CN114776390A - Final-stage stationary blade dehumidification structure based on ultrasonic waves - Google Patents

Abstract

The invention discloses an ultrasonic-based final-stage static vane dehumidification structure, comprising a hollow static vane, an ultrasonic sounding device, a trailing edge channel and a vibrating rod structure. The ultrasonic sounding device includes a piezoelectric ultrasonic transducer, a support device, and a fixed flange. and horn. Combined with the geometric characteristics of the blade outlet and the propagation performance of ultrasonic waves, the composite horn system formed by the horn and the vibrating rod can concentrate high-energy ultrasonic waves at the trailing edge position. Under the action of high-energy ultrasonic waves, the liquid film on the trailing edge of the blade is rapidly broken and atomized. Under the ultra-high atomization rate, the water erosion damage of secondary water droplets can be radically cured. At the same time, under different working conditions, it can adapt to different operating conditions by adjusting the input power, and its dehumidification efficiency is always maintained at a high level. The invention combines the ultrasonic water droplet elimination technology with the last stage blade, which greatly improves the dehumidification effect of the last stage blade of the saturated steam turbine, and has guiding significance for the improvement of the blade dehumidification technology and the combined application of the traditional dehumidification structure and other technologies.

Description

An Ultrasonic-Based Final Stage Static Leaf Dehumidification Structure

technical field

The invention belongs to the technical field of steam turbine machinery, and relates to a final-stage static blade dehumidification structure based on ultrasonic waves.

Background technique

The last stage blades of the saturated steam turbine basically work in the wet steam region. Wet steam will cause water erosion damage to the last few stages of moving blades, which not only reduces the working efficiency of steam turbine operation, but even threatens the safety of unit operation. With the rapid increase of the maximum power of a single steam turbine and the development of nuclear power steam turbines, the water erosion problem of the low-pressure last stages of the steam turbine blades is becoming more and more serious. Wet steam is composed of primary water droplets and a small amount of secondary water droplets, of which the secondary water droplets are larger in size, generally tens of times larger than the primary water droplets, and have poor follow-up with the main steam flow, and will generate dynamic unbalanced forces. , is considered to be the main cause of leaf water erosion. The droplets are deposited on the blade to form a water film, and with the continuous fusion of the water droplets, the thickness of the water film continues to increase. It will be gradually alluvialized to the tail end of the blade with the action of the airflow, and then separated from the blade to form a greater harm to the equipment. of secondary water droplets.

In order to reduce or prevent water erosion, the main technical means at present are to set dehumidification grooves on stationary blades by suction method, set moisture collection chambers on clapboards, set diversion grooves on moving blades and anti-corrosion processes.

There are three methods of static leaf dehumidification technology: static leaf suction method, static leaf heating method, and static leaf blowing method. The static vane suction method is the earliest method for dehumidification of hollow guide vanes. Based on this principle, the technology has the following problems: due to the pressure difference between the pressure surface and the suction surface, the water film flow will be generated, and the dehumidification efficiency is low; The surface tension is large, the pressure difference is difficult to suck small droplets, and the dehumidification effect is not ideal; for different structures and operating conditions, such as slot size, suction pressure flow, slot position, etc., the dehumidification effect is also different. For large units with peaks, the dehumidification effect is not ideal under variable working conditions. The stationary blade heating method, the structure is to introduce heat into the stationary blade cavity, heat the inner wall, and evaporate the water film layer on the outer surface, so that the trailing edge cannot form secondary large water droplets. In practical applications, it is necessary to consider how much heat is introduced. This method requires changing the structure of the equipment, which may lead to insufficient dehumidification due to insufficient heat. In the static vane purging method, a purging slot is machined on the trailing edge of the vane, and the higher-pressure steam is introduced into the guide vane, and then ejected from the trailing edge purging slot. This method reduces the size of the large water droplets falling off the trailing edge, accelerates the speed, and reduces the erosion to the moving blades. This method requires that the amount of purge steam and the direction angle need to be reasonably matched so as not to affect the main steam flow. When the load changes, the purge angle is difficult to change, resulting in increased aerodynamic losses. At the same time, this method breaks the secondary water droplets on the suction side, and the droplet deposition on the suction side is more obvious.

