RU2751423C1 - Method for ultrasonic drying of bulk materials - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to the field of drying various materials using ultrasonic vibrations. The method of ultrasonic drying of bulk materials involves the placement of bulk material in at least one cylindrical technological drum, pouring it during the rotation of the drum, exposure to ultrasonic vibrations using a disk-shaped emitter installed in front of one of the end walls of the drum so that the axis of rotation of the drum coincides with acoustic axis of the emitter. Ultrasonic action is carried out simultaneously on the material to be dried, placed on the inner and outer surfaces of several cylindrical drums rotating synchronously at the same speed, all drums on the side opposite to the emitter have a common end wall located at a distance that is a multiple of half the wavelength of the ultrasonic vibrations used in the gas medium, on the inner side of the drum of maximum diameter, as well as on the outer and inner surfaces of each subsequent drum, along each of its cylindrical generatrix, blades are made that ensure, when the drum rotates, the material is retained on the cylindrical surfaces when the blades move upward, and the material is poured out when the blades move down , in each of the drums, - except for the drum of the maximum diameter, - longitudinal grooves are made, ensuring the possibility of pouring material from each outer drum into the inner one when the groove moves up and for pouring out the material from each inner drum to the outer one by moving the groove down.

EFFECT: invention provides increased productivity and quality of the final product by ensuring uniform distribution of bulk material and effective ultrasonic action inside the drum dryer.

1 cl, 6 dwg

Description

The invention relates to the field of drying, in particular to methods of increasing the efficiency (process productivity and quality of the final product) of drying in drum-type devices using ultrasonic vibrations with a high level of sound force (intensity of ultrasonic exposure).

The invention can be used to create a modern material and technical base in the fields of industry and agriculture, where one of the technological stages is the drying of bulk materials and this process is implemented in drum-type devices.

The drying process, which consists in removing moisture from the material, on the one hand, is one of the key stages of various technological processes, and on the other hand, one of the most costly stages of product processing. The efficiency of the drying method largely determines the quality and cost of the final product. In this regard, drying methods are continuously being improved in the direction of intensifying (accelerating) the process while improving the quality of the resulting product.

To intensify the process of removing moisture from bulk materials, the most effective methods are based on the use of high-intensity ultrasonic vibrations.

Such methods are characterized by a number of specific features.

1. Acceleration of the drying process occurs only at high intensities of exposure. In the case of exposure of materials to vibrations with a low level of sound strength (less than 130 dB), the drying process is no different from convective drying, that is, there is a "critical" level of exposure at which the influence of ultrasonic vibrations is decisive and a process begins that can called acoustic (ultrasonic) drying.

2. Most of the experimental works indicate a nonlinear dependence of the intensity of drying on the magnitude of the level of the force of ultrasonic action. It was found that, starting from the intensity of acoustic vibrations of 140-160 dB, the process of moisture removal proceeds according to an exponential law.

Until now, it was considered that the most effective methods of ultrasonic drying are based on the use of vibrations created with the help of gas-jet transducers, which provide the formation of acoustic (ultrasonic) vibrations of high intensity in a gaseous medium. Therefore, a large number of ultrasonic drying methods have been proposed (Acoustic thermal method for drying materials, patent 2215953 RF: IPC F26B 5/02 (2000.01) / F26B 7/00 (2000.01) / Glaznev V.N.; patent holder: Glaznev Vladimir Nikolaevich; application: 2001122696 / 06 from 10.08.2001. Published: 10.05.2003) [1].

(Method for drying fibrous materials, patent 2171959 RF: IPC F26B 5/02 (2000.01) / F26B 7/00 (2000.01) / Izgorodin A.K., Senchenkov E.V., Semikin A.P .; patentee: Ivanovo State Textile Academy; Application: 99105625/06 from 18.03.1999. Published: 10.08.2001) [2], based on the use of gas-jet converters.

