JP3207896B2 - Silencer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a muffler installed in a duct through which gas flows to effectively reduce noise that increases at a specific frequency (for a blower, the fundamental frequency and harmonics).

[0002]

2. Description of the Related Art Conventionally, as a muffler installed in a duct through which gas flows, for example, a sound absorbing splitter or a sound absorbing cell provided with a sound absorbing surface parallel to the gas flow as shown in FIG. Those with a built-in structure are well known. However, in the sound-absorbing silencer having such a structure, the aperture ratio of the perforations provided in the cover 11 that covers the sound-absorbing material 9 cannot be made too large in order to prevent the sound-absorbing material 9 from scattering.

[0003] Therefore, the solid portion in the gas causes clogging of the opening, which tends to cause a reduction in the noise reduction performance. In particular,
In silencers installed in the flue of coal-fired boilers, etc., before and after the exhaust gas induction ventilator, the pores on the sound-absorbing surface due to the large amount of ash powder contained in the exhaust gas are remarkably clogged, and the performance of the silencer sharply increases. In some cases. Also, the silencer must be cleaned frequently to prevent this.

On the other hand, many noise sources, such as blowers, generate noise that peaks at a specific frequency (basic frequency and harmonic) in relation to the number of blades and the number of rotations. It is difficult to obtain an effective noise reduction effect by using a muffler having only a sound absorbing type structure even for noise having a specified peak frequency.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems in the prior art. According to the first aspect of the present invention, there is little deterioration in performance over time and efficient attenuation of noise whose peak frequency is specified. It is an object of the present invention to provide a muffler that has a large muffling effect even when there are a plurality of peak frequencies (overtones) at which noise increases, in addition to the above. The task is to

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a muffler which is installed in a duct through which gas flows and which effectively reduces noise that increases at a specific frequency. A plurality of silencing members arranged at right angles or inclined to the flow direction of the gas at intervals in the flow direction, and a closing member for closing one end of the plurality of muffling members. A silencing member, wherein the silencing member includes a sound absorbing material filled therein and a plurality of small holes provided on a downstream side surface in a gas flow direction, and is formed by the silencing member and the closing member. The depth of the space portion in the direction perpendicular to the flow direction is set to one of the wavelengths of the noise that increases at the specific frequency.
According to a second aspect of the present invention, in addition to the features of the first aspect, there are a plurality of the specific frequencies, and the muffling section is provided in the flow direction of the space portion. And a plurality of muffling portions each having a depth in a direction perpendicular to the wavelength range of 1/3 to 1/6 of each wavelength of the noise increasing at the plurality of frequencies.

[0007]

According to the first aspect of the present invention, a plurality of muffling members are arranged in the flow direction at a right angle or at an angle to the flow direction of the gas at intervals, and one end thereof is closed by a closing member. Since the muffler is provided, a space is formed in the muffler by the muffling member and the closing member, and the space forms a side branch in the duct. Since the depth in the direction perpendicular to the flow direction of the space portion is set to about 1/3 to 1/6 of the wavelength of the noise peaking at a specific frequency, the side branch portion functions as a resonance cavity, and the noise energy is reduced. The short-circuit causes a silencing effect at this portion. Furthermore,
Since the sound absorbing member is filled inside the sound absorbing member and a number of small holes are provided on the side opposite to the gas flow direction, a sound absorbing effect due to sound absorption of the sound absorbing material occurs in this portion. In this case, the small holes are opened on the downstream side with respect to the gas flow direction, and the ejector action due to the flow velocity of the main flow occurs in the space, so that solids in the gas are less likely to be deposited in the space and the small holes are formed. Is not blocked, and since the gas flow does not directly hit the small holes, the sound absorbing material is not scattered. Further, since there is no scattering of the sound absorbing material, it is possible to increase the aperture ratio of the small holes, thereby improving the sound absorbing effect and further preventing the small holes from being blocked.

According to the second aspect of the present invention, when there are a plurality of specific frequencies, the silencer is constituted by a plurality of silencers corresponding to the respective frequencies. Noise peaking at a plurality of frequencies can be effectively silenced.

[0009]

FIG. 1 shows a schematic configuration of a muffler according to an embodiment. Silencer is provided as part of the duct 1, as a plurality of muffling section, noise attenuation portion A ₀ of the fundamental frequency of the blower
It is constituted by the zone 2 and the second harmonic overtone sound-damping unit A ₁ zone 3. Each of the muffling units is a plurality of muffling splitters 4 or 5 that are a plurality of muffling members arranged in the flow direction at a slight inclination from the flow direction of the exhaust gas from the coal-fired boiler as a gas. And a casing 6 or 7 as a closing member disposed so as to close one end of the sound absorbing splitters 4 and 5. These are integrally connected and attached to the duct 1 via a flange 8. The space formed by the casing 6 or 7 and the sound absorbing splitter 4 or 5 has a depth (depth) of W ₀ or W ₁ and H ₀ or H ₁ , respectively, as shown in the figure.
Having an interval of

Furthermore, each of the sound absorbing splitters 4 or 5
Has a sound absorbing material 9 such as rock wool inside.
And a large number of small holes 10 are provided on the surface on the downstream side in the flow direction of the exhaust gas. Each of the sound absorbing splitters 4 and 5 has a solid plate on the upstream side and a material with a high aperture ratio such as expanded metal on the downstream side.