Combined with the above traditional dehumidification methods, the effect of preventing water erosion on leaves is limited. Compared with the conventional air cooling technology, the ultrasonic power is high and the energy is large. Ultrasonic waves have strong penetrating ability and generate cavitation shock waves when propagating in the medium. These inherent characteristics enable ultrasonic waves to transmit strong energy when propagating in the medium, resulting in strong impact and high efficiency. Using the mechanical stirring effect of ultrasonic waves, it can act on the trailing edge of the blade, so that the liquid film on the trailing edge can be quickly broken and atomized, which greatly reduces the harm of secondary water droplets.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the disadvantages of the traditional blade dehumidification effect, and to provide a final stage static blade dehumidification structure based on ultrasonic waves by utilizing the structural characteristics of the blade and the cavitation effect of ultrasonic waves. The invention utilizes the geometrical structure feature of the blade outlet, and constitutes a new composite horn system through the piezoelectric ultrasonic transducer, the horn and the vibrating rod structure. The vibrating rod is mechanically vibrated under the excitation of ultrasonic waves, and the liquid film on the blade surface is atomized due to cavitation, forming a uniform spray of small-sized droplets, which greatly reduces the hazard of secondary water droplets and effectively prevents the occurrence of water erosion. .

To achieve the above object, the present invention adopts the following technical solutions to realize:

An ultrasonic-based final-stage static vane dehumidification structure, comprising:

an ultrasonic sounding device, the ultrasonic sounding device is arranged in the inner cavity of the hollow stationary blade of the steam turbine;

The vibrating rod structure is arranged at the exit of the trailing edge of the hollow stationary blade of the steam turbine, and is connected with the ultrasonic sounding device.

The further improvement of the present invention is:

The ultrasonic sounding device is provided with several groups, all of which are distributed along the blade height of the hollow stationary blade of the steam turbine.

The ultrasonic sounding device includes a piezoelectric ultrasonic transducer and a horn, and the piezoelectric ultrasonic transducer is connected to one end of the horn through a fixed flange; The inside of the blade; a section of the horn is connected to the vibrating rod structure.

A through hole is opened at the trailing edge of the hollow stationary blade of the steam turbine, and the horn is passed through the through hole and connected to the vibrating rod structure.

The horn is a rod-shaped structure obtained by adopting the theoretical design of the exponential horn.

The diameter of the horn gradually decreases from the side connected with the fixed flange to the side connected with the vibrating rod structure, and the contact section of the end with the smaller diameter and the vibrating rod structure is welded by rounding.

The piezoelectric ultrasonic transducer is connected to an external power source through an amplifier, and the piezoelectric ultrasonic transducer adopts an ultrasonic transducer capable of generating ultrasonic waves of 40-60 kHz.

The outer surface of the vibrating rod structure is a structure obtained after rough processing.

The shape of the outer surface of the vibrating rod structure is consistent with the profile line at the exit of the trailing edge of the hollow stationary blade of the steam turbine.

Compared with the prior art, the present invention has the following beneficial effects:

The invention adopts an ultrasonic-based final-stage stationary blade dehumidification structure, which can be combined with the existing final-stage blades with collection or suction slits and other structures, thereby significantly improving the dehumidification effect of the final-stage blades. Compared with the conventional dehumidification structure, the trailing edge of the last stage blade is the place where the secondary water droplets are generated, and the space of the trailing edge is limited, so the traditional dehumidification structure cannot be arranged on the trailing edge. The invention introduces technologies such as ultrasonic waves, and directly eliminates the secondary water droplets in the production process. The micro ultrasonic device consumes less power, has a short atomization time, and the atomization rate can be as high as 95%. The atomized droplets have small particle size and distribution. At the same time, this part of the working fluid can enter the mainstream to do work again. Under different working conditions, due to the pressure difference and the deviation of the main deposition position of the liquid film, the dehumidification effect of the suction slit will change, and the present invention can adapt to different working conditions by changing the input power, and the dehumidification efficiency is always maintained at a high level . At the same time, the secondary water droplet crushing effect on the suction surface and the pressure surface of the blade is obvious, which avoids the phenomenon of droplet deposition on the suction surface of the static blade purging method.

In order to describe the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings that need to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore do not It should be regarded as a limitation of the scope, and for those of ordinary skill in the art, other related drawings can also be obtained according to these drawings without any creative effort.

Description of drawings

In order to describe the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings that need to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore do not It should be regarded as a limitation of the scope, and for those of ordinary skill in the art, other related drawings can also be obtained according to these drawings without any creative effort.

