Impedance perforated plate resonance type waste heat boiler chimney silencer and design method thereof

Abstract

The application provides an effective and cost-saving design method for an impedance perforated plate resonance type waste heat boiler main chimney silencer, which comprises the following steps: S1, determining the mounting form of the silencing sheet according to the diameter of the channel; S2, determining the thickness and spacing of the silencing sheet; S3, determining the relevant parameters of the outer perforated plate; S4, determining the size of each air cavity and the relevant parameters of the inner perforated plate according to the impedance perforated plate resonance silencing structure; the application does not need to fill sound-absorbing materials, and avoids the situation that the silencer is disabled due to dust blockage; and the impedance silencing structure is more sensitive to medium and low frequency noises, and reasonable control of the relevant parameters such as the hole diameter and the number of the perforated plate can control the noise reduction frequency within a certain frequency range, thereby obtaining a good silencing effect.

Description

Technical Field

[0001] This invention belongs to the field of noise reduction of main chimneys for industrial waste heat boilers, specifically involving an impedance perforated plate resonant waste heat boiler chimney silencer and its design method. Background Technology

[0002] Currently, with the accelerated deployment of gas turbine power plants, noise pollution from these plants has become a major environmental concern. The main chimney of the waste heat boiler, as the final stage equipment in a gas turbine power plant, serves as both a waste discharge channel and, due to its high location and large noise pollution radiation area, is a primary target for noise reduction control in gas turbine power plants. To reduce the adverse environmental impact of noise from the waste heat boiler's main chimney outlet, resistive silencers are commonly used. However, the effectiveness of resistive silencers is not ideal. The reasons are as follows: First, resistive silencers primarily utilize the sound absorption properties of porous sound-absorbing materials for noise reduction. This method is highly sensitive to high-frequency noise and has extremely limited effectiveness against mid- and low-frequency noise. Increasing the thickness and density of the sound-absorbing material can shift the sound absorption performance of the resistive silencer towards the mid- and low-frequency bands, but when the thickness and density of the sound-absorbing material reach a certain limit, the improvement in noise reduction effect is not significant, and the cost is high. Second, during the operation of the waste heat boiler, the flue gas contains a large amount of dust. After the equipment has been running for a period of time, the dust will clog the gaps in the sound-absorbing materials, leading to a decrease in the sound absorption performance of the materials or even their failure. In addition, ambient temperature and humidity also affect the performance of porous sound-absorbing materials. Third, when the flue gas enters the waste heat boiler cavity, the low-frequency noise caused by the eddy currents generated by the spiral finned tube array obstructing the flue gas is the main source of noise at the main chimney outlet. In addition, some mid- and high-frequency noise from the gas turbine flue gas will also be transmitted into the main chimney through the waste heat boiler body. In summary, using only resistive porous sound-absorbing material silencing structures cannot effectively solve the noise problem at the main chimney outlet of the waste heat boiler. Summary of the Invention

[0003] The purpose of this invention is to provide an effective and cost-saving design method for the silencer of the main chimney of an impedance perforated plate resonant waste heat boiler.

[0004] The design method for a silencer for a perforated plate resonant waste heat boiler chimney includes the following steps:

[0005] S1. The installation method of the silencer is determined based on the diameter of the channel. The calculation formula for the resistive silencer structure is as follows:

[0006] (1)

[0007] in, This refers to the noise reduction amount; The noise reduction coefficient; The effective length of the muffler; The perimeter of the channel section of the muffler; The effective cross-sectional area of ​​the muffler channel;

[0008] S2, determine the thickness and spacing of the sound-absorbing strips;

[0009] S3, Determine the relevant parameters of the external perforated plate;

[0010] S4, determine the size of each air cavity and the relevant parameters of the inner perforated plate based on the resistant perforated plate resonance silencing structure;

[0011] The perforated plate resonant sound-absorbing structure is actually a resonant sound-absorbing structure composed of multiple Helmholtz resonators connected in parallel. When the holes are evenly distributed and have the same diameter, its resonant frequency can be calculated by the following formula:

[0012] (2)

[0013] In the formula:

[0014] Speed ​​of sound; Perforation rate; The cavity thickness is in meters (m). The effective length of the neck is in meters (m).

