JET NOISE SILENCER

SILENCIEUX ATTENUANT LE BRUIT PRODUIT PAR UN JET

English Abstract

A device is invented to attenuate excessive noise generated by a free jet during high
pressure fluid (a gas or a vapor) release. The silencer consists of a chamber surrounded by
perforated walls, and filled with a granular packing which creates large contact surface with the
fluid flowing through the chamber. The high pressure energy of fluid is effectively dissipated by
the friction between the fluid and the surface of solid packing. The fluid, before it enters the
chamber, is swirled by motionless vanes in the silencer swirler. The swirling distributes uniformly
the fluid through the granular packing in the chamber. The fluid flow rate can be controlled by the
valve installed upstream of the swirler. The flow rate during first period of blowdown can be kept
constant in spite of the pressure drop of evacuated fluid. This option of the controlled fluid rate
would allow for small size of the silencer without increasing time required for full discharge of the
fluid, so the silencer is amenable to portable application.
The jet noise silencer can find application in the installations operating with high
pressure, e.g., power plants, chemical plants, pipelines systems, cryogenic facilities, compressor
stations, etc.

French Abstract

Dispositif visant à atténuer les bruits excessifs produits par un jet libre lors du dégagement d'un fluide (gaz ou vapeur) haute pression. Le silencieux se compose d'une chambre entourée de parois perforées et remplie d'un garnissage granulaire qui crée une importante surface de contact avec le fluide s'y écoulant. L'énergie du fluide haute pression est dispersée efficacement à cause de la friction entre le fluide et la surface du garnissage plein. Le fluide, avant d'entrer dans la chambre, est agité par des aubes fixes dans le diffuseur du silencieux. Le tourbillonnement permet de répartir uniformément le fluide dans le garnissage granulaire de la chambre. Le débit peut être commandé par le robinet installé en amont du déflecteur. Pendant la première période de purge, le débit peut être maintenu constant malgré la baisse de pression du fluide évacué. La possibilité d'obtenir un débit contrôlé pourrait permettre l'utilisation de silencieux de petite taille sans devoir augmenter la durée de vidange complète du fluide, de sorte que le silencieux est portatif. Le silencieux de bruit de jet peut servir dans des installations fonctionnant à haute pression, p. ex., les centrales, usines chimiques, systèmes de pipelines, installations cryogéniques, stations de compression, etc.

Claims

Claims
1. The silencer consists of a valve with the controlled and programmed opening, a stationary
swirler to swirl a fluid jet, a silencer chamber through which the fluid jet is discharged and the
exit shroud.
49

2. The silencer, in which a fluid flow rate through the silencer chamber can be programmed and
appropriately adjusted during the entire period of fluid discharge.
3. The silencer, which is portable.
4. The silencer chamber is characterized by:
(a) The chamber inlet and outlet walls, which are both made of the perforated
material containing plurality of perforations with the same opening size
between 3 and 10 mm
(b) The chamber inlet and outlet walls which are concentric.
c) The chamber inlet and outlet walls which are of identical geometry and they both
assume any of the geometrical shapes listed below, (i-viii), or the chamber inlet and
outlet walls which are of different shapes, representing any combination of the listed
below shapes, (i-viii):
(i) partial sphere
(ii) cylinder
(iii) cone or frustum of cone
(iv) pyramid or frustum of pyramid
(v) polyhedron
(vi) paraboloid
(vii) cube
(viii) rectangular
d) A volume between the inlet and outlet walls of the silencer chamber, which is tightly
packed with granular material characterized by:
(i) the uniform or different sizes of granules
(ii) the size of uniform granules or the minimum size of non-uniform granules is
larger than the perforation openings
5. A swirler of the silencer is located upstream of the silencer chamber, at the chamber inlet.
The swirler comprises the stationary vanes to swirl the fluid and ensure uniform fluid distribution
in the silencer chamber inlet.

6. A valve of the silencer is used in the mode of controlled flow operation. The valve is equipped
with an automatic control system which is characterized by:
a) The program which controls the valve opening appropriately to adjust the flow rate of
fluid entering the swirler in such a way that during the entire period of fluid discharge
the generated noise does not exceed the required level.
b) The control system is programmed to reduce the flow rate at the beginning of the
discharge to prevent generation of the maximum attainable noise level, and to increase
low rate in the last phase of the discharge, when generated noise is below the required
level. This mode of flow rate control results in maintaining almost constant noise level
during the entire fluid discharge.
7. The shroud of the silencer can be a cylindrical or a reversed frustum of cone shape.

Description

2 1 9772 ~
JET NOISE SILENCER
Abstract of the Invention
A device is invented to attenuate excessive noise generated by a free jet during high
pressure fluid (a gas or a vapor) release. The silencer consists of a chamber surrounded by
10 pelrurdled walls, and filled with a granular packing which creates large contact surface with the
fluid flowing through the chamber. The high pressure energy of fluid is effectively dissipated by
the friction between the fluid and the surface of solid packing. The fluid, before it enters the
chamber, is swirled by motionless vanes in the silencer swirler. The swirling distributes uniformly
the fluid through the granular packing in the chamber. The fluid flow rate can be controlled by the
15 valve installed upstream of the swirler. The flow rate during first period of blowdown can be kept
constant in spite of the pressure drop of evacuated fluid. This option of the controlled fluid rate
would allow for small size of the silencer without increasing time required for full discharge of the
fluid, so the silencer is amenable to portable application.
The jet noise silencer can find application in the installations operating with high
20 pressure, e.g., power plants, chemical plants, pipelines systems, cryogenic facilities, compressor
stations, etc.
Field of the Invention
The invention relates to attenuation of high level noise generated by a jet of a high
25 pressure gas or vapor, referred to later as a "fluid", released into the atmosphere.
Background of the Invention
Many industrial processes require release of large volume of fluid at high pressure into
the atmosphere. The fluid is released from safety or relief valves installed e.g., in power plants,
30 chemical plants, cryogenic facilities, compressor stations, gas metering stations, etc. Fluid