Fig. 1 is the schematic diagram of the ultrasonic dehumidification structure of the final stage stationary blade of the present invention;

2 is a schematic structural diagram of a single ultrasonic sounding device and a vibrating rod of the present invention;

Among them, 1-steam turbine hollow stationary blade; 2-ultrasonic sounding device; 3-trailing edge channel; 4-vibrating rod structure; 5-piezoelectric ultrasonic transducer; 6-supporting device; 7-fixed flange; 8-transformer horn.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. The components of the embodiments of the invention generally described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

Thus, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that like numerals and letters refer to like items in the following figures, so once an item is defined in one figure, it does not require further definition and explanation in subsequent figures.

In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inside", etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings , or the orientation or positional relationship that the product of the invention is usually placed in use, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed in a specific orientation and operation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are only used to differentiate the description and should not be construed to indicate or imply relative importance.

Furthermore, the presence of the term "horizontal" does not imply that the component is required to be absolutely horizontal, but rather may be tilted slightly. For example, "horizontal" only means that its direction is more horizontal than "vertical", it does not mean that the structure must be completely horizontal, but can be slightly inclined.

In the description of the embodiments of the present invention, it should also be noted that, unless otherwise expressly specified and limited, the terms "set", "installed", "connected" and "connected" should be understood in a broad sense. It can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be internal communication between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

Below in conjunction with accompanying drawing, the present invention is described in further detail:

Referring to FIG. 1, an embodiment of the present invention discloses a final stage static vane dehumidification structure based on ultrasonic waves, including a steam turbine hollow static vane 1, an ultrasonic sounding device 2, a trailing edge channel 3 and a vibrating rod structure 4; as shown in FIG. 2, The ultrasonic sounding device 2 includes a piezoelectric ultrasonic transducer 5 , a supporting device 6 , a fixing flange 7 and a horn 8 .

The ultrasonic sounding device 2 is distributed along the blade height and is arranged in the inner cavity of the hollow stationary blade 1 of the steam turbine. The shape of the outer surface of the vibrating rod structure 4 is consistent with the profile at the exit of the trailing edge. The piezoelectric ultrasonic transducer 5 and the horn 8 are connected together by a fixed flange 7 to reduce assembly errors. At the same time, the support device 6 is connected to the fixed flange 7 and the inner wall of the hollow stationary blade 1 of the steam turbine, so as to play the role of fixed support and no leakage wave will occur. A hole is opened at the trailing edge of the hollow stationary blade 1 of the steam turbine, and the horn 8 is connected to the vibrating rod structure 4 through the trailing edge channel 3, and the vibrating rod structure 4 is fixed on the blade through a small contact surface. The outer surface of the vibrating rod structure 4 is roughened. The horn 8 is designed by using the exponential horn theory, which has better energy gathering effect. The horn 8 and the vibrating rod structure 4 are combined into a complex horn device. The small diameter end of the horn 8 and the contact section of the vibrating rod structure 4 are rounded welded to avoid stress concentration, and have good ultrasonic conduction capability and small acoustic resistance. In order to ensure the crushing effect, the piezoelectric ultrasonic transducer 5 can provide ultrasonic waves of 40-60 kHz. After the installation is completed, the harmonic response analysis is carried out on the complex vibration system composed of each ultrasonic sounding device 2 and the steam turbine hollow stationary blade 1, and the optimal debugging frequency is obtained. Under working conditions, the ultrasonic wave passes through the composite horn system composed of the horn 8 and the hollow stationary blade 1 of the steam turbine, and a large amount of energy is concentrated at the trailing edge. The liquid film at the trailing edge of the hollow stationary blade 1 of the steam turbine is rapidly broken and atomized under the action of sound waves, and does work with the main flow, reducing the hydrophobic loss and water erosion to the moving blades. At the same time, when the operating conditions of the steam turbine change, the input power of the external power supply is adjusted in time, so that the structure is always kept in a high-efficiency dehumidification state.

Principle of the present invention:

In a wet steam turbine, wet steam is composed of primary water droplets and a small amount of secondary water droplets, of which the secondary water droplets have a larger particle size, have poor follow-up with the mainstream steam, and generate dynamic unbalanced force, which is the cause of blade water erosion. main reason. The secondary water droplets of wet steam are mainly produced by the mainstream tearing the liquid film on the trailing edge of the blade. According to the experimental study on the measurement of the secondary water droplets in the wet steam of the 330MW low-pressure steam turbine, when the average particle size of the secondary water droplets is about 100μm, the average velocity is 50m/s; when the average particle size of the secondary water droplets is about 145μm, the average velocity is 20m/s . The smaller the average particle size of the secondary water droplets, the higher the average speed, the better the followability with the mainstream, the smaller the impact on the moving blades, and the smaller the water erosion hazard. The thickness of the liquid film on the trailing edge of the blade is small, far below the critical thickness of the liquid film entering the breaking oscillation. Under the action of ultrasonic oscillation, the surface with very small liquid film thickness can quickly enter the crushing atomizer under ultrasonic excitation, and atomize quickly. At the same time, according to the traditional sonic atomization particle size diameter prediction formula and related similar experimental data, it can be deduced that under a certain power of ultrasonic excitation, the secondary droplets generated by the trailing edge of the last stage blade will be rapidly atomized, and the atomization rate will increase. It can reach more than 95% and form a micro-jet with an average particle size of less than 10 μm, which greatly reduces the hazard of secondary water droplets.

