RU2447926C2 - Method of coagulating foreign particles in gas flows - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention is intended for cleaning gases of suspended foreign particles released in production processes of mining, chemistry and heat power engineering. Proposed method consists in affecting particles by elastic vibrations focused into line rotating perpendicular to pipeline axis, line length complying with pipeline diameter. Elastic vibrations are generated by piezoelectric transducer vibrating in lengthwise direction and revolving along acoustic axis, and supplied by electronic generator. Elastic vibrations are radiated and focused by mechanical radiator acoustically coupled with said transducer and made up of rectangular plate with thickness varying in stepwise manner. Said plate performs bending vibrations relative to its larger axis at frequencies multiple of the main one, in the range of 30 KHz to 20 KHz. Not here that vibrations generated by both sides of said plate are focused simultaneously. Vibrations generated by radiator side reversed to flow of particles are directed thereto after reflection and passing the distance exceeding radiator lengthwise size by magnitude multiple of half the wavelength of ultrasound vibrations in air.

EFFECT: higher efficiency of ultrasound coagulation.

1 dwg

Description

The invention relates to the field of gas purification technology from suspended foreign particles due to exposure to them by high-intensity ultrasonic vibrations, and in particular to methods for coagulation of particles released during production in various industries (mining, metallurgy, chemical, heat and power, food) industries.

Due to the widespread occurrence of potentially hazardous industries, characterized by a high content of toxic solid and liquid substances in the exhaust gases, as well as the need to capture valuable materials from the gas medium in some cases, it becomes necessary to develop effective methods for coagulating particles in gas streams. The task is greatly complicated when it is necessary to capture chemically active and aggressive substances. In this case, the traditional means of trapping aerosols are not applicable. A possible solution to the existing technological problem is the enlargement and subsequent deposition of aerosol particles under the influence of high-intensity (more than 140 dB) ultrasonic vibrations (ultrasonic coagulation of aerosols) [1]. Ultrasonic (ultrasound) coagulation has a number of undeniable advantages:

- applicability to aggressive and explosive gases;

- the ability to work at high temperatures and pressures;

- high efficiency and low energy intensity of the process;

- the possibility of deposition of fine aerosols.

The vast majority of known [2-3] methods for ultrasonic coagulation of foreign particles in gas flows is characterized by the use of gas-jet acoustic emitters as elastic oscillators, which convert the energy of compressed gas into energy of ultrasonic vibrations. In this case, the known methods are characterized by low coagulation efficiency, which is due to the low efficiency of gas-jet emitters (less than 20 ... 25% depending on the used structural scheme), the need to use special compressors to create and supply compressed gas. In addition, when implementing the known methods (using gas-jet emitters), it is possible to ensure high radiation intensity (power) only at low operating frequencies (up to 10 kHz), since at ultrasonic frequencies (more than 20 kHz) the diameters of the output nozzles of the emitters and resonators become small ( less than 1 mm), which limits the values of the acoustic power of the generated oscillations to values not exceeding 1 ... 10 W [4]. For this reason, the implementation of coagulation methods using ultrasonic vibrations generated by gas-jet emitters becomes ineffective.

A significant drawback of the known coagulation methods is also the injection of a working gas stream into the coagulation region, which leads to re-entrainment of the deposited particles by the air flow, leading to the destruction of aggregates of coagulated particles, reducing also the coagulation efficiency. Known methods of cutting off air flows using soundproof films in [5] lead to a significant weakening of ultrasonic vibrations, and are also unacceptable at high temperatures and pressures.

The above disadvantages limit the possibilities of industrial application of ultrasonic coagulation of foreign particles in gas flows and necessitate the creation of new methods based on the more efficient creation and application of high-intensity ultrasonic vibrations.

Among the known methods for coagulation of particles in gas flows [2-3], the closest to the proposed technical solution and one of the most effective methods of coagulation using acoustic emitters (static and dynamic sirens, pneumatic horns, electromagnetic loudspeakers, etc.) is consisting in exposure to lens-focused vibrations [3], adopted as a prototype.

In the method of coagulation of foreign particles in gas streams adopted as a prototype, the particles are subjected to elastic vibrations. In order to increase the efficiency of cleaning low-concentration gas flows, focusing of elastic vibrations is carried out using a lens made in the form of a conical plane-curved body formed by sectioning a cone with two planes parallel to its height and to the base installed inside a rotating wedge-shaped adapter that provides rotation of the lens.

When implementing the process of coagulation of particles according to [3], the emitter of acoustic vibrations acts on foreign particles, which leads to their mutual oscillation, association and deposition.