The most effective methods of drying are (Method of acoustic drying of capillary-porous materials, patent 2062416 RF: IPC F26B 5/02 (1996.01) / Glaznev V.N., Glinsky A.B .; patent holder: Institute of Theoretical and Applied Mechanics SB RAS; application : 94 94027716 of 22.07.1994. Published: 20.06.1996) [3], (Method for high-intensity acoustic drying of capillary-porous materials and a device for its implementation: RF patent 2548696: IPC F26B 5/02 (2006.01) / Koretsky S.L. .; Koretskiy V.A .; patentee: Limited Liability Company "Acoustic drying technologies" (RU); application 2013152695/06 dated 28.11.2013. Published: 20.04.2015) [4] a converter when supplying compressed air through it to the volume, converting the energy of the gas flow into the energy of elastic vibrations. The material to be dried is placed in a drying chamber, the size of which exceeds the volume of the material to be dried.

Such methods make it possible to accelerate the drying of materials due to exposure to vibrations, however, they have the following disadvantages:

- low drying efficiency, due to the fact that in practice a slight excess of the "critical" sound pressure level is ensured, which leads to a long drying time;

- the impossibility of increasing the efficiency of drying due to the need to increase the level of sound pressure above the level of "critical" pressure, since this requires an increase in the pressure of the gas supplied to the gas-jet radiator and an increase in the diameter of the nozzle hole. At the same time, the costs of creating compressed air increase and the operating frequency of the emitters decreases, which requires the complication of acoustic protection systems against negative effects on humans and the surrounding natural world (animals and plants). To simplify the protection systems, the dryers are made in the form of parallelepipeds, which eliminates the possibility of increasing efficiency due to pouring material in a rotating drum and reduces the efficiency of using vibration energy.

- gas-jet emitters work in the field of acoustic vibrations of sound frequency, which leads to the possibility of a negative impact on humans and the surrounding animal world. The efficiency of the gas-jet emitter significantly decreases upon transition to the region of ultrasonic vibrations. Thus, a gas-jet emitter with an operating frequency of 20 kHz should have a resonator and nozzle opening of about 1 mm, which significantly limits the gas flow used for conversion into acoustic vibrations. For this reason, the power of the generated vibrations cannot be more than 10 ... 100 W and the effectiveness of such an effect at the ultrasonic frequency becomes insufficient to ensure the effect of acoustic drying in real volumes.

To eliminate the disadvantages of the known drying methods associated with the use of exposure to sound frequencies (up to 15 kHz) and the implementation of drying methods at an ultrasonic frequency (more than 20 kHz), ultrasonic drying methods are proposed, for example (Method for drying capillary-porous materials, patent 2239137 RF: IPC F26B 5/02 (2000.01) / F26B 7/00 (2000.01) / Khmelev V.N., Zaborovsky A.N .; patent holder: State educational institution of higher professional education "Altai State Technical University named after II Polzunov" (AltSTU); application: 2003102919/06 from 31.01.2003. Published: 27.10.2004) [5]. When implementing such drying methods, metal discs are used as a source of ultrasonic vibrations (emitter), performing bending vibrations, excited by piezoelectric transducers (Ultrasonic vibrating system for gaseous media, patent 132000 RF MPK V06V 1/00 (2006.01) / Khmelev V.N. ., Galakhov A.N., Shalunov A.V., Nesterov V.A., Golykh R.N .; applicant and patentee: Limited Liability Company "Center for Ultrasonic Technologies AltSTU"; application No. 2013123940/28 dated 24.05.2013 . Published: 10.09.2013) [6].

The closest in technical essence to the proposed technical solution is a method of ultrasonic drying of bulk materials according to the patent (patent 2277611 RF) [7], taken as a prototype, and consisting in the fact that the material to be dried is placed in a cylindrical technological drum, it is poured during rotation drum, the effect of ultrasonic vibrations is carried out using a disk-shaped emitter installed in front of one of the end walls of the drum so that the axis of rotation of the drum coincides with the acoustic axis of the emitter.

This method is suitable for drying various bulk materials.

As a source of ultrasonic vibrations, a disc radiator is used, made of metal, performing bending vibrations excited by a piezoelectric transducer. Drying is carried out in a drum-type installation and consists in continuous energetic action of elastic vibrations of ultrasonic frequency on the material being poured during the rotation of the drum and pouring the material to be dried inside it. The use of ultrasonic vibrations to influence the material to be dried reduces the requirements for the protection of personnel serving the dryer, reduces material consumption (the possibility of using thin metal walls in the drum is ensured), and the use of disk emitters with an efficiency of more than 40 ... 50% can significantly reduce energy consumption for the formation of ultrasonic exposure ...