The trailing edge of the blade is often a thin wedge-shaped geometry. In order to ensure that the vibration rod structure 4 does not affect the aerodynamic characteristics of the mainstream, it needs to be consistent with the profile of the trailing edge of the blade, and basically presents a wedge-like structure. The wedge-shaped structure has a concentrating effect on ultrasonic waves. Therefore, combined with the geometric characteristics of the blade outlet and the propagation performance of ultrasonic waves, the horn 8 and the vibrating rod structure 4 form a new type of composite horn 8 system, which can concentrate high-energy ultrasonic waves on the trailing edge of the blade. Under the action of high-energy ultrasonic waves, the liquid film on the trailing edge of the blade is rapidly broken and atomized. Under the ultra-high atomization rate, the water erosion damage of secondary water droplets can theoretically be cured.

Ultrasonic breaking of droplets mainly relies on the cavitation of ultrasonic waves. Ultrasonic cavitation refers to the dynamic process of growth and collapse of the micro-air nucleus cavitation bubbles existing in the liquid vibrating under the action of sound waves, and when the sound pressure reaches a certain value. A large number of small air bubbles can be generated when ultrasonic waves are applied to the liquid. One reason is that there is a local tensile stress in the liquid to form a negative pressure. The reduction of the pressure makes the gas originally dissolved in the liquid supersaturated, and escapes from the liquid as small bubbles. Another reason is that the strong tensile stress "rips" the liquid apart into a cavity called cavitation. The sound field factors that affect acoustic cavitation are frequency and sound intensity. As the ultrasonic frequency increases, the cavitation process becomes more difficult to occur. And as the frequency increases, the attenuation during the propagation of the sound wave increases. In order to obtain the same sonochemical effect, high-frequency ultrasound needs to pay more energy consumption. Therefore, the ultrasonic frequency used for sonochemical reaction is usually 20-50 kHz. The sound intensity is above the acoustic cavitation threshold sound intensity. Increasing the sound intensity will increase the output of the sonochemical reaction. However, when the sound intensity exceeds a certain limit, the cavitation bubbles may grow too large in the expansion phase of the sound wave, so that the The cavitation bubbles in the compressed phase have no time to collapse, thereby weakening the cavitation effect.

Under the action of ultrasonic oscillation, a single droplet will experience a dynamic deformation period and a broken atomization zone, and the dynamic deformation zone consumes more acoustic energy. The first stage is the dynamic deformation period of the droplet, the droplet leaves the equilibrium position due to the ultrasonic oscillation at the bottom, stretches, deforms, and spreads into a liquid film; the second stage is the breakup and atomization period of the droplet, when the droplet deforms, When the liquid film spreading and the ultrasonic energy inside the droplet reach a critical state, the surface of the droplet begins to peel off, break up, and finally atomize completely. The surface with a very small liquid film thickness can quickly enter the crushing atomizer under ultrasonic excitation and atomize quickly. According to the literature, under the action of ultrasonic vibration, the sample droplets are atomized after the pinch-off effect, and the atomized particle size distribution is mainly concentrated at about 1 μm.

Ultrasonic atomization has the advantages of small particle size of atomized droplets, uniform distribution and easy control, and is a good atomization technology. The combination of ultrasonic water droplet removal technology and the last stage blades greatly improves the dehumidification effect of the last stage blades of saturated steam turbines, which has guiding significance for the improvement of blade dehumidification technology and the combination of traditional dehumidification structures and other technologies.