[0015] The peak noise frequency can be obtained by measurement or simulation. The peak noise frequency from the waste heat boiler cavity is generally between 60-80 according to engineering measurements. The size of each air resonance chamber and the perforation diameter and perforation rate of the perforated plate on the resonance chamber are obtained according to formula (2).

[0016] Furthermore, when the diameter of the channel in S1 is less than 400mm, a single-channel cylindrical structure design is adopted; when the diameter is greater than 400mm, a multi-channel plate structure is adopted.

[0017] Furthermore, in step S4, when the natural frequency of the small chamber formed by the inner perforated plate and the air resonant cavity is consistent with the noise frequency, the movement speed of the air column within the air cavity is maximized, and the noise reduction effect is also optimized. In engineering, the perforated plate commonly used has a thickness of 1-10mm, a hole diameter of 2-15mm, a perforation rate of 0.5%-15%, and an air layer thickness of 50-250mm.

[0018] The beneficial effects of this invention are as follows: This invention does not require filling with sound-absorbing material, thus avoiding the failure of the silencer due to dust blockage; furthermore, the resistant silencing structure is more sensitive to medium and low frequency noise, and reasonable control of relevant parameters such as the diameter and number of perforated plates can control the noise reduction frequency within a certain frequency range, thereby obtaining a good silencing effect. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the impedance perforated plate resonant waste heat boiler chimney silencer structure of the present invention.

[0020] Figure 2 This is a cross-sectional view of the impedance perforated plate resonant sound-absorbing sheet structure of the present invention;

[0021] Figure 3 The diagram shows the appearance and partial cross-section of the impedance perforated plate resonant silencing sheet based on the present invention.

[0022] In the diagram: 1. Sound-absorbing plate support device; 2. Outer shell; 3. Perforated plate of the outer shell resonant cavity; 4. Sound-absorbing material of the shell; 5. Perforated protective panel of the sound-absorbing material of the shell; 6. Impedance perforated plate resonant sound-absorbing plate; 7. Frame; 8. Common back plate of the sound-absorbing plate resonant cavity; 9. Connector of the perforated plate inside the resonant cavity; 10. Perforated plate A inside the resonant cavity; 11. Sound-absorbing material; 12. Resonant cavity partition support; 13. External perforated protective panel; 14. Perforated plate B inside the resonant cavity; 15. Semi-circular perforated plate; 16. Back plate supporting the semi-circular perforated plate sound absorber. Detailed Implementation

[0023] The present invention will now be further described with reference to the accompanying drawings.

[0024] I. Determine the overall structural layout of the muffler based on the resistive silencing structure design method.

[0025] Depend on Figure 1 As shown, both the air resonance cavity in the muffler cylinder and the air resonance cavity in the silencing plate are equivalent to increasing the thickness of the porous sound-absorbing material. The entire muffler can be designed according to a resistive silencing structure. The resistive silencing structure determines whether to use a single-channel cylindrical or multi-channel plate structure based on the diameter of the channel. For diameters less than 400mm, a single-channel cylindrical structure can be used; for diameters greater than 400mm, a multi-channel plate structure is used, which increases the silencing area and, due to its low pressure loss, does not affect the chimney's exhaust function due to the addition of silencing equipment; moreover, the plate structure design is simple and easy to install (see...). Figure 1 Typically, the diameter of the main chimney of a waste heat boiler is greater than 2 meters, and it often adopts a design similar to... Figure 1 The multi-channel plate structure shown is a multi-channel plate structure. The multi-channel plate structure includes a sound-absorbing plate fixing device 1, an outer shell 2, an outer shell resonant cavity perforated plate 3, a shell sound-absorbing material 4, a shell sound-absorbing material perforated protective panel 5, and an impedance perforated plate resonant sound-absorbing plate 6. The impedance perforated plate resonant sound-absorbing plate 6 is fixed to the outer shell 2 by the sound-absorbing plate fixing device 1. The inner ring of the outer shell 2 is sequentially provided with the outer shell resonant cavity perforated plate 3, the shell sound-absorbing material 4, and the shell sound-absorbing material perforated protective panel 5. A shell sound-absorbing resonant cavity is formed between the outer shell 2 and the outer shell resonant cavity perforated plate 3.

[0026] The calculation formula for resistive noise reduction structure is as follows:

[0027] (1)

[0028] In the formula: The noise reduction is expressed in dB. The noise reduction coefficient; The effective length of the muffler is in meters (m). Let m be the perimeter of the channel section of the muffler; The effective cross-sectional area of ​​the muffler channel is m. 2 .