At the same time, the method of ultrasonic drying of bulk materials according to (Method of ultrasonic drying of linen in drum-type washing machines, patent 2277611 RF IPC D06F 58/02 (2006.01) / Khmelev V.N., Tsyganok S.N., Zaborovsky A.N., Barsukov R.V., Savin I.I., Shalunov A.V., Khmelev M.V .; patent holder State educational institution of higher professional education "Altai State Technical University named after II Polzunov" (Altai State Technical University); application 2004133804 / 12 from 18.11.2004. Published: 10.06.2006) [7] the following disadvantages are inherent.

1. The drying method adopted as a prototype has limitations associated with the amount (weight) of a one-time dried bulk material. This is due to the limitation of the size of the drum of the dryer and the need to place only such an amount of dried material at the bottom of the drum, which, being poured during the rotation of the drum, creates the maximum possible surface of action on the material. Theoretically, the limiting volume of the material to be dried cannot be more than half of the drum volume, but practically does not exceed 25%.

2. The effectiveness of the method is limited by the impossibility of uniform distribution of the material to be dried over the volume of the drum during its rotation. Most of the material is always in the down position, creating a thick layer of material. In this layer, only the surface layer is dried, i.e. only a small part of the material to be dried is exposed. This increases the drying time and does not allow the benefits of ultrasonic drying to be fully realized.

3. When turning the drum, uniform distribution of bulk material over the section of the drum is not realized, large masses of material are poured, which leads to partial destruction of particles, granules or grains of the material to be dried.

4. The method does not allow for effective use of ultrasonic radiation from a disk emitter, since the effect in the chamber depends significantly on the amount of material in the drum, and its location changes during pouring. In this case, resonant conditions for amplifying vibrations due to reflection from the rear wall of the drum can arise or be adjusted by hardware only at certain moments of the process, for example, when all the material is at the bottom of the drum.

The listed disadvantages limit the capabilities of the known method of ultrasonic drying, lead to a significant decrease in the productivity of the technological operation of drying and loss of quality of the final product, which makes this drying method economically beneficial only for drying especially valuable and expensive materials with continuous stirring of small volumes (amount) of the material to be dried to ensure uniformity of drying.

The proposed technical solution is aimed at eliminating the disadvantages of the existing method of ultrasonic drying of bulk materials, and creating a new method for ultrasonic drying of bulk materials, capable of increasing the productivity of drying operations and increasing the quality of the final product by ensuring uniform distribution of bulk material and effective ultrasonic action inside the drum dryer.

In addition, the proposed drying method will increase the attractiveness of the ultrasonic drying method itself, reduce the cost of the process, and will create mobile small dryers.

The essence of the proposed technical solution lies in the fact that in the known method of ultrasonic drying of bulk materials, which involves the placement of bulk material in at least one cylindrical technological drum, pouring it during the rotation of the drum, exposure to ultrasonic vibrations using a disk-shaped emitter installed in front of one from the end walls of the drum so that the axis of rotation of the drum coincides with the acoustic axis of the emitter, ultrasonic action is carried out simultaneously on the material to be dried, placed on the inner and outer surfaces of several cylindrical drums rotating synchronously at the same speed. All drums on the side opposite to the radiator have a common end wall located at a distance that is a multiple of half the wavelength of the ultrasonic vibrations used in a gas environment, on the inner side of the drum of maximum diameter, as well as on the outer and inner surfaces of each subsequent drum, along each of its cylindrical generatrix, blades are made that ensure, when the drum rotates, the material is retained on cylindrical surfaces when the blades move upward, and the material spills out when the blades move downward, in each of the drums, except for the drum of maximum diameter, longitudinal grooves are made, the width of which is selected from the condition of ensuring the possibility pouring material from each outer drum into the inner one when moving the groove up and for pouring material from each inner drum into the outer one when moving the groove down. Ultrasonic action on the material to be dried is carried out continuously at a frequency of 20 to 25 kHz with a level of ultrasound power in the range of 146 ... 160 dB when the drums rotate, pouring the material, sequentially, from the inner surface of the outer drum to the outer surface of the next drum inside it, and then from the outer surface of this drum, successively, on its inner surface and the outer surface of the next drum of a smaller diameter.