At the same time, the increased intensity of focusing due to focusing and rotation of the zone of increased intensity (focusing zone) can partially eliminate the disadvantages of the known methods, but they do not provide a significant increase in the efficiency of coagulation of foreign particles in gas flows for the following reasons:

- significant energy losses of elastic vibrations during reflection, transmission and focusing of high-intensity vibrations using lenses from material media reduce the maximum radiation intensity in the coagulation zone;

- the low focusing efficiency of low-frequency ultrasonic vibrations generated by gas-jet emitters (the diameter of the focus line will exceed several wavelengths, which will be about 10 cm for a frequency of 10 kHz in air) does not allow creating a zone of increased radiation intensity (more than 170 dB);

- the limited speed of rotation of the lens, due to the limited capabilities of mechanical rotation systems, perpendicular to the axis of the pipeline does not allow for uniform impact over the cross section of the pipeline;

- the need for repair and maintenance of focusing devices (lenses) operating in dusty streams, in the presence of abrasive particles, reduces the time of continuous implementation of the method.

In addition, the method according to [3] has all the main disadvantages due to the use of gas-jet emitters, namely:

- low efficiency [5] used to implement the method of coagulation of gas-jet emitters of the Hartmann type (efficiency less than 20 ... 25%);

- a limited range of radiation frequencies (less than 20 kHz), excluding the possibility of effective coagulation of small particles, since it is known [6] that the coagulation efficiency largely depends on the degree of entrainment of dispersed particles by a dispersion medium, which is defined as:

,

,

where µ is the dynamic viscosity coefficient of the dispersion medium, ρ is the density of the dispersed phase / particles, R is the particle radius.

In this case, the ratio of the amplitude of the oscillation velocity of the suspended particle to the amplitude of the oscillation velocity of the dispersion medium, depending on the ratio of the sound emission frequency f to the characteristic frequency F _0, is asymptotic. For example, for air, under normal conditions

therefore, the optimal frequency of acoustic exposure is determined by the formula

.

.

Thus, for coagulation of particles with sizes of 15 ... 20 microns and less, it is necessary to carry out exposure to ultrasonic vibrations in the frequency range of 20 ... 30 kHz.

In the proposed technical solution, the task is to create a method for coagulation of foreign particles in gas streams, which would be free from the above disadvantages, the implementation of which would increase the efficiency of coagulation, and the achieved degree of purification would be practically independent of either the dispersion or the concentration of polluting particles in the cleaned environment, nor from their ability to coagulate.

The essence of the proposed technical solution is that in the method of coagulation of foreign particles in gas flows, which consists in exposing the particles to elastic vibrations focused in a line rotating perpendicular to the axis of the pipeline, the length of which corresponds to the transverse dimension of the pipeline, the elastic vibrations are created by a powered electronic oscillator, oscillating longitudinally and a piezoelectric transducer rotating along the acoustic axis emits and focuses elastic vibrations mechanically and acoustically coupled with a transducer, an emitter in the form of a rectangular, stepwise variable in thickness plate, bending vibrations relative to the larger of its axes at frequencies that are multiples of the main axis, in the range from 30 to 20 kHz, they simultaneously focus the vibrations generated by both sides of the rectangular plate, and the vibrations generated back to the particle flow by the side of the emitter, direct to it after reflection and passage of a distance exceeding the longitudinal size of the emitter by an amount multiple of half the length waves emitted by ultrasonic vibrations in the air.

Thus, in the proposed method for the coagulation of foreign particles in a gaseous medium, the task of increasing the efficiency of the process is solved by:

- the creation of ultrasonic vibrations by a powered electronic generator, longitudinally oscillating and rotating along the acoustic axis of the piezoelectric transducer, acoustically associated with a bending oscillator emitter;

- radiation and focusing of elastic vibrations mechanically and acoustically associated with the emitter in the form of a rectangular, stepwise variable in thickness of the plate, making bending vibrations relative to the largest of its axes at multiples of the main frequency in the range from 30 to 20 kHz;

- simultaneous focusing of the vibrations generated by both sides of the rectangular plate, and the vibrations created by the emitter side opposite to the particle flow, direct to it after reflection and passage of a distance exceeding the longitudinal size of the emitter by a multiple of half the wavelength of the emitted ultrasonic vibrations in air.

The essence of the proposed technical solution is illustrated in figure 1.

The proposed method is implemented using emitting and focusing elastic vibrations of the emitter 1, made in the form of a rectangular, stepwise variable in thickness of the plate, rotating together with the piezoelectric transducer 2. The electric power of the transducer 2 is provided by an electronic generator (not shown in Fig. 1). The emitter is installed in a special reflector 3. The emitter performs bending vibrations relative to the larger of its axes at frequencies in the range from 30 to 20 kHz, which are multiples of the main one, and due to the emission of vibrations with certain phases from sections of different thicknesses (the phase of the emitted oscillations is determined by the thickness of the section) focusing vibrations. Due to the fact that the vibrations of the opposite side of the emitter are also generated from sections with different thicknesses with different phases, the vibrations generated by both sides of the rectangular plate are simultaneously focused, and the vibrations created by the emitter side opposite to the particle flow are directed to the focusing zone after reflection and propagation distances exceeding the longitudinal size of the emitter by an amount multiple of half the wavelength of the emitted ultrasonic vibrations in the air.