The present invention is a final stage static vane dehumidification structure based on ultrasonic waves, which includes a steam turbine hollow static vane 1, an external power supply, an amplifier, a piezoelectric ultrasonic transducer 5, a fixed flange 7 and a support device 6, a horn 8, an external Vibration rod structure 4 with roughened surface. The arrangement of the ultrasonic sounding device 2 needs to be as consistent as possible with the trailing edge profile. When the steam turbine is running, the piezoelectric ultrasonic transducer 5 generates ultrasonic waves under the action of the external power source, the external power source generates high-frequency current through the amplifier, and the piezoelectric ultrasonic transducer 5 vibrates under the action of the high-frequency current to generate ultrasonic waves and ultrasonic waves. Through the amplification structure such as the horn 8, it is transmitted to the vibrating rod structure 4 at the trailing edge of the blade, and the cavitation effect of the ultrasonic wave at the trailing edge can break the liquid film on the trailing edge of the blade and reduce the generation of secondary droplets, thereby realizing the impact of the blade on the blade. dehumidification effect. The ultrasonic wave oscillates the liquid film at the trailing edge, breaking the liquid film at the trailing edge, greatly reducing the generation of secondary water droplets, thereby preventing water erosion. At the same time, according to the humidity distribution of the leaves under different working conditions, the appropriate input power is adjusted so that the leaves are always efficiently dehumidified. The ultrasonic sound generating devices 2 are not limited to four in the present invention, and may be smaller or larger than four.

The invention utilizes a large number of micro ultrasonic sound generators 2 arranged along the blade height direction, which are located inside one hollow stator blade of the steam turbine. It can adapt to the characteristics of the variable-section blades in the final stage of different steam turbines, and through the adjustment of the device, the dehumidification effect on the trailing edge of each section blade can be guaranteed to the greatest extent possible. The ultrasonic sounding device 2 is fixed in the inner cavity of the hollow stationary blade 1 of the steam turbine through the supporting device 6 . Based on the mechanism of ultrasonic cavitation, the present invention performs a certain rough treatment on the vibrating rod structure 4 to provide sufficient cavitation nuclei when ultrasonic waves act on the liquid film, and aggravate the cavitation of the liquid film.

The above are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. An ultrasonic-based last stage stationary blade dehumidification structure, comprising:

the ultrasonic sound-producing device (2), the ultrasonic sound-producing device (2) is arranged in the inner cavity of the hollow stationary blade (1) of the steam turbine;

the vibrating bar structure (4), the vibrating bar structure (4) sets up the trailing edge exit at hollow stator blade (1) of steam turbine to link to each other in ultrasonic sound generating mechanism (2).

2. The last stage stationary blade dehumidification based on ultrasonic waves of claim 1, characterized in that said ultrasonic sound emitting means (2) are provided in several groups, all distributed along the height of the hollow stationary blade (1) of the steam turbine.

3. The last stage stationary blade dehumidification based on ultrasonic wave of claim 1 or 2, characterized in that the ultrasonic sound generating device (2) comprises a piezoelectric ultrasonic transducer (5) and a horn (8), the piezoelectric ultrasonic transducer (5) is connected with one end of the horn (8) into a whole through a fixed flange (7); the fixed flange (7) is arranged inside the hollow stationary blade (1) of the steam turbine through the supporting device (6); one section of the amplitude transformer (8) is connected with the vibrating rod structure (4).

4. The last stage stationary blade dehumidification structure based on ultrasonic wave of claim 3, wherein the hollow stationary blade (1) of the steam turbine is provided with a through hole at its trailing edge, from which the horn (8) is extended to connect with the vibrating rod structure (4).

5. An ultrasonic-based last stage stationary blade dehumidifying structure as claimed in claim 3, wherein the horn (8) is a rod-like structure designed using an exponential horn theory.

6. The last stage ultrasonic-based stationary blade dehumidification structure according to claim 3, wherein the horn (8) has a diameter that gradually decreases from a side connected to the fixed flange (7) to a side connected to the vibratory rod structure (4), and a contact section of the small-diameter end with the vibratory rod structure (4) is welded by rounding.

7. The last-stage stationary blade dehumidification structure based on ultrasonic waves as set forth in claim 3, wherein the piezoelectric ultrasonic transducer (5) is connected to an external power source through an amplifier, and the piezoelectric ultrasonic transducer (5) is an ultrasonic transducer capable of generating ultrasonic waves of 40-60 kHz.

8. The last stage stationary blade dehumidification based on ultrasonic wave of claim 1, characterized in that the external surface of said vibrating rod structure (4) is a roughened structure.

9. The ultrasonic-based last stage stationary blade dehumidifying structure of claim 1, wherein the shape of the outer surface of the vibratory rod structure (4) conforms to the profile at the trailing edge outlet of the steam turbine hollow stationary blade (1).

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