[0029] ① Determine the thickness and spacing of the sound-absorbing strips.

[0030] As shown in Formula 1, by rationally arranging the spacing and thickness of the sound-absorbing plates, the perimeter of the channel cross-section of the structure can be increased. and the effective cross-sectional area of ​​the channel Optimal for achieving the best noise reduction effect. The spacing between resistive noise reduction plates is typically 100-250mm, and the plate thickness is typically 50-250mm.

[0031] Impedance perforated resonant silencers have both sound-absorbing and air layers. To increase the silencing area, a symmetrical design with a shared back panel is used. The silencer thickness is typically 200-450mm. Once the silencer thickness is determined, the arrangement of the silencer can be completed by appropriately matching the number and spacing of the silencers.

[0032] ② Determine the relevant parameters of the external perforated plate

[0033] The primary function of the external perforated panel is as a protective panel for the porous sound-absorbing material. It needs to possess sufficient strength, and its thickness is typically 2-6mm. Furthermore, the external perforated panel, together with the rear resistive perforated panel, forms a double-layer perforated panel arrangement, further enhancing the sound absorption range of the rear resistive structure. The external perforated panel is designed with evenly distributed 6-15mm aperture holes, which satisfies the protective function of the front resistive panel and also helps improve the sound absorption range of the rear resistive panel.

[0034] II. Determine the size of each air cavity and relevant parameters of the inner perforated plate based on the resonant silencing structure of the resistant perforated plate.

[0035] The perforated plate resonant sound-absorbing structure is actually a resonant sound-absorbing structure composed of multiple Helmholtz resonators connected in parallel. When the holes are evenly distributed and have the same diameter, its resonant frequency can be calculated by the following formula:

[0036] (2)

[0037] In the formula:

[0038] The speed of sound is in m / s; Perforation rate; Let the cavity thickness be m; The effective length of the neck is in meters (m).

[0039] When the natural frequency of the chamber formed by the perforated plate and the air resonant cavity matches the noise frequency, the air column's velocity within the air cavity is maximized, resulting in optimal noise reduction. In engineering, perforated plates typically have a thickness of 1-10mm, a hole diameter of 2-15mm, a perforation rate of 0.5%-15%, and an air layer thickness of 50-250mm. Smaller hole diameters result in higher internal damping. To ensure the silencer's lifespan and balance manufacturing costs, perforated plates in engineering often use 2-4mm thick stainless steel plates with hole diameters of 6-10mm.

[0040] The peak noise frequency can be obtained through measurement or simulation. Engineering measurements show that the peak noise frequency from the waste heat boiler cavity is generally between 60 and 80. Based on this, the size of each air resonance chamber and the perforation diameter and perforation rate of the perforated plate on the resonance chamber can be obtained according to Formula 2.

[0041] Based on the above steps, the overall structural form of the impedance perforated plate resonant chimney silencer can be obtained.

[0042] like Figures 2-3 As shown, the impedance perforated plate resonant silencing sheet 6 includes a frame 7, a common back plate 8 for the silencing sheet resonant cavity, a perforated plate inside the resonant cavity, sound-absorbing material 11, and an outer perforated protective panel 13. The common back plate 8 for the silencing sheet resonant cavity is installed at the center of the frame 1. The perforated plate inside the resonant cavity is installed on the outside of the common back plate 8. The perforated plate inside the resonant cavity and the common back plate 8 for the silencing sheet resonant cavity form a resonant cavity. The impedance perforated plate resonant silencing sheet 6 is designed with a symmetrical structure of the common back plate. The back plate is not only an important part of the resonant cavity structure, but also provides a place for noise to be refracted and reflected in the resonant cavity, thus extending the noise attenuation path. The symmetrical design increases the silencing area and improves the overall noise reduction capability of the structure. The frame and the perforated plate inside the resonant cavity are connected by the perforated plate connector 9. Sound-absorbing material 11 and an outer perforated protective panel 13 are provided on the outside of the perforated plate inside the resonant cavity. The back plate 8 shared by the sound-absorbing sheet and the resonant cavity is connected to the outer perforated protective panel 13 by the resonant cavity partition support 12. The sound-absorbing material 11 is not only an important component of the resistive section, but also dampens and dissipates noise entering and exiting the resonant cavity of the reactive section, accelerating noise attenuation. The bottom of the frame 7 is connected to a semi-circular sound-absorbing perforated plate. A semi-circular sound-absorbing support back plate 16 is provided on the semi-circular sound-absorbing perforated plate 15. The semi-circular design not only guides the incoming noise flow, but the perforated plate + air cavity structure design also plays a role in silencing and reducing noise in some sound waves. This further enhances the overall structure's noise reduction capability.