The proposed method of ultrasonic coagulation is implemented as follows. The electric motor 4 and the ultrasonic generator are turned on (not shown in FIG. 1). In this case, the emitter 1 together with the piezoelectric transducer 2, using a belt drive, starts to rotate around its own axis with an angular velocity proportional to the velocity of the input stream of the pipeline 6. The acoustic vibrations emitted by the plate are formed in focus, which is a line rotating perpendicular to the axis of the pipeline, the length of which corresponds to the transverse size of the pipeline, and affect the solid particles of the gas stream. Under the action of ultrasonic vibrations, solid particles coagulate into larger ones and settle into the hopper 5. The cleaned gas stream exits through the pipeline 7. The impact on suspended foreign particles during coagulation is carried out simultaneously by vibrations created by both sides of the flat emitter, and the vibrations generated back to the particle flow side of the emitter, direct to it after reflection and passage of a distance exceeding the longitudinal dimension of the emitter by an amount multiple of half the length Waves of ultrasonic vibrations in air.

Thus, the uniformity of the acoustic (ultrasonic) effect along the entire diameter of the pipeline with the emitting surface, which exceeds the area of the emitter directly by at least twice, is ensured.

Developed to implement the proposed method, the device has the following technical characteristics: for the formation and focusing of acoustic vibrations in a pipeline with a diameter of 500 mm, a radiator in the form of a bending-oscillating plate 250 × 70 mm in size is used. By oscillating at modes 3 and 5 in the frequency range from 20 to 30 kHz, the emitter provides at near-focal length (up to 0.5 m), the formation of ultrasonic vibrations with a sound pressure level of 130 ... 170 dB, at the focal length (0.5 m) - 180 dB As the distance from the focus of the emitter increases, the sound pressure level decreases. The sound pressure level distribution is schematically shown in FIG. 1 in the form of shaded areas with the indicated sound pressure levels. The material of the emitter and concentrator is a titanium alloy; reflector size 500 × 140 mm; reflector material - metal.

To determine the effectiveness of the proposed method of coagulation and establish the functionality of the created equipment, experimental studies were carried out by improving the cleaning system by introducing ultrasonic vibrations into the design of the source. Based on experimental studies, it was found that the introduction of the ultrasonic vibrations source into the design of the exhaust gas purification system of one of the boiler houses in the city provides an increase in the efficiency of the existing purification system to 99.5% (from 82%) due to the possibility of trapping micron-sized particles.

Thus, the proposed method provides an increase in the efficiency of ultrasonic coagulation.

The method for coagulation of foreign particles in a gaseous medium developed in the laboratory of acoustic processes and apparatuses of the Biysk Technological Institute of Altai State Technical University passed laboratory and technical tests and was practically implemented in an existing installation. Small-scale production of devices is scheduled to begin in 2011.

Bibliography

1. Khmelev V.N .. Ultrasonic coagulation chamber for operation in aggressive environments [Text] / V.N. Khmelev, A.V. Shalunov, K.V. Shalunova // Modern problems of radio electronics: collection of books. scientific tr / scientific Ed .: A.I. Gromyko, A.V. Sarafonov; open for issue: A.A. Levitsky. - Krasnoyarsk: IPK SFU, 2009 .-- 465 p.

2. Copyright certificate No. 1029996.

3. Copyright certificate No. 927280 - prototype.

4. Ultrasonic gas-jet emitter [Text]: US Pat. 1789301 Ros. Federation: IPC 5 B06B 1/20 / Mitin A.G., Khmelev V.N. (Russia), applicant: Scientific-Production Association "ALTAY", application, 4898490 from 01/02/1991. Published on January 23, 1993.

5. Sources of powerful ultrasound [Text] / ed. L.D. Rosenberg. - M .: Nauka, 1967 .-- 265 p.

6. Yudaev B.F. Acoustic coagulation of aerosols. Bulletin of construction equipment, 2004, No. 6.

Claims (1)

A method of coagulation of foreign particles in gas flows, which consists in exposing the particles to elastic vibrations, focused into a line rotating perpendicular to the axis of the pipeline, the length of which corresponds to the transverse dimension of the pipeline, characterized in that the elastic vibrations create a piezoelectric transducer longitudinally oscillating and rotating along the acoustic axis, powered by an electronic generator, emit and focus elastic vibrations mechanically and acoustically associated with the transducer emitter in the form of a rectangular, stepwise variable over the thickness of the plate, performing bending vibrations relative to the larger of its axes at frequencies that are multiples of the main axis, in the range from 30 to 20 kHz, the vibrations generated by both sides of the rectangular plate are simultaneously focused, and the vibrations generated back to the flow particles side of the emitter, direct to it after reflection and the passage of a distance exceeding the longitudinal size of the emitter by an amount multiple of half the wavelength of the emitted ultrasonic vibrations in out of breath.

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