CA2082988C

CA2082988C - Excessive noise preventer

Info

Publication number: CA2082988C
Application number: CA002082988A
Authority: CA
Inventors: Wiktor M. Jungowski; Grazyna Petela
Original assignee: NOVA Gas Transmission Ltd
Current assignee: NOVA Gas Transmission Ltd
Priority date: 1992-11-16
Filing date: 1992-11-16
Publication date: 2002-11-26
Anticipated expiration: 2012-11-16
Also published as: CA2082988A1

Abstract

A device for the prevention of noise generation during the expansion of high pressure fluid (i.e. gas or steam) stream. The preventer comprises a housing which consists of an inner wall and a larger outer wall. The inner and outer walls both have the shape of a hemisphere and are perforated to allow fluid to flow through them. An enclosed space between both hemispheres contains a granular packing which creates a tortuous path for the flowing fluid. The preventer may find application in such installations as compressor stations (as a blowdown noise suppressor), gas metering stations and power plants.

Description

~U8~988 FIELD OF TEIE INVENTION
This invention relates to a throttling device which prevents the generation of high level noise associated with the release of a high pressure gas or steam, referred to later as a "fluid", into the atmosphere.
BACKGR~UND OF T1EIE INVENTION
Many industrial processes require the release of a high pressure fluid into the atmosphere. This type of release occurs through, for example, safety or relief valves installed in compressor stations, gas metering stations, cryogenic facilities and power plants. These releases generate a noise which is sufficiently severe to be referred to as a type of pollution. Noise pollution is now frequently subject to regulations, laws and control orders, particularly in urban areas.
Thus, a need clearly exists for a device to prevent excessive noise generation (i.e. the device actually reduces the amount of noise that is generated, but does not necessarily prevent all generation of noise). Such a device should not be too large or expensive. To be effective, the device should fulfil the following three general principles:
1. The device should provide effective throttling, which can be achieved by splitting the gas flow into numerous small streams characterized by low 3 0 velocities. This results in high pressure drop and low turbulence with the absence of flow oscillation.

2. The device should avoid discontinuity regions in the gas flow, which are responsible for flow oscillations and increase of noise production.