[0043] An outer perforated plate, sound-absorbing material, and an inner perforated plate form a front-end resistive silencing structure. When sound waves enter and exit the sound-absorbing material, the sound energy is converted into heat energy and dissipated due to the frictional resistance of the material, thus achieving silencing and noise reduction. The characteristics of the sound-absorbing material 11 determine that the resistive silencing structure is more sensitive to mid- and high-frequency noise, and can reduce mid- and high-frequency noise transmitted from the furnace cavity to this location. A certain gap is left between the perforated plate and the back plate 8 shared by the silencing plate in the resonant cavity, forming an air cavity. The air cavity and the perforated plate in the resonant cavity form a rear-end resistive perforated plate resonant sound-absorbing structure. This resistive silencing structure utilizes the repeated vibration of air columns in the perforated plate's neck in the resonant cavity, similar to an air spring, to dissipate sound energy and achieve silencing. By reasonably controlling the volume of the air cavity, the thickness of the perforated plate in the resonant cavity, the aperture parameters, and the number of holes, the natural frequency of the air cavity can be made the same as the frequency of the sound wave to produce resonance, maximizing the movement speed of the air columns entering and exiting the holes, thereby achieving the best noise reduction effect. The air resonant cavity is equivalent to increasing the thickness of the porous sound-absorbing material. Therefore, the outer perforated plate + sound-absorbing material + inner perforated plate + resonant cavity can be considered as a resistive noise reduction structure. Thickening the sound-absorbing material shifts the structure's sound absorption frequency range to the mid and low frequencies, improving the noise reduction performance of the resistive noise reduction structure for mid and low frequency noise, and reducing structural design costs. In addition, the air resonant cavity design avoids the situation where dust blockage leads to muffler failure due to the use of sound-absorbing material alone, thus extending the muffler's service life.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An impedance perforated plate resonant waste heat boiler chimney silencer, comprising a multi-channel plate structure, the multi-channel plate structure comprising a silencer plate fixing device (1), an outer shell (2), an outer shell resonant cavity perforated plate (3), a shell sound-absorbing material (4), a shell sound-absorbing material perforated protective panel (5), and an impedance perforated plate resonant silencer (6); the impedance perforated plate resonant silencer (6) is fixed to the outer shell (2) by the silencer plate fixing device (1), the inner ring of the outer shell (2) is sequentially provided with the outer shell resonant cavity perforated plate (3), the shell sound-absorbing material (4), and the shell sound-absorbing material perforated protective panel (5), and a shell silencer resonant cavity is formed between the outer shell (2) and the outer shell resonant cavity perforated plate (3); the impedance perforated plate resonant silencer (6) comprises a frame (7), a silencer plate resonant cavity shared back plate (8), a resonant cavity inner perforated plate, sound-absorbing material (11), and an outer... The frame (7) has a perforated protective panel (13) and a semi-circular perforated sound-absorbing panel (15). A common back plate (8) for the sound-absorbing sheet resonant cavity is installed in the center of the frame (7). A perforated plate inside the resonant cavity is installed on the outside of the common back plate (8) for the sound-absorbing sheet resonant cavity. The perforated plate inside the resonant cavity and the common back plate (8) for the sound-absorbing sheet resonant cavity form a resonant cavity. The impedance perforated plate resonant sound-absorbing sheet (6) is designed as a symmetrical structure of the common back plate. The frame and the perforated plate inside the resonant cavity are connected by a perforated plate connector (9) inside the resonant cavity. A sound-absorbing material (11) and an outer perforated protective panel (13) are provided on the outside of the perforated plate inside the resonant cavity. The common back plate (8) for the sound-absorbing sheet resonant cavity and the outer perforated protective panel (13) are connected by a resonant cavity partition support (12). The bottom of the frame (7) is connected to the semi-circular perforated sound-absorbing panel. A semi-circular perforated sound-absorbing panel support back plate (16) is provided on the semi-circular perforated sound-absorbing panel (15).

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