Thus, in the proposed technical solution, the task of increasing the productivity of the drying operation and improving the quality of the final product is achieved by ensuring uniform distribution of bulk material and effective ultrasonic action on the material.

This is achieved by the fact that the ultrasonic action is carried out simultaneously on the bulk material, placed on the inner and outer surfaces of several cylindrical drums, axisymmetrically located relative to the acoustic axis of the disk radiator and rotating synchronously at the same speed.

Resonant amplification of ultrasonic vibrations in the dryer is achieved due to the fact that all drums on the side opposite to the emitter have a common end wall located at a distance that is a multiple of half the wavelength of the ultrasonic vibrations used in a gaseous medium.

Uniform distribution of the increased amount of material to be dried is ensured due to the fact that on the inner side of the drum of maximum diameter, as well as on the outer and inner surfaces of each subsequent drum along its entire cylindrical generatrix, blades are made, which ensure, when the drum rotates, the material is retained on the cylindrical surfaces when the blades move up and material spillage when the blades move downward.

To ensure uniformity of drying, by ensuring optimal distribution of material in the drums and continuous pouring of small amounts of material throughout the volume of the dryer, in each of the drums, in addition to the drum of maximum diameter, longitudinal grooves are made, the width of which is selected so that material can be poured from each external drum into the inner one when the groove moves up and for pouring material from each inner drum into the outer one when the groove moves down.

To ensure the maximum efficiency of drying bulk materials in small volumes (thin layers), ultrasonic action is carried out in the inaudible and imperceptible frequency range from 20 to 25 kHz with the level of ultrasound power in the range of 146 ... 160 dB. When exposed to such a level of ultrasound force, moisture is removed from the surface of the particles of the material to be dried at maximum speed due to mechanical ultrasonic spraying (i.e., without phase transfer of the liquid to a vapor state) and moisture is released from the depths of the particles (grains, granules) of the material to be dried. The limitation of the level of ultrasound power to 160 dB is due to the fact that a further increase requires a disproportionately large increase in electrical energy to generate vibrations with such an intensity. In addition, the specified value of the level of ultrasound power of 160 dB requires the operation of the emitter with such a level of amplitudes of mechanical vibrations (more than 100 microns), at which the emitter is destroyed.

The maximum speed and uniformity of drying with minimal destruction of the particles of the material to be dried is ensured due to the fact that the ultrasonic effect is carried out evenly over the entire volume of the material, distributed in thin layers and poured in small portions when the drums rotate, moving the material, sequentially, from the inner surface of the outer drum to the outer surface located inside it of the next drum, and then from the outer surface of this drum, sequentially, to its inner surface and the outer surface of the next drum of a smaller diameter.

The essence of the technical solution is illustrated in FIG. 1-6, which schematically show the cross-sections of the drums of the drying chamber during their rotation.

For ease of understanding the essence of the method, consider the drying process using the example of a dryer containing a housing 1 and two inner cylinders 2 and 3 with blades 4 located at an angle of 60 ° relative to each other around the circumference.

The method is implemented in a drum-type dryer. The dryer is a cylindrical drum 1, which is the body of the installation with a diameter equal to the diameter of the disk ultrasonic emitter (not shown in the figures). The ultrasonic emitter is installed in the end wall of the housing. Inside the body, coaxially with it, there are cylindrical drums of a smaller diameter, then there are cylinders. On the inner surfaces of all cylinders and the body, along their generatrices, blades 4 are placed, on the outer surfaces of all cylinders, also, along the generatrices, double-sided blades are placed, the shape and number of which is selected according to the properties of the material to be dried. Each cylinder has a longitudinal groove 5, the width of which is selected based on the properties of the material.

The proposed method for ultrasonic drying of bulk materials is implemented as follows. Drying bulk material 6 is poured into the drying unit through the technological opening, and the volume of the material is 15-25% of the volume of the body.