The exhaust gas system of a coal-fired boiler is often provided with an exhaust gas induction ventilator. Such a ventilator usually has a plurality of blades, and the rotation of the blades generates peak noise that is maximum or maximum at a fundamental frequency corresponding to the number of blades and a frequency that is an integral multiple of the fundamental frequency. Here the noise spectral fundamental frequency f ₀ (H _z), when the number of blades Z, the rotational speed of the impeller and N (rpm), an f ₀ = NZ / 60, the f ₀ and at least a muffler 2f it is necessary to efficiently attenuate the noise reaches a peak at a frequency of _0. Assuming that the wavelengths of the noise having such a frequency are λ ₀ and λ ₁ corresponding to the fundamental frequency and the second harmonic, respectively,
Assuming that the sound speed is c, λ ₀ = c / f ₀ and λ ₁ = c / 2f ₀ .

Meanwhile, the resonance frequency f _p of the side branch of the depth l _p is theoretically expressed as f _p = c / 4l _p. Therefore, in order to mute by short noise energy by resonance by the side branch portion, the depth l _p, it is sufficient to _{l p = c / 4f p =} λ / 4.

Therefore, in the present invention, the sound absorbing splitters 4, 5
In the range of substantially silencing effect is obtained by the resonance effect, respectively W ₀ or W ₁ shown in FIG. 1, which corresponds to _{l p, W 0 = λ 0} / 3~λ 0/6 W 1 = λ 1 / 3~λ is set to be in the _1/6. The reason why the remembering width W ₀ and W _1, taking into account such that there is a range of frequencies of the noise, W _0, if the W ₁ in the range of the degree silencing effect utilizing resonance Is obtained. This point has also been confirmed by experiments performed by the inventors.

Next, the interval H ₀ between the sound-absorbing splitters 4 and 5,
H ₁ is at equal pitch intervals of substantially the same length as W ₀ and W ₁ , respectively, so as to have a structurally appropriate size. The number of the sound-absorbing splitters 4 and 5 is determined in consideration of the noise level, the target noise amount after silencing, the allowable air resistance, and the like. The reason why the sound absorbing splitters 4 and 5 are slightly inclined is to reduce the passage resistance of the exhaust gas within a range that does not significantly reduce the noise reduction effect, and these are arranged at right angles to the flow of the exhaust gas. The good thing is, of course.

In the above embodiment, only the noise of the fundamental frequency and the second harmonic of the noise spectrum is targeted.
In order to further improve the noise reduction performance of the muffler, a noise attenuator for the third and fourth harmonics is added, or a muffler having such a noise attenuator is shown in FIG. It can be additionally provided downstream of the silencer.
Further, in this embodiment, an exhaust gas system of a coal-fired boiler is taken as an example, but the present invention is not limited to this, and an exhaust gas system such as a garbage incinerator, a pneumatic transportation device, a tunnel / tunnel construction site, etc. Needless to say, the present invention can be applied to an exhaust system.

[0016]

As described above, according to the present invention, according to the first aspect of the present invention, since the sound attenuating member simultaneously attenuates noise due to resonance and absorbs noise due to the sound absorbing material, a large noise suppressing effect is obtained. be able to. In addition, by increasing the opening ratio of a large number of small holes covering the sound absorbing material, it is possible to prevent the pores from being blocked by solids in the gas, and to prevent the sound absorbing material from scattering even in such a case. Can be.

According to the second aspect of the present invention, when there are a plurality of specific frequencies, the silencer is constituted by a plurality of silencers corresponding to the respective frequencies. Noise can be effectively silenced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a muffler according to an embodiment.

FIG. 2 is an explanatory diagram showing an example of a conventional silencer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Duct 2 Noise attenuation part A ₀ zone (sound absorption part) 3 Noise attenuation part A ₁ zone (sound absorption part) 4 Sound absorption splitter (sound absorbing member) 5 Sound absorption splitter (sound absorbing member) 6 Casing (closing member) 7 Casing (closing member) 9 sound absorbing material 10 small hole

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F16L 55/02-55/035 F23J 11/00 F01N 1/00-1/24 G10K 11/16

Claims (2)

(57) [Claims] 1. A silencer installed in a duct through which a gas flows to effectively reduce noise that increases at a specific frequency, wherein the silencer is perpendicular to or inclined to the flow direction of the gas and is spaced apart in the flow direction. A sound-absorbing section including a plurality of arranged sound-absorbing members and a closing member for closing one end of the plurality of sound-absorbing members, wherein the sound absorbing member has a sound-absorbing material and a gas flow filled therein. A number of small holes provided on the downstream side in the direction, the depth of the space portion formed by the silencing member and the closing member in the direction perpendicular to the flow direction, the wavelength of the noise that increases at the specific frequency Muffler characterized in that it is 1/3 to 1/6. 2. The method according to claim 1, wherein the specific frequency includes a plurality of specific frequencies, and the muffling unit is configured to increase a depth of the space portion in a direction perpendicular to the flow direction by 1/1 of each wavelength of the noise that increases at the plurality of frequencies.
The muffler according to claim 1, comprising a plurality of mufflers each having a size of 3 to 1/6.