2 1 q772 1
pressures can reach e.g. 15 MPa and the noise generated by the jet can approach an A-weighted
sound level of 150 dB. The severe noise of the jet is recognized as a form of pollution which is
the subject to regulations, especially in populated areas. Devices are needed to obtain the jet
noise at acceptable levels. However, most of commercially available silencers are very large and
5 expensive.
The invented silencer is simple to manufacture, effective and has small dimensions. Its
operation is based on the concept of attenuating the noise of fluid jet at the source, which is
mostly the high jet velocity resulting from conversion of the fluid high pressure energy. This
conversion process progresses in the silencer as fluid flows through the silencer chamber filled
10 with the granular packing material. Due to large friction between fluid and surface of packing
material, fluid flow is throttled and the pressure energy is fluently ~1issiratin9~ preventing from
development of high fluid velocities. A spacious volume of uniform packing in the silencer
chamber has no macro geometrical discontinuities, what eliminates occurrence of vibrations or
oscillations which might contribute to noise generation. Small size of the solid packing material is
15 pertinent to noise generation at high frequencies, which is less harmful and easier to attenuate.
Summary of the Invention
The invented silencer attenuates the excessive noise generated by a free jet during high
release of pressure fluid. The silencer can be used for a range of pressures, exceeding 5 MPa,
20 and for fluid rate releases, which may exceed 100 kg/s.
Attenuation of jet noise occurs as the fluid flows through the silencer chamber made of
the inlet and outlet perforated walls and filled with tightly packed granular material. The
geometric configuration of the chamber is such that the total cross section area of perforation
openings at the chamber outlet is appropriately larger than the total cross section area of
25 perforation openings at the chamber inlet. This condition can be fulfilled for different shapes of
the chamber inlet and outlet walls. These walls should be concentric, and they can have either
identical geometrical shapes such as the frustum of cones, cone, cube, pyramid, or they can be
any combination of the said shapes, e. 9. inlet wall is a cone and outlet wall is a frustum of cone

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with different inclination angle. The ultimate design of the chamber shape depends on the
properties of the released jet, effectiveness and fabrication cost.
A granular filling of the silencer chamber creates a large surface of contact with the fluid
flowing through the chamber. As the fluid propagates through the chamber, its high pressure
S energy is effectively dissipated due to the friction between the fluid and the large solid surface of
packing. In order to avoid excessive motion of filling particles caused by fluid flow, which can
damage the particles, compact packing is required.
Before the fluid enters the chamber, it is swirled by motionless vanes of the silencer
swirler located in the stack upstream of the chamber, close to the chamber inlet. Swirling helps
10 to distribute the fluid entering the inner wall of silencer in uniform way and, consequently,
through the packing space in the chamber.
The silencer can operate in two optional modes: with the non-controlled fluid flow rate
during relatively small releases or with the controlled flow rate through the silencer. The fluid flow
rate can be controlled with the valve installed downstream of the swirler. The opening of the
15 valve can be controlled (programmed) to maintain the following flow rate schedule: during the
controlled flow rate release, fluid flow rate is reduced and kept constant in the first period of the
release, in spite of the pressure drop of evacuated fluid. This maintained constant flow rate,
which is below the maximum flow rate attainable with the initial high pressure level in the
evacuated fluid, prevents the excessive jet noise generation during the first phase of the
20 discharge. As the pressure in the evacuated fluid decreases, valve opening can be gradually
increased to compensate for the initial reduced flow rate. As a result, the total evacuation time is
not extended, and the maximum noise level generated in the very first period of evacuation is
avoided. This strategy of the controlled flow rate allows for small size of the silencer. As the size
and weight of the silencer is small, it can be easily transported, e.g., as a mobile silencer unit.
2~ The fluid leaving the silencer flows into the shroud of cylindrical or divergent cone shape.
The shroud is used to further reduce the noise and direct vertically the expanded jet into
atmosphere.
The silencer has simple construction and is easy to fabricate.

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D~eailed Description
Further details of the invented silencer are given in the following, non-limiting example.
The invention is described with reference to the acco",pan~;ng Figure 1, which is a half side
5 view and a half side view of a section of a silencer, according to the invention.
Referring to Figure 1, the silencer must contain a chamber which is formed by the
perforated frustum of outer (outlet) cone 1 and perforated frustum of inner (inlet) cone 2, and the
non-perforated annular plate 3. Packing contained within the chamber consists of plurality of
separate pieces, tightly packed, made of the erosion, stress and thermal resistive solid material.
I0 The frustum of cones 1 and 2 are fastened to plate 3 with flanges 4 and 5. The conical shroud 6
is fastened to plate 3 with flange 7. The plate 3 is also used as a flange to connect the chamber
~, with diffuser 8, which reduces the flow velocity of the fluid. The diffuser 8 contains swirling vanes
9. The swirling results in uniform distribution of fluid within the hemispherical solid angle at the
diffuser outlet. A cylindrical connector 10, with flange 11, connects diffuser 8 with the blowdown
15 valve 12. The valve controls the flow rate of fluid through the chamber. Noise sensor could be
used to control the valve opening; the valve opens more as noise level decreases. As an
alternative to the noise sensor, other sensors could be used, e.g., a pressure sensor; which
increases valve opening in the second phase of evacuation, when pressure in evacuated fluid
decreases. The silencer described above is mounted on the vertical stack used, for discharge of
20 fluid.

Representative Drawing