Then the drying unit is started to rotate with an electric motor (not shown in the figures) with a frequency of 5-10 rpm, depending on the moisture content and flowability of the material. Simultaneously with the rotation, ultrasonic action is carried out by a source of powerful ultrasonic vibrations of 146-160 dB.

In the initial position (Fig. 1), the bulk material is located in the lower parts of the cylinders and the housing. As the drum begins to rotate, the blades pick up the material and hold it on the inner surfaces of the cylinders and housing.

When the drying drum is rotated at an angle of about 60 degrees (Fig. 2), the material begins to pour onto the outer side of the cylinders of smaller diameters, where the material is held by the blades of these surfaces.

At an angle of about 120 degrees (Fig. 3), in addition to the above described operation, material is poured from the small cylinder through the groove into the large cylinder.

Further rotation of the drum leads to the pouring of material from the large cylinder through the groove into the inner part of the drum body (Fig. 4).

When the drum is rotated at an angle of about 240 degrees (Fig. 5), material does not flow through the grooves.

At an angle of about 300 degrees (Fig. 6), the material from the outer surface of the small cylinder is poured into its inner volume, the same process occurs with the material on the large cylinder at an angle of about 380 degrees (not shown in the figure).

Thus, the proposed drying method allows you to evenly distribute bulk material in the volume of the drying drum, which leads to a uniform sounding of the material.

The length of the drum dryer allows to accommodate sufficient volumes of bulk material (about 3 m) and is limited by the power of the ultrasonic emitter.

The ultrasonic dryer according to the proposed method has the following technical characteristics: the diameter of the emitter and the drying chamber is 380 mm; length 1 m, material of the walls of the drying chamber - metal; the maximum load of the drying chamber is 25 kg.

To determine the effectiveness of the developed and proposed ultrasonic dryer, experimental studies were carried out in a specially designated room, in which a disk radiator with a consumed electric power of 350 W was used. The temperature in the drying chamber was maintained at 80-90 ° C, the ambient humidity was 20-23%.

When determining the functionality of the ultrasonic dryer, a series of experiments was carried out on two different substances: peas and polymer granules.

Based on the analysis of the results of experiments on drying substances only by heat exposure and drying using ultrasonic exposure with simultaneous thermal exposure in the process of drying dry peas and polymer granules, it was found that drying using ultrasonic exposure is 2 ... 2.5 times faster than drying without ultrasonic exposure. The results obtained confirmed the effectiveness of the proposed method for ultrasonic drying of various materials.

The ultrasonic drying method can be used both independently and as part of technological lines for drying various materials.

A device that implements the proposed method is being prepared for industrial use.

Claims (1)

A method of ultrasonic drying of bulk materials, involving the placement of bulk material in at least one cylindrical technological drum , pouring it during the rotation of the drum, exposure to ultrasonic vibrations using a disk-shaped emitter installed in front of one of the end walls of the drum so that the axis of rotation of the drum coincides with acoustic axis of the radiator, characterized in that the ultrasonic treatment is performed simultaneously on the material to be dried, placed on internal and external surfaces of a plurality of cylindrical drums which rotate synchronously with the same velocity, all the drums on the side opposite the emitter have a common end wall, spaced, fold half the wavelength of the ultrasonic vibrations used in a gas environment, on the inner side of the drum of maximum diameter, as well as on the outer and inner surfaces of each subsequent drum, along each of its cylindrical which generatrix, blades are made that ensure, when the drum rotates, the material is retained on cylindrical surfaces when the blades move upward, and material spills out when the blades move downward, in each of the drums, except for the drum of maximum diameter, longitudinal grooves are made, the width of which is selected from the condition of ensuring the possibility of pouring material from each outer drum into the inner one when moving the groove upward and for pouring out the material from each inner drum into the outer one - when moving the groove downward, the ultrasonic effect on the material being dried is carried out continuously at a frequency of 20 to 25 kHz with a level of ultrasound power within 146 ... 160 dB when the drums rotate, pouring the material, sequentially, from the inner surface of the outer drum to the outer surface of the next drum inside it, and then from the outer surface of this drum, sequentially, to its inner surface and the outer surface of the next drum ana of a smaller diameter.

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