3. The device should reduce the characteristic dimensions responsible for noise generation. This changes the character of the generated noise into a noise of higher frequency which is less harmful arid easier to attenuate.
All these requirements have been satisfied when the fluid flow was forced either through a porous material or through metal disks having expanding passage grooves. The porous material used in the first approach is known to those skilled in l0 the art as "sinter" and has been utilized to prevent intermittent noise from various pneumatic devices. However, in the case of long duration venting with a high flow rate, this approach would require an enormously sized noise preventer which would become blocked very quickly by any dust particles in the flowing medium. The second approach is utilized in the commercially available "atmospheric resistors", sold by Control Components Inc. of California, U.S.A. However, in this case the 2 0 fabrication of the disks is very expensive and the disk stacks are large and very heavy.
Typical noise mufflers that are used, for example, for blowdown noise suppression, do not prevent noise generation, but can suppress noise only.
Additionally, they also have extremely large dimensions and are very expensive.
SUMMARY OF THE INVENTION
The present invention provides:
3 o A noise preventer consisting of:
(i) a housing adapted to receive said discharge, and (ii) packing contained within said housing, wherein said housing is characterized by:

~~~298g (a) a first wall having a shape described by a partial first sphere, and containing a plurality of perforations;
(b) a second wall having a shape described by a partial second sphere, and containing a plurality of perforations, wherein the diameter of said second sphere is larger than the diameter of said first sphere, and wherein said second sphere is concentric with said first sphere so as to define a partial spherical space between said first wall and said second wall, and (c) additional housing surface with extends from said first wall to said second wall, such that housing surface, said first wall and said second wall substantially enclose said partial spherical space.
2Q In another embodiment, the present invention provides:
A process to suppress the noise associated with the expansion of a high pressure fluid, wherein said process consists of affixing a noise preventer according to this invention to a discharge line connected to said fluid such that said noise preventer xeceives a discharge flow of said fluid, and subsequently causing a discharge flow of said fluid through said discharge line.
3 0 DETAILEIa DE~CRIPTIOhI
The invention will now be described in detail with reference to the accompanying Figure 1 which is a side view of a section of a noise preventer according to the invention.

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Referring to Figure l, the noise preventer 1 must contain a housing 2 which is adapted to receive a high pressure fluid discharge. The housing 2 consists of a first wall 2a, a second wall 2b, and an additional housing surface 2c.
First wall 2a and second wall 2b each describe a partial circular arc in cross section (as shown in Figure 1), as both of first wall 2a and second wall 2b have a shape which describes a partial sphere.
The hemispherical shape indicated in Figure 1 is highly preferred, although small deviations therefrom may be permitted (particularly if such deviations facilitate the fabrication and/or use of the noise preventer). For example, a small cylindrical lip (not shown) may be integrally formed with, or attached to, the bottom of partial spheres 2a and 2b in order to facilitate attachment of the partial spheres to the frame 7.
2 0 Additional housing surface 2c substantially encloses a space 3 between the two partial spheres formed by the first wall 2a and the second wall 2b. In the embodiment illustrated in Figure l, the additional housing surface simply constitutes a part of the frame ? (i.e. the partial spheres of first wall 2a and second wall 2b are Laid on top of the frame 7, as shown in Figure 1, such that the frame ? closes in the bottom space therebetween. However, as shown in Figure l, frame 7 contains a circular hole 30 which cooperates with inner wall 2a to allow fluid flow into the housing 2).
Thus, one function of frame ? is to enclose the bottom space between the partial spheres 2a and 2b (as shown in Figure I).
For convenience, the space 3 between the two partial spheres is referred to herein as the "partial spherical space" 3.

2a8~98g The partial spherical space 3 contains a packing which produces a tortuous path between the inner wall 2a and outer wall 2b. The packing most preferably consists of a plurality of particular pieces or granules. It is not intended to narrowly restrict the present invention to the use of granules of a specific size, shape and material of construction. However, the size of the granules is preferably selected on the basis that small particles will typically provide improved noise control (i.e.
smaller is typically better with respect to noise control), but with the expectation that contaminants, such as dust, in the fluid being vented through the noise preventer may foul small particles more quickly than large particles (i.e. larger particles are less prone to fouling). As a practical guideline, the use of particulate pieces which have a volume of from about 40 mm' to 750 mm' are especially preferred (to put this in perspective, the first volumes correspond to the volume of a sphere having a diameter of slightly more than 4 mm and the second volume corresponds to the volume of a sphere having a diameter of slightly more than 11 mm).
First wall 2a and second wall 2b both contain a plurality of perforations to allow fluid flow through the housing. It will be appreciated that the size of these perforations must be small enough to prevent the above described particular pieces from leaking out through the perforations. Circular perforations are preferred.
o For ease of fabrication, it is especially preferred to fabricate the first wall 2a and second wall 2b from pre-perforated steel plate. Such pre-perforated steel plate is a well known article of commerce.
The additional housing provided by frame 7 is not perforated.

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Figure 1 also shows a shroud 4. The shroud 4 is optional and does not constitute an essential element of this invention. The shroud 4 encircles the noise preventer, but it is open at the top end 4t.
