), the inductor (9), the power module (8) form a resonant oscillatory LC circuit with a constant resonant frequency. The power supplied to the inductor (9) for drying whole milk is set on the control panel (1) to 50%, which is 1.2 kW. The inductor (9) induces eddy currents in the drum (13), which, due to the Joule heat, heats the drum segment in the zone of contact with the material to be dried. When the drum rotates after contact with milk, a uniform film of the dried product is formed. The temperature of the film formed on the drum is 92 ° C. Intense steam release occurs. The product to be dried applied to the cylindrical surface of the drum is removed with a knife (17). The moisture content of the dry product on the removal knife (17) from the drum is 5-7%.

Due to the fact that the design of the device does not imply liquid cooling, the inductor consists of one induction coil, the proposed device has a simplified design compared to its closest analogue. In addition, a drum with an induction heater is more economical to use, because heating occurs at the direct contact point between the inside of the drum and the induction heater, which is an advantage over steam and spray methods. The proposed drum drying device does not require time to warm up the drum surface, in contrast to resistive and infrared heating. Overheating of the surface of the inductor from the heated drum is excluded due to the shape of the inductor and the set radial distance between the inner surface of the drum body and the outer surface of the inductor (3-8 mm).

Claims (1)

A device for induction heating of a drum of contact drying, containing a hollow cylindrical heating drum, a reduction gear, an electric motor, a power supply, an inductor located inside the body of the heating drum, a cooling element, characterized in that a fan installed at the end of the drum and directed to side of the inductor, the device contains a temperature sensor, which is in contact with the inductor and transmits the temperature value to the control panel to control the operation of the inductor, a microcontroller that controls the whole process and provides data exchange with the control panel, fan control, voltage regulator, speed of rotation of the motor generating PWM signal to the driver and power IGBT module, a feedback block that transmits feedback from the inductor and the heated drum to the microcontroller, and to which the data of the current transformer installed in series is output with an inductor and temperature sensors, a bath for the material to be dried, a knife for removing the product to be dried from the surface of the drum, the distance in the radial direction between the inner surface of the hollow cylindrical drum and the outer surface of the inductor is set within 3-8 mm, the inductor is a litz wire evenly distributed over the non-conductive frame along the inner part of the drum with the number of turns from 8 to 24, located at a minimum distance between themselves, the width of the inductor is one third of the inner surface area of the drum, the inductor is located so that it heats the drum segment, the generated induction current on the inductor surface increases due to the perpendicular arrangement concentrators in relation to the inductor.

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