The primary function of the shroud is to direct fluid which exits through the perforations in outer wall Zb in an upwards direction. This is especially desirable if the fluid is flammable (for example, it is desirable to direct the natural gas which is released during the blowdown of a natural gas compressor station in an upwards direction, so as to reduce the probability of ignition).
Figure 1 also illustrates a diffuser section S. The diffuser section 5 does not directly constitute a part of the noise preventer of this invention. ~Iowever, in some cases, it may be necessary to employ a diffuser for the purpose of reducing the velocity of the fluid which enters the noise preventer.
z 0 The operation of a noise preventer of this invention is described below.
Fluid enters the preventer in the direction indicated by labelled arrow F.
The diameter of pipe 6 is less than the diameter of the hemisphere of inner wall 2a, so the conical diffuser 5 connects the pipe to the inner wall 2a.
The fluid passes through the perforations of the first wall 2a and encounters the particulate pieces (not shown) contained within partial spherical space 3. The fluid 30 then passes through the perforations of the second wall 2b and exits the noise preventer.
Further details are given in the following, non-limiting example.

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)Jxam 1e A noise preventer according to this invention was constructed, then installed on the discharge line or "vent pipe" of a natural gas, compressor (and used to suppress the noise generated during a blowdown through the vent pipe).
The noise preventer was similar to the one shown in Figure 1, with the 1 o dimensions given below:
(a) the inner wall (2a in Figure 1) was hemispherical and had a diameter (2a~ in Figure 1) of about 207 mm;
(b) the outer wall (2b in Figure 1) was also hemispherical and had a diameter (2b,, in Figure 1) of about 592 mm.
The housing (inner wall 2a and outer wall 2b) was constructed from steel having a thickness of about 6.3 mm.
2 o The inner and outer walls 2a and 2b both contained a plurality of circular perforations, which were spaced on about 9 mm centres. The diameter of the circular perforations was about 6 mm. The spherical space 3 was packed with particulate pieces having a nominally spherical shape (average diameter 8 mm). The particulate pieces were made from dragonite glass.
As indicated in Figure l, the outer wall 2b and inner wall 2a are attached to 30 the frame or "base flange" 7 (such that base flange 7 functions as additional housing which encloses the bottom space between the inner wall 2a and outer wall 2b).
The noise preventer was bolted to the frame through a plurality of radially spaced bolt holes 8.
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The shroud (part 4 in Figure I) was bolted to the base flange 7 through a plurality of bolt holes 9.
A conical diffuser 5 was integrally attached (welded) to the base flange 7, such that fluid flow through the diffuser was received by the first wall 2a.
In turn, the conical diffuser 5 was bolted through bolt holes 10 to a pipe 6 2o carrying the discharge from the blowdown of a natural gas compressor.
(The term "blowdown" is used in this example to describe the venting of natural gas from compressor station piping.) Natural gas at a mass flow rate of 40.3 kilograms per second (and at a pressure of 5544.1 kilo Pascals and a temperature of 4°C) was vented through the above described noise preventer.
The noise level generated by the blowdown was significantly reduced by the 2 o noise preventer. Specifically, the noise level was more than 20 dB less, in comparison to the venting in the absence of the preventer.
The noise preventer of the Example has demonstrated its effectiveness for the natural gas flow rate described above.
It will be appreciated that different sizes of noise preventers may be appropriate for significantly different flow rates. In this context, the following scale-3 o up criteria are preferred:
(a) for increased mass flow rate, it is preferred to leave the distance between the hemispheres the same but to increase the cross-sectional area described by inner wall 2a and outer wall Zb (i.e. by increasing the diameter of both hemispheres 2a and 2b, respectively);

2~18298g (b) for increased pressure, it is preferred to increase the partial spherical space 3 by increasing only the diameter of outer wall 2b and to add more particulate pieces (i.e. to enlarge outer wall 2b, and add more particulate pieces).

Claims

1. A noise preventer consisting of:
(i) a housing adapted to receive a fluid discharge, and (ii) backing contained within said housing, wherein said housing is characterized by:
(a) a first wall having a shape described by a partial first sphere. and containing a plurality of perforations;
(b) a second wall having a shape described by a partial second sphere, and containing a plurality of perforations, wherein the diameter of said second wall is larger than the diameter of said first wall, and where said second sphere is concentric with said first sphere so as to define a partial spherical space between said first wall and said second wall. and (c) additional housing surface with extends from said first wall to said second wall, such that housing surface, said first wall and said second wall substantially enclose said partial spherical space.

2. The noise preventer of claim 1 wherein said packing consists of a plurality of particulate pieces.

3. The noise preventer of claim 2 wherein said particulate pieces are essentially spherical.

4. The noise preventer of claim 3 wherein the diameter of said particulate pieces is between 4 and 11 mm.

5. The noise preventer of claim 1 wherein said first wall and said second wall both have a shape described by a hemisphere.

6. The noise preventer of claim 5 wherein said housing is constructed from metal.

7. The noise preventer of claim 5 wherein said housing is constructed from plastic.

8. A process to suppress the noise associated with the expansion of a high pressure fluid, wherein said process consists of affixing the noise preventer of claim 1 to a discharge outlet end of a discharge line for the purpose of reducing the noise associated with the venting of pressurized gas to atmosphere. That said noise preventer receives a discharge flow of said fluid, and subsequently causing a discharge flow of said fluid through